Dr Stephen Brett

• Consultant in Intensive Care Medicine
• Imperial College London
• Hammersmith Hospital
• Du Cane Road, London

However anxiety bc venlafaxine 37.5 mg buy without prescription, occult mitral stenosis from rheumatic heart disease is still encountered on occasion and can lead to severe left heart failure in the presence of tachycardia and/or volume loading anxiety symptoms paranoia buy discount venlafaxine 37.5 mg line. The Revised Cardiac Risk Index will be discussed throughout the rest of the chapter anxiety symptoms definition cheap 75 mg venlafaxine visa. Approach to the Patient the preoperative evaluation/consultation begins with a thorough history and physical examination anxiety 7 minute test cheap 150 mg venlafaxine free shipping. Frequently anxiety symptoms zinc purchase discount venlafaxine on-line, patients are evaluated because of the presence of overt coronary artery disease. The perioperative period is associated with a hypercoagulable state, and therefore the presence of unstable coronary artery disease is associated with a very high rate of perioperative cardiac morbidity and mortality. For most surgical procedures, oral anticoagulation should be stopped three days before surgery with the goal of an international normalized ratio <1. Patients may receive heparin perioperatively with discontinuation 4 to 6 hours prior to surgery. If necessary, antihypertensives can be administered intravenously in the perioperative period to acutely lower blood pressure. Patients with signs of unstable hypertension such as angina or headache should have surgery delayed and the blood pressure treated first. Patients with congenital heart disease should be evaluated for Eisenmenger syndrome and pulmonary hypertension. A full review of this topic is beyond the scope of this chapter; it can be found elsewhere. Asymptomatic ventricular arrhythmias have not been associated with an increase in cardiac complications. Patients with ventricular arrhythmias should only be treated if the arrhythmia causes hemodynamic compromise. Cardioversion should be performed for those with unstable arrhythmias; otherwise, rate control with medication is sufficient. The figure presents in algorithmic form a framework for determining which patients are candidates for cardiac testing. In many instances, patient- or surgery-specific factors dictate an obvious strategy. Cardiac evaluation and care algorithm for noncardiac surgery based on active clinical conditions, known cardiovascular disease, or cardiac risk factors for patients 50 years of age or older. Depending on the results of the test or interventions and the risk of delaying surgery, it may be appropriate to proceed to the planned surgery with maximal medical therapy. In these patients, interventions based on cardiovascular testing in stable patients would rarely result in a change in management, and it would be appropriate to proceed with the planned surgical procedure. In highly functional asymptomatic patients, management will rarely be changed on the basis of results of any further cardiovascular testing and it is therefore appropriate to proceed with the planned surgery. If the patient has poor functional capacity, is symptomatic, or has unknown functional capacity, then the presence of clinical risk factors will determine the need for further evaluation. If the patient has no clinical risk factors, then it is appropriate to proceed with the planned surgery, and no further change in management is indicated. In patients with three or more clinical risk factors or if the patient is undergoing vascular surgery, recent studies suggest that testing should only be considered if its outcome could change management. In nonvascular surgery in which the perioperative morbidity related to the procedures ranges from 1 to 5% (intermediate risk surgery), there are insufficient data to determine the best strategy (proceeding with the planned surgery with tight heart rate control with beta-blockade or further cardiovascular testing if it could change management). It has a low positive predictive value, so it is best used in those with high clinical risk for cardiac events. For those with a left bundle branch block, a pharmacological stress test is preferred over an exercise stress test. The optimal test is best left to the discretion of the cardiologist based upon local expertise, although several meta-analyses have suggested that dobutamine stress echocardiography has the best sensitivity and specificity for predicting perioperative cardiovascular complications. A magnet may be useful during surgery to disable the unit; however, not all units behave in the same manner with magnet placement, and an electrophysiologist or the manufacturer of the device should be contacted for information. If a unipolar unit must be used, then short, intermittent, and irregular bursts should be employed as far as is possible from the unit and leads. If a patient is pacer-dependent, then the device and battery status should be evaluated within 3 to 6 months before the surgical procedure. There are no Class I recommendations for performing a static assessment of ventricular function. It is reasonable to order this for patients with dyspnea of unknown origin or current or prior heart failure with worsening symptoms or other change in clinical status if an assessment has not been performed within 12 months. Exercise stress testing is rarely a diagnostic benefit for patients with good exercise tolerance. Stress nuclear perfusion imaging has a high sensitivity for detecting patients at risk for perioperative cardiac events, with the risk being proportional Medications There is increasing evidence that patients should continue to take their cardiovascular medications in the perioperative period. Specifically, beta-blockers and statins should be continued throughout the perioperative period. Multiple studies have demonstrated improved outcome in patients that are given perioperative beta-blockers, especially if heart rate is controlled. However, newer studies have demonstrated that beta-blockers may not be beneficial if heart rate is not well-controlled or in lower risk patients. In the 2009 update, beta blocked titrated to heart rate and blood pressure are probably recommand in those with a positive stress test undergoing major vascular surgery, although acute administration without titration may be associated with harm. The cholesterol lower statins also have antiinflammatory and plaque-stabilizing properties. Durazzo and colleagues published a randomized trial of 200 vascular surgery patients in which statins were started an average of 30 days prior to vascular surgery. A significant reduction in cardiovascular complications was demonstrated using this protocol. Le Manach and colleagues demonstrated that statin withdrawal greater than 4 days was associated with a 2. It is reasonable to prescribe statins for those undergoing vascular surgery or those with at least one clinical risk factor and undergoing intermediate risk. Poldermans and colleagues demonstrated reduced perioperative cardiac morbidity with administration of 30 days of preoperative fluvastatin compared to placebo in intermediate risk patients. Central alpha-2-agonists, such as clonidine, may be useful in those who cannot tolerate beta-blockers. These drugs are associated with better hemodynamic stability, suppress