By C. Zapotek. Colgate University. 2018.
Their clearance values and target steady-state plasma concentrations have been taken from the literature generic cytotec 100mcg with mastercard, and it has been assumed that order cytotec 200 mcg with visa, for each compound buy cytotec 100mcg overnight delivery, a steady-state delivery rate (k ) intoo the body of 25 µg cm−2 hr−1 can be achieved. Of course, for many compounds, such a high flux (which is typical only for such rapidly permeating drugs as nitroglycerin and nicotine) is completely unrealistic. As can be seen by the resulting estimations of the minimum patch area (Amin) necessary to arrive at the target blood concentration (determined using Equations 8. Consequently, considerable effort is being directed at approaches to increase Jmax, i. Possibilities include: 209 • increasing the amount of drug in the vehicle and hence increasing the total delivered dose from a single application (but this does not necessarily mean that the rate of absorption is enhanced); • increasing drug solubility in the stratum corneum, i. It should: • elicit no pharmacological effect; • be specific in its action; • act quickly, with a predictable duration, and its action should be reversible; • be chemically and physically stable, and be compatible with all components of the drug delivery system; • be odorless and colorless; • be non-toxic, non-allergenic and non-irritating. It remains to be seen to what extent the limitations can be relaxed for a chemical promoter to be acceptable (to patients and to the regulatory authorities). Enhancers include a wide range of chemical entities that increase skin permeability (Figure 8. Outstanding issues which need to be resolved include questions about the mechanism of action of the different enhancers in use at present, and the reversibility of their effects in vivo. Regulatory approval within the United States for an enhancer known as Azone proved to be extremely difficult because, as a new chemical developed specifically for skin permeation enhancement, it was subjected to an examination almost as detailed as that customary for a new therapeutic agent. Needless to say, this is an expensive path to follow for what is essentially a low-concentration excipient in a formulation and, as a result, the strategy now is to identify already-known and in-use materials (or combinations thereof) which have enhancing capabilities. These “generally regarded as safe” components offer a much easier regulatory path than that reserved for a new chemical entity. Practically speaking, the potential difference across the skin provides a force in addition to the passive flow of solute induced by the concentration gradient (Figure 8. The isoelectric point of human skin is around pH 4 which implies that skin, under normal physiological conditions, supports a net negative charge. Hence, the skin is permselective to the passage of positive ions and, as a result, more momentum is transferred to the solvent in the direction of cation flow. Thus, iontophoresis also induces a convective flow (called electroosmosis) whereby the flux of both charged and uncharged species can be significantly enhanced over passive levels. Thus, all things being equal, positively charged compounds are delivered more efficiently from the anode than negatively charged compounds from the cathode than neutral substances from the anode. Predictably, there appears to be an inverse dependence of iontophoretic permeability on molecular weight. Whether there is an “upper limit” has not been determined, although delivery of quite large molecules (e. In practical terms, this means that the viability of delivery as a function of increasing molecular weight is dependent upon a concomitant increase in pharmacological potency (i. It should also be noted that, with respect to peptide transport, amino acid sequence and conformation are potentially important variables that can dramatically impact upon iontophoretic delivery. From a practical standpoint, iontophoresis offers, under ideal circumstances, the singular advantage that it is an enhancement procedure which acts on the drug rather than on the skin (as is the case with chemical enhancers, for example). Typically, a constant or pulsed direct current is applied between the two electrodes placed on the skin surface. The current determines the charge flowing in the circuit, and hence the number of ions moving across the skin—if the current is doubled, the number of ions transferred across the skin is increased by a factor of two; if the current is turned off, ion flow through the membrane should return to the passive (i. Even though the drug may only carry a fraction of the total charge flowing (or may even be primarily transported by electroosmosis), its flux will be directly proportional to the applied current density, and hence highly controlled and controllable. Ag/AgCl), which do not lead to the hydrolysis of water at the potentials used, are preferred. Acceptable levels of current density and total current are dependent upon the treatment area and duration of current passage. The ionic composition of the delivery system should be selected so that there is