sympathetic stimulation, and also have a sedating effect. There is a reduced mortality in intermediate and vascular surgery and for those with at least one clinical risk factor with clonidine use. They do not decrease myocardial ischemia; however, verapamil is associated with a decreased incidence of supraventricular tachycardia. There is anecdotal evidence that aspirin discontinuation is associated with an increased incidence of perioperative cardiac complications. This has been shown in patients with drug-eluting stents, but may also be true in other patients with high risk coronary lesions. The perioperative of aspirin withdrawal between 7 and 14 days may be associated with hypercoagulability. Within 30 days after the vascular operation a postoperative myocardial infarction, defined by elevated troponin levels, occurred in 12%of the revascularization group and 14%of the no-revascularization group (p = 0. The authors suggested that coronary revascularization is not indicated in patients with stable coronary artery disease. Additionally, patients with left main disease have a long-term survival benefit from coronary revascularization. Poldermans and colleagues randomized 770 patients having major vascular surgery and considered as having intermediate cardiac risk, defined as the presence of one or two cardiac risk factors, to either undergo further risk stratification with stress imaging or proceed right to surgery. The conclusion of the authors was that further risk stratification in this group of patients considered at intermediate risk based on clinical history alone was unnecessary as long as perioperative beta-blockers were used, and testing only delayed necessary vascular surgery. Coronary stent placement may be a unique issue, and several studies suggest that a minimum of 30 days is required before the rate of perioperative complications is low. Several reports suggest that drug-eluting stents may represent an additional risk over a prolonged period (up to 12 months), particularly if antiplatelet agents are discontinued. The new guidelines suggest continuing aspirin therapy in all patients with a coronary stent and discontinuing clopidogrel for as short a time interval as possible for patients with bare-metal stents <30 days or drug-eluting stents <1 year. Blood Pressure and Heart Rate Management Hypertensive patients tend to have exaggerated intraoperative blood pressure fluctuations and lability. Low blood pressure should be avoided because of the shift of the autoregulation curve of cerebral perfusion in hypertensive patients. Table 14-3 lists the optimal management of blood pressure, heart rate, and contractility for those with several difference kinds of heart lesions. One should take in to account the level of training of those using the equipment and interpreting the information, and type of equipment available. Because of the potential complications, using less invasive monitoring is best when possible. General anesthesia is drug-induced amnesia, analgesia, unconsciousness, paralysis, and autonomic system control. The patient is unarousable, even to painful stimuli, and often needs ventilation either with a mask, laryngeal mask airway, or endotracheal tube. Intravenous and/ or inhalational agents are used as a balanced anesthetic technique. Inhalational agents in addition to nitrous oxide are used most commonly and include desflurane, isoflurane, and sevoflurane. They depress cardiac output in a concentration-dependent manner by decreasing systemic vascular resistance, preload, afterload, and contractility. There is no increase in myocardial ischemia or infarction with inhalational versus noninhalational techniques. Inhalational agents may possess a protective effect on the myocardium similar to ischemic preconditioning. Propofol, which is a common induction agent and maintenance infusion drug, can decrease heart rate, preload, afterload, and contractility. Opiods can decrease heart rate, preload, and afterload; this is especially the case with opiods that cause histamine release such as morphine. There are minimal hemodynamic effects with nerve blocks and they may be supplemented with sedation or general anesthesia. Treatment includes pressor support with ephedrine or phenylephrine and intravascular fluid support. High levels above a T4 dermatomal level have the greatest effect on sympathetic stimulation of the heart. Contraindications to epidural and spinal anesthesia include patient refusal, coagulopathy, allergy to the agents used, systemic or local infection, and neurological abnormalities. If there is inadequate nerve blockade, the anesthesiologist may have to convert to a general anesthetic. Epidural catheters are also useful for postoperative pain relief in some abdominal, orthopedic, and thoracic surgeries. There is also a high incidence of respiratory complications because of sedation without airway protection. Other Considerations During Surgery Normothernia can reduce perioperative morbidity. Aggressive glucose control may reduce postoperative wound infections and other morbidities, although this remains controversial. In the absence of randomized trials, current nonrandomized evidence suggests that hemoglobin should be maintained at greater than 9 mg/dL in those with active cardiovascular disease. Fluid overload should be avoided especially in those with a low ejection fraction. The decrease in preload associated with nitroglycerin may lead to hypotension, and therefore use of this agent is not recommended prophylactically. The levels are not necessarily useful in those with clinically stable disease who have had vascular or intermediate risk surgery. They may be caused by plaque disruption and coronary thrombosis in a critical fixed stenotic area or noncritical stenotic area, as seen with tachycardia and the hypercoagulable postoperative state. The nidus may be associated with an area of noncritical stenosis and may not be detected before surgery. Noncritical stenotic areas do not have collateral coronary flow and a prolonged increase in myocardial oxygen demand may result in ischemia or infarction. Postoperative arrhythmias may be due to infection, hypotension, metabolic derangements or hypoxia. Premature ventricular contractions are not worrisome if the patient is hemodynamically stable. Pain control is important in avoiding the tachycardia and sympathetic surge after surgery. Pain management should be tailored to the patient and procedure when one is choosing between a patient-controlled analgesia pump versus an epidural catheter. Blood pressure-lowering agents, especially beta-blockers and clonidine, should be continued postoperatively. Anticoagulation may be more beneficial for medical management with heart rate and blood pressure control. Left ventricular evaluation, angiography, and the assessment of long term risk should take place during the same hospital stay. Prevention of venous thromboembolism: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th ed. Therefore, right heart catheterization is required to confirm a diagnosis of pulmonary arterial hypertension. One of the most important determinants of survival is functional capacity and the most common cause of death is right ventricular failure. Females are more commonly affected and the disease has a tendency to develop at earlier ages in subsequent generations (genetic anticipation).

Circumferential full-thickness skin punch biopsies (6 mm) should be sent for frozen section analysis following skin prep and induction anxiety disorder key symptoms venlafaxine 37.5 mg purchase with amex. Preferentially a minimal 2-cm margin developed 360 degrees about the periphery of the planned resection area is ideal anxiety symptoms in children 37.5 mg venlafaxine buy amex. Use of a punch biopsy (4 to 6 mm) should be taken approximately every 1 to 2 cm about the tumor margin resection to validate a negative pathological margin before opening the chest anxiety symptoms checklist pdf venlafaxine 37.5 mg order with visa. Bronchial washings may be appropriate to rule out direct lung invasion if suspicious by imaging anxiety 40 year old woman 37.5 mg venlafaxine buy with amex. A latissimus pedicle flap is the most versatile and is usually the most readily available anxiety 33625 venlafaxine 75 mg buy overnight delivery. Once negative margins are confirmed with pathology, the extent of the incision through the skin overlying the pectoralis major muscle may be completed using cold blade and, thereafter, electrocautery for subcutaneous and muscular tissues. Technique of Resection the pectoralis major and minor are incised outside the tumor-bearing area to the level of the chest wall; all ribs for planned resection are medially and laterally exposed. In the cephalad-most extent of the planned rib resection, the rib is incised on its cephalad surface, and the ipsilateral lung is deflated by the anesthesiologist at the instruction of the surgeon. The thoracotomy should be initiated via the superior margin of the planned resection. Upon entering the thorax, previous pleural adhesions created by prior radiation therapy and/or surgery should be sharply dissected and mobilized. Attention must be directed to avoidance of injury to the parietal pleura and inadvertent damage to the pulmonary parenchyma. When dissection is incomplete or inadequate, lysis of adhesions should be completed and performed with sharp dissection to avoid the formation of an alveolar-pleural fistula. With dense adhesions related to tumor invasion of the parietal pleura of the lung, complete pleurectomy with simultaneous segmental resection of the focally involved lung segment may be necessary. Repair of any parenchymal tears may be completed by stapling or suturing with 3-0 absorbable polypropylene suture after adequate deflation of the lung without injury. The incision is thereafter extended around the peripheral margins of the tumor mass through the intercostal muscles. The surgeon must be cognizant of ligation of the intercostal neurovascular bundles on the inferior margins of the rib with 2-0 silk suture ligatures. Upon entering the thorax, prior pleural adhesions created by radiation therapy and/or surgery should be sharply dissected and the lung mobilized. Attention must be focused on the avoidance of injury to the visceral pleura of the lung and inadvertent damage to the pulmonary parenchyma. Further extension of the medial cut with rib cutter to the third rib on its medial surface. Pectoralis muscle (cut) Rib (cut) Intercostal muscle (cut) Pericardium to initiating rib division with a rib cutter. Following completion of the entire incision, the surgeon should be cognizant to include all the punch biopsy sites to ensure negative surgical margin. When the tumor margin extends medially to the sternum, it may be necessary to utilize a sternal saw or osteotome to create a partial sternotomy up to and inclusive of the biopsied skin that establishes a clear surgical margin. The sternum thereafter may be partially resected, but diligence must be exercised to protect the pericardium, which may be centrally adherent to the investing parietal pleura of the sternum, secondary to irradiation. In all circumstances, the specimen should be resected en bloc, thus exposing the chest wall defect with the exposed, inflated, protuberant lung. Insufflation of the underlying lung following resection of tumor invasion requires visualization of alveolarparenchymal leak; repair must be instituted for closure of such leaks. If invasive disease is detected grossly or with biopsy, the well-exposed lung can then be managed by a wedge resection of the involved lung with a stapler. Leaking defects should again be oversewn and tested for air leaks prior to tube placement and chest closure. Prior to initiating chest wall reconstruction, one apical-posterior chest tube should be placed in the midaxillary line inferior to the defect. The second tube is placed posteriorly and positioned toward the lung apex for fluid and air collection. Smaller caliber tubes are generally sufficient to manage the resulting iatrogenic pneumothorax. This reconstructive sandwich should be layered such that the methyl methacrylate is interposed between two layers of the polypropylene mesh. Inset identifies the optional creation of the methyl methacrylate "sandwich," in which methyl methacrylate interposes between two mesh surfaces of nonabsorbable polypropylene mesh. The strut of this prosthesis is created with the folding in half of a large piece of polypropylene mesh to ensure coverage of the sandwich over the defect without undue tension. Suturing of the polypropylene mesh encircling the rib margin on its superior and inferior surface of the resection with creation of the planned suture knots external to the mesh with full-thickness purchase through the musculature of the chest wall. The prosthetic strut may be created with the folding in half of a larger piece of polypropylene mesh that ensures coverage of the sandwich over the defect without undue tension. With planning of surface area of the prosthetic strut to cover the defect, the mesh should be contoured beyond all margins of the resection such that it can be sutured to the resected rib edge. We prefer that the first layer of the mesh be sutured to the edges of the wound using nonabsorbable 0 or 1 polypropylene sutures. Care must be taken to avoid entrapping the intercostal neurovascular bundle while securing the mesh. The latter neurovascular bundle should have previously been ligated in isolated fashion. Following placement and completion of suturing of the methyl methacrylate "sandwich," reconstruction of the soft-tissue defect is initiated. Again, the most commonly utilized and versatile flap reconstruction of this area is the pedicled latissimus dorsi flap that is inclusive of a vascularized skin paddle. The omental flap is based upon the right gastroepiploic artery that is utilized for tissue coverage. Design of the most commonly utilized and versatile flap reconstruction as a pedicled latissimus dorsi flap. Note that the flap is inclusive of a vascularized skin panel in the central inner outline, and in which the planned latissimus flap B, together with the exposed latissimus muscle and skin panel, has been harvested. The omental flap approach by necessity enhances potential morbidity as it adds complexity to the chest wall defect with abdominal entry. Following division of the left gastroepiploic artery, vascular perforators (vasa brevia) to perfuse this arcade are ligated in continuity for revascularization purposes. Ligation and division of the vasa recta of the anterior and posterior omental leaves is performed using 3-0 nonabsorbable sutures. Mobilization of the omentum, together with the splenocolic ligament, and division from the inferior gastric surface from the gastrocolic ligament to the base of the right gastroepiploic artery. To maintain integrity of the vascular perfusion pedicle, the surgeon must be cognizant of inadvertent rotation of the omental pedicle and avoidance of vascular injury to the peripheral and central components of the pedicle. Placement of the optional split-thickness skin graft coverage of the pedicle, which has been inserted in the patient as visualized at the time of a postoperative visit. The inset flap should be closed in two layers inclusive of a deep dermal layer that is sutured with 3-0 absorbable sutures. Chest tube drains are essential to evacuate the pneumothorax created with thoracotomy in these patients. In addition, we prefer large defects have subcutaneous closedsuction drains around the soft-tissue reconstruction for avoidance of hematoma and seroma. Proper suction drainage on the catheters is essential for vacuum decompression of the pneumothorax created with opening of the chest. Pulmonary management should include preventative care for ventilator-associated pneumonia. The opened thorax requires closed-suction chest tubes to evacuate the pneumothorax. In addition, the large defects require subcutaneous closedsuction drainage for evacuation of hematoma and seroma in the reconstruction site. The placement of internal Doppler probes over the vascularized free- flap arterial blood flow provides continual monitoring of the patient. Because of the considerable pain experienced with division of the ribs, postoperative epidural pain control should be considered, together with systemic analgesics and sedation. Continual wound care and flap management are essential; monitoring for flap ischemia and necrosis are the requisite. Arterial supply can best be evaluated by an internal Doppler that is placed intraoperatively. However, the hand-held external Doppler is commonly utilized together with visual inspection of capillary refill. Standard criteria are utilized in the management of chest tubes for the timing of removal of these tubes and subcutaneous drains. Removal is dependent upon complete resolution of the pneumothorax and decreasing subcutaneous serous wound drainage. Complications have been reported in as many as as 40% of patients(1) and vary from 5% to 40%. The most common complications relate to wound dehiscence, separation and drainage, as well as pneumonia related to deficient pulmonary toilet. Pulmonary complications also include the risk of re-intubation, flail chest, and pleural infection. Wound complications include infection, delayed wound repair, and partial flap or skin-graft necrosis. The serious complications of advanced wound infection often require debridement of portions or all of the methyl methacrylate-polypropylene mesh repair and may include major portions of the reconstruction. Despite the significant morbidity associated with the resection, mortality for the procedure is less than 5%. The surgeon must have a low threshold to evaluate and treat suspected wound and pulmonary infections. Such procedures are regarded as highly mutilating interventions that harbor high morbidity and mortality. Moreover, the utility of plastic reconstruction of the full-thickness chest wall resection for recurrent disease is largely unknown and rarely utilized in surgical clinics. In this series, the cumulative 5-, 10-, and 15-year survival rates were 46%, 29%, and 22%, respectively (median survival 56 months). These reports suggest improvement in long-term palliation and potential cure for this select patient group with chest wall recurrence of breast carcinoma. Sine quo none to eligibility as candidate for chest wall resection is confirmation of the absence of systemic disease following staging. A team approach with plastic and thoracic surgeons is essential with the oncologic surgeon to allow tissue transfer with reconstruction. Confirmation of absence of skin/muscle involvement with "punch" biopsy technique enhances local control. Resections that extend beyond four ribs will routinely require rigid chest wall reconstruction. Natural history and management of isolated localregional recurrence following mastectomy. Surgical treatment of chest wall invasion due to the local recurrence of breast cancer. Reconstruction of complex chest wall defects by using polypropylene mesh and a pedicled latissimus dorsi flap: a 6-year experience. Results of chest wall resection for recurrent or locally advanced breast malignancies. Myocutaneous versus thoraco-abdominal flap cover for soft tissue defects following surgery for locally advanced and recurrent breast cancer. Treatment and outcome of patients with chest wall recurrence after mastectomy and breast reconstruction. Outcomes of locoregional recurrence after surgical chest wall resection and reconstruction for breast cancer. Full-thickness chest wall resection for recurrent breast carcinoma: an institutional review and meta-analysis. Vásconez Reconstruction following mastectomy was initially described for soft tissue coverage of the chest wall defect. During the 1940s, Meier described techniques to reconstruct the chest wall with local cutaneous flaps. Refinement of the reconstructive techniques and the implementation of multistaged procedures followed. Over the subsequent 60 years, chest wall and breast reconstruction has undergone tremendous change with regard to the variety and complexity of flaps employed to maximize efficacy and aesthetics. Currently, chest wall defects in breast cancer patients can be divided in to two subcategories-those defects that are secondary to surgical resection of the tumor and those changes that occur later as a result of radiation therapy. Before considering any option for chest wall or breast reconstruction, it is important to understand the extent to which the soft tissue is affected. It is particularly well suited in patients who have a skin deficit and who are not candidates for autologous breast reconstruction. The thoracoepigastric flap can be combined with breast reconstruction by using an expander/implant. The donor site morbidity is limited to an area along the inframammary fold, which can be hidden within the inframammary fold and under the bra. It can be particularly useful when the patient does have excess skin in the upper abdominal region. Typically, healthy patients, with few comorbidities, are candidates for more extensive breast reconstructive options. Currently, the latissimus dorsi myocutaneous flap, with an implant or one of the variants of the rectus abdominus flaps, is preferable to local skin flaps as it offers soft tissue coverage for the chest wall and soft tissue to facilitate recreation of the breast mound. Local skin, soft tissue flaps are not indicated for patients who are candidates for immediate reconstruction.

An example of the solute carrier transporters is nucleoside transports anxiety xanax and copd venlafaxine 150 mg buy with visa, which are responsible for the uptake of nucleosides anxiety symptoms stomach cheap 37.5 mg venlafaxine fast delivery, the precursors of nucleotides anxiety 8 year old daughter 75 mg venlafaxine purchase otc. Transporters can also be selective for different classes of substrates as is the case for the transporters of purine and pyrimidines anxiety zoning out buy cheap venlafaxine online. Because many transporters have nutrients as substrates anxiety symptoms flushed face cheap venlafaxine 150 mg, prodrug design is manipulated to mask the drug with nutrient moiety so as to initiate prodrug uptake through these transporters. Upon absorption, valacyclovir is rapidly converted to its parent drug acyclovir via esterase cleavage. Acyclovir is then free to enter the bloodstream, where it is taken up by cells via nucleoside transporters. Besides the obvious benefit of increased oral absorption, this method of drug delivery has been tailored to target cancer cells over expressing certain membrane transporters. Thus, prodrugs utilizing the membrane transporters may be afforded the luxury of an oral formulation, which is the gold standard of administration. Amino acid side chains could be varied to alter the physicochemical properties of prodrug. The broad specificity of these transporters for multiple substrates increases the potential flexibility in prodrug design. The disadvantage associated with this approach is that these transporters are also expressed in cells of the small intestine, kidney, bile duct, and pancreas. Another problem could arise if the prodrug upon absorption by the transporter is quickly converted to parent drug. Once this occurs, the parent drug will be passively distributed throughout the systemic circulation, which could in turn cause systemic toxicity. If the complex is not broken down in the lysosomes, it may be released from the lysosomal compartment in to the cytoplasm and may even escape from phagocyte causing a prolonged release systemic effect. Passive Targeting Passive targeting utilizes the natural or passive distribution characteristics of a carrier for drug targeting and no homing device is attached. Angiogenesis is induced in tumors to accommodate their ever-increasing demand for nutrition and oxygen as the tumor cells multiply and cluster together to reach the size of 2 to 3 nm. The perivascular cells and the smooth muscle layers are frequently absent or abnormal in the vascular wall. Tumor vessels develop wide lumens and the lymphatic drainage in tumor tissues becomes impaired. This results in to extensive leakage of blood plasma components such as macromolecules, nanoparticles, and lipidic particles in tumor tissues. These macromolecules and nanoparticles are retained in tumors due to the slow venous return in tumor tissues and poor lymphatic drainage. This phenomenon has been shown to achieve 10- to 50-fold (1%­5% and in some cases 20% of injected dose per gram of tumor) high local concentration of drugs in the tumor tissues than in normal tissues within 1 to 2 days of injection. These macromolecules or nanoparticles do not interact with tumor cells but strongly influence the drug biodistribution. The chemical nature of polymer, as well as shape and conformation in water, also influences its molecular size. Attachment to polymers results in to improved water solubility, prolonged stay in blood circulation, and reduced toxicities. Several passively targeted polymeric prodrugs are being evaluated in clinical trials75,76. Dendritic structures and particulate materials are also being explored for passive targeting of prodrugs. In another strategy, known as polymer-directed enzyme liposome therapy, liposomes. Several solid-particulate nanosuspensions are in the market; examples include sirolimus (Rapamune) (immunosuppressant, Wyeth) and aprepitant (Emend) (antiemetic, Merck). Liposomes Liposomes are vesicular structures based on one or more lipid bilayers encapsulating an aqueous core. These molecules spontaneously arrange themselves in water to give the thermodynamically most stable bilayer structures, where the hydrophilic head groups protrude outside in to the aqueous environment, and the hydrophobic chains orient themselves inward, away from water. The flat bilayers self-close in to concentric compartments around a central aqueous phase to give spherical liposomes with diameters in the range of 0. The liposomes are either unilamellar (one concentrically oriented bilayers around an aqueous core) or multilamellar (multitude of concentrically oriented bilayers around aqueous core). When the liposomes are multilamellar, water may be present in the aqueous core and also between the bilayers. Multilamellar vesicles are formed under low shear agitation with wide size distribution, display relatively low level of aqueous encapsulation, and have relatively short circulation half-lives. The smaller unilamellar vesicles on the other hand have narrow size distribution and therefore preferred for intravenous applications where a long circulation time is demanded. They are also useful for encapsulation of water-soluble drugs but suffer from tendency to aggregate in to larger liposomes. Multilamellar vesicles are readily converted to unilamellar vesicles by employing high shear processes such as sonication, homogenization, and extrusion. Liposomes are capable of incorporating both watersoluble (inside the aqueous core. They are biodegradable and nontoxic and proven to improve pharmacokinetic properties of the drugs. The drug release from the liposomes depends on the nature of phospholipids, composition of the liposomes, and hydrophilic or lipophilic properties of active ingredients. During the nebulization, the shear force generated by extrusion through the jet orifice reduces the liposome size to 0. Liposomes suffer from drawbacks such as (a) physical and chemical instability in liquid state; (b) low encapsulation efficiency for several drugs; and (c) challenging scale-up and 621 sterilization of the final formulation. Stability of liposomes is dependent on the lipid composition, storage conditions (light, oxygen, temperature, moisture), and stabilizers (cholesterol, -tocopherols and inert atmosphere) used, and in some liposomal formulations, physical and chemical stability can be improved by lyophilization. Micelles Surfactants molecules aggregate in aqueous solution to form micelles at certain concentrations and temperature62. Surfactants have a hydrophilic polar head group attached to a long-chain lipophilic (nonpolar) tail. Block copolymers comprising hydrophilic and hydrophobic segments are used to form polymeric micelles. Micelles are used for reducing the surface tension of water, increasing the miscibility of different solvent phases, and stabilizing the emulsions. These drug-loaded block copolymers form micelles in water with spherical core/shell structure with drugs present in hydrophobic core. Polymersomes and Dendrimers Polymersomes are polymer vesicles with a core-shell structure similar to liposomes. They are made of diblock copolymers, which contain hydrophilic and hydrophobic portions similar to phospholipids. Since polymersomes are stronger and more stable than liposomes, they display less deformation under load and slower rate of drug leakage. The degree of polymerization and melting temperature (Tg) of the polymer are varied to control the vesicle-like properties such as rigidity, thickness, and permeability. However, polymersomes are not biocompatible, their degradation products are usually toxic, and the drug release from these platforms is generally too slow. Drugs are incorporated in to the internal cavities or attached through the surface functional groups. The main use of polymeric dendrimers is to enhance aqueous solubility of the poorly soluble drugs. Lipoproteins, which are endogenous lipid carrier systems comprising a lipid core and a coat where apolipoprotein is found, have also been used for targeted drug delivery. The conventional prodrug design, where inactive prodrugs are transformed in to active drugs inside the cell. The most frequently used chemical linkages78 (bonds) in prodrug design are ester, carbonates, carbamates, amides, phosphates, and oximes. Linkages such as thioethers, thioesters, imines, and Mannich bases have also been used but to a lesser extent. The chemical groups that can produce the aforementioned linkages are carboxylic acid, hydroxyl, amine, phosphate/phosphonate, and carbonyl. Esters are the most common prodrug linkages constituting about half of marketed prodrugs. Once in the body, the ester bond is cleaved by ubiquitous esterases (blood, liver, and other organs) to release the active drug. Contrary to esters, phosphate ester prodrugs are prepared to enhance the aqueous solubility of parent drugs for achieving more favorable oral or parenteral administration. The amide prodrugs are relatively more stable in vivo and hydrolyzed to active drugs by enzymes such as carboxylesterases, peptidases, and proteases. Enzymatic cleavage is not the only mechanism available for prodrug activation; physicochemical environment at the target site. Activation is also achieved by incorporating self-immolative linker in the prodrug design. Attachment to promoiety through reversible bonds has been used to obtain prodrugs with improved lipophilicity or membrane permeability78,79. Prodrugs have been earlier referred to as reversible or bioreversible derivatives, latentiated drugs, and biolabile drug carrier conjugates but the term prodrug is now standard. In some cases, a prodrug may consist of two pharmacologically active drugs coupled together in to a single molecule so that each drug becomes a promoiety for the other; such derivatives are called codrugs. A bioprecursor prodrug is a prodrug that does not contain a carrier or promoiety but results from molecular modification of active agent itself (active metabolite). Soft drugs, which must not be confused with prodrug, are active drugs designed to undergo a predictable and controllable deactivation or metabolism in vivo after achieving the therapeutic effect. Prodrugs for improved ophthalmic (dipivefrin [propine] and latanoprost) and dermal (tazarotene) delivery and diseases such as Parkinson disease (levodopa), viral (pradefovir), asthma (bambuterol), hypercholesterolemia (simvastatin), and cancer. A few specific prodrug examples are discussed below to illustrate the salient features of conventional prodrug design. Enalapril is a prodrug used for lowering the blood pressure, congestive heart failure, and kidney problems. It is an ethyl ester prodrug of enalaprilat, which suffers from low oral bioavailability (36%­44%). Conversion to ester enhances the absorption from 53% to 74% and the prodrug is readily converted to active form by hydrolysis of ester in vivo, which inhibits angiostensin-converting enzyme. The conversion of capecitabine to active drug is achieved in three-steps: (a) a hepatic carboxylesterase converts it in to 5 -deoxy-5-fluorocytidine, (b) 5 -deoxy-5fluorocytidine is converted to 5 -deoxy-5-fluorouridine by cytidine deaminase enzyme in the liver/tumor, and (c) tumorassociated enzyme thymidine phosphorylase converts 5 deoxy-5-fluorouridine to 5-fluoruracil, which in turn is converted to 5 -fluoruridine or 5 -fluoro-2-deoxyuridine. Conventional prodrugs are associated with several limitations, most important being their nonspecific activation inside the body. Current prodrug designs are therefore highly focused on the development of targeted prodrugs, where tar- 623 geting is achieved by employing either active or passive targeting strategies described earlier (see section Targeted Drug Delivery). Carrier-linked design has been employed to obtain prodrug targeted to cell/tissue-specific antigens and receptors. A recently approved example in this category is gemtuzumab ozogamicin (Mylotarg, Wyeth)65. Following membrane transport, the active drug is released by intracellular hydrolysis. Controlled drug delivery should not be confused with prolonged or sustained drug delivery because the controlled drug delivery attempts to control drug level in the target tissues or cells, whereas the sustained drug delivery is restricted to maintaining therapeutic blood or tissue levels of drug for extended period of time. Prodrug activation of (a) enalapril, (b) simvastatin, (c) capecitabine, and (d) valacyclovir. Frequent dosing is therefore needed to maintain therapeutically effective plasma drug level, more so for drugs with short half-lives, which is likely to result in to toxic side effects and poor patient compliance. Using controlled drug delivery, which involves delivering drug either locally or systemically at a predetermined rate, undesirable fluctuation of drug levels in plasma can be avoided. Design- ing a controlled drug delivery system requires simultaneous consideration of several factors2b,3,80 such as the nature of disease and therapy (acute/chronic), drug property, route of drug administration, nature of delivery vehicle, mechanism of drug release, targeting ability, and biocompatibility. It is not easy to achieve all these in one system due to their extensive interdependency. Besides, reliability and reproducibility are also crucial to successful designing of delivery systems. The sawtooth kinetic profile obtained after normal dosing and optimum therapeutic profile obtainable with controlled-delivery devices. Ideally the controlled drug delivery system should be inert, biocompatible, mechanically strong, convenient for the patient, capable of achieving high drug loading, safe from accidental drug release, simple to administer and remove, and easy to fabricate and sterilize. Advantages of controlled drug delivery are that fluctuations in drug plasma level associated with conventional dosage forms are avoided and therapeutic drug concentration is maintained, which leads to more effective therapies with lesser side effects. While the therapeutic considerations are prime driving force for the development of drug delivery systems, there are economic considerations too. Repackaging the drug in a new delivery system allows the company to extend the patent life of its product. The disadvantages on the other hand are higher costs compared to conventional formulations, possible toxicity or nonbiocompatibility of the material used, and undesirable by-products. More importantly, many controlled drug delivery systems are invasive and require surgical intervention for their insertion and removal from the body. The drug is released at variable rates to match circadian rhythms or mimic natural biorhythms. It is characterized by an episodic increase in drug concentration followed by a "rest" period, where drug level falls below the therapeutic level. It may also be fluctuating or pulsatile (release pulses at predetermined lag times). Variable release is used in situations where changing level of response is needed. For example, in hypertension, blood pressure is lower in the night but increases in the early morning, and consequently maximum drug levels are needed in the early morning.

Syndromes

• Fever
• Drowsiness
• Seizures
• Reduced amount of urine
• Pain is severe.
• Brain infections (encephalitis, meningitis, herpes simplex infections)

These and other factors reviewed by Lees1 make it apparent that a pharmacist today must possess a sound knowledge of micromeritics anxiety symptoms go away buy cheap venlafaxine 150 mg online. Particle size and size distributions will be considered in this section; shape and surface area will be discussed subsequently anxiety symptoms help order 150 mg venlafaxine with visa. As the degree of asymmetry of particles increases anxiety chest pains 37.5 mg venlafaxine fast delivery, however anxiety symptoms or heart problems 75 mg venlafaxine free shipping, so does the difficulty of expressing size in terms of a meaningful diameter anxiety symptoms every day discount venlafaxine 37.5 mg amex. Recourse must be made to the use of an equivalent spherical diameter, which relates the size of the particle to the diameter of a sphere having the same surface area, volume, or diameter. Thus, the surface diameter, ds, is the diameter of a sphere having the same surface area as the particle in question. The diameter of a sphere having the same volume as the particle is the volume diameter, dv, whereas the projected diameter, dp, is the diameter of a sphere having the same observed area as the particle when viewed normal to its most stable plane. The size can also be expressed as the Stokes diameter, dst, which describes an equivalent sphere undergoing sedimentation at the same rate as the asymmetric particle. Invariably, the type of diameter used reflects the method employed to obtain the diameter. As will be seen later, the projected diameter is obtained by microscopic techniques, whereas the Stokes diameter is determined from sedimentation studies on the suspended particles. Particles having the size of coarser powders, tablet granulations, and granular salts fall within the sieve range. The approximate size ranges of particles in pharmaceutical dispersions are listed in Table 18­1. The sizes of other materials, including microorganisms, are given in Tables 18­2 and 18­3. The unit of particle size used most frequently in micromeritics is the micrometer, m, also called the micron, and equal to 10-6 m, 10-4 cm, and 10-3 mm. One must not confuse m with m, the latter being the symbol for a millimicron or 10-9 m. It is therefore necessary to know not only the size of a certain particle but also how many particles of the same size exist in the sample. Thus, we need an estimate of the size range present and the number or weight fraction of each particle size. This is the particle-size distribution, and from it we can calculate an average particle size for the sample. If a drug product formulator desires to work with particles of approximately uniform size. Such particles of uniform size3 are used in science, medicine, and technology for various diagnostic tests; as particle-size standards for particle analyzers; for the accurate determination of pore sizes in filters; and as uniformly sized surfaces upon which antigens can be coated for effective immunization. To compare these values with those from, say, a second batch of the same material, we 0. Refers to particle having average surface area Refers to particle having average weight and is related inversely to N, the number of particles per gram of material No practical significance nd 2 n nd 3 n 2 0 Arithmetic Surface Number Surface-number mean, dsn Volume-number mean, dvn 2. Edmundson5 derived a general equation for the average particle size, whether it be an arithmetic, a geometric, or a harmonic mean diameter: dmean = nd p+ f nd f 1/ p Some of the more significant arithmetic (p is positive) mean diameters are shown in Table 18­5. For a more complete description of these diameters, refer to the work of Edmundson. Such plots give a visual representation of the distribution that an average diameter cannot achieve. This is important because it is possible to have two samples with the same average diameter but different distributions. Moreover, it is immediately apparent from a frequency distribution curve what particle size occurs most frequently within the sample. An alternative method of representing the data is to plot the cumulative percentage over or under a particular size versus In equation (18­1), n is the number of particles in a size range whose midpoint, d, is one of the equivalent diameters mentioned previously. The term p is an index related to the size of an individual particle, because d raised to the power p = 1, p = 2, or p = 3 is an expression of the particle length, surface, or volume, respectively. The value of the index p also decides whether the mean is arithmetic (p is positive), geometric (p is zero), or harmonic (p is negative). For a collection of particles, the frequency with which a particle in a certain size range occurs is expressed by nd f. When the frequency index, f, has values of 0, 1, 2, or 3, then the size frequency distribution is expressed in terms of the total number, length, surface, or volume of the particles, respectively. The data are plotted as a bar graph or histogram, and a superimposed smooth line or frequency curve is shown drawn through the histogram. A sigmoidal curve results, with the mode being that particle size at the greatest slope. As the name implies, the distribution is symmetric around the mean, which is also the mode. When the logarithm of the particle size is plotted against the cumulative percent frequency on a probability scale, a linear relationship is observed. Such a linear plot has the distinct advantage that we can now characterize a lognormal distribution curve by means of two parameters-the slope of the line and a reference point. Knowing these two the statistic is the standard deviation of a very large number of measurements approximating the total population or universe of particles. Because the particle sample measured in pharmaceutical systems ordinarily is small relative to the universe, the statistic used to express the variability of a sample is usually written as s rather than. Authors of works on particle-size analysis frequently do not make a distinction between and s, a practice that is followed in this chapter. The reference point used is the logarithm of the particle size equivalent to 50% on the probability scale, that is, the 50% size. The slope is given by the geometric standard deviation, g, which is the quotient of the ratio (84% undersize or 16% oversize)/(50% size) or (50% size)/(16% undersize or 84% oversize). The dissolution of the tolbutamide agglomerates followed the Hixon­Crowell cube root equation, as did the dissolution rate of tolbutamide crystals alone. Frequency distribution plot of the data in Table 18­6 showing log-normal relation. Number and Weight Distributions the data in Table 18­6 are shown as a number distribution, implying that they were collected by a counting technique such as microscopy. Although this can be achieved by using a technique such as sedimentation or sieving, it will be more convenient, if the number data are already at hand, to convert the number distribution to a weight distribution and vice versa. Provided the general shape and density of the particles are independent of the size range present in the sample, an estimate of the weight distribution of the data in Table 18­6 can be obtained by calculating the values shown in columns 9 and 10. The significant differences in the two distributions are apparent, even though they relate to the same sample. For this reason, it is important to distinguish carefully between size distributions on a weight and a number basis. Customarily, the prime is dropped because the value is independent of the type of distribution. The geometric mean diameter (the particle size at the 50% probability level) on a weight basis, dg, is 10. In addition, a particular average can be readily computed by use of the relevant equation. Assume that the particles are spheres, the volume of 3 a single particle is dvn /6, and the mass (volume × density) 3 is dvn /6 g per particle. Only those that are widely used in pharmaceutical practice and are typical of a particular principle are presented. For a detailed discussion of the numerous methods of particle size analysis, consult the work by Edmundson5 and Allen10 and the references given there to other sources. The methods available for determining the size characteristics of submicrometer particles were reviewed by Groves. Although the microscope allows the observer to view the actual particles, the results obtained are probably no more "direct" than those resulting from other methods because only two of the three particle dimensions are ordinarily seen. The sedimentation methods yield a particle size relative to the rate at which particles settle through a suspending medium, a measurement important in the development of emulsions and suspensions. The measurement of particle volume, using an (18­2) to readily obtain dg knowing dg and g. Approximate size ranges of methods used for particle-size and specific-surface analysis. Thus, in all these cases, the size may or may not compare with that obtained by the microscope or by other methods; the size is most directly applicable to the analysis for which it is intended. Optical Microscopy It should be possible to use the ordinary microscope for particle-size measurement in the range of 0. According to the microscopic method, an emulsion or suspension, diluted or undiluted, is mounted on a slide or ruled cell and placed on a mechanical stage. The microscope eyepiece is fitted with a micrometer by which the size of the particles can be estimated. The field can be projected on to a screen where the particles are measured more easily, or a photograph can be taken from which a slide is prepared and projected on a screen for measurement. The particles are measured along an arbitrarily chosen fixed line, generally made horizontally across the center of the particle. The line can be drawn in any direction but must be in the same direction for all particles measured. It is the diameter of a circle with the same area as that of the particle observed perpendicular to the surface on which the particle rests. Electronic scanners have been developed to remove the necessity of measuring the particles by visual observation. Prasad and Wan14 used video recording equipment to observe, record, store, and retrieve particle-size data from a microscopic examination of tablet excipients, including microcrystalline cellulose, sodium carboxymethylcellulose, sodium starch glycolate, and methylcellulose. A general diagram providing definitions of the Feret, Martin, and projected diameters. The video recording technique was found to be simple and convenient for microscopic examination of excipients. A disadvantage of the microscopic method is that the diameter is obtained from only two dimensions of the particle: length and breadth. In addition, the number of particles that must be counted (300­500) to obtain a good estimation of the distribution makes the method somewhat slow and tedious. Nonetheless, microscopic examination (photomicrographs) of a sample should be undertaken even when other methods of particle-size analysis are being used, because the presence of agglomerates and particles of more than one component may often be detected. Sieves are generally used for grading coarser particles; if extreme care is used, however, they can be employed for screening material as fine as 44 m (No. Sieves produced by photoetching and electroforming techniques are available with apertures from 90 m to as low as 5 m. Pharmacopeia for testing powder fineness, a mass of sample is placed on the proper sieve in a mechanical shaker. The powder is shaken for a definite period of time, and the material that passes through one sieve and is retained on the next finer sieve is collected and weighed. Another approach is to assign the particles on the lower sieve with the arithmetic or geometric mean size of the two screens. Arambulo and Deardorff15 used this method of size classification in their analysis of the average weight of compressed tablets. Frequently the powder is assigned the mesh number of the screen through which it passes or on which it is retained. King and Becker16 expressed the size ranges of calamine samples in this way in their study of calamine lotion. When a detailed analysis is desired, the sieves can be arranged in a nest of about five with the coarsest at the top. A carefully weighed sample of the powder is placed on the top sieve, and after the sieves are shaken for a predetermined period of time, the powder retained on each sieve is weighed. Assuming a log-normal distribution, one plots the cumulative percent by weight of powder retained on the sieves on the probability scale against the logarithm of the arithmetic mean size of the openings of each of two successive screens. According to Herdan,17 sieving errors can arise from a number of variables including sieve loading and duration and intensity of agitation. Care must be taken, therefore, to ensure that reproducible techniques are employed so that different particle-size distributions between batches of material are not due simply to different sieving conditions. The equation holds exactly only for spheres falling freely without hindrance and at a constant rate. The law is applicable to irregularly shaped particles of various sizes as long as one realizes that the diameter obtained is a relative particle size equivalent to that of sphere falling at the same velocity as that of the particles under consideration. The particles must not be aggregated or clumped together in the suspension because such clumps would fall more rapidly than the individual particles and erroneous results would be obtained. The proper deflocculating agent must be found for each sample that will keep the particles free and separate as they fall through the medium. In other words, the rate of sedimentation of a particle must not be so rapid that turbulence is set up, because this in turn will affect the sedimentation of the particle. Whether the flow is turbulent or laminar is indicated by the dimensionless Reynolds number, Re, which is defined as Re = v d0 0 (18­7) where the symbols have the same meaning as in equation (18­ 5). On this basis, the limiting particle size under a given set of conditions can be calculated as follows. What is the size of the largest particle that will settle without causing turbulence Andreasen apparatus for determining particle size by the gravity sedimentation method. Principal among these are the pipette method, the balance method, and the hydrometer method. Only the first technique is discussed here because it combines ease of analysis, accuracy, and economy of equipment. It usually consists of a 550 mL vessel containing a 10 mL pipette sealed in to a ground-glass stopper. When the pipette is in place in the cylinder, its lower tip is 20 cm below the surface of the suspension.

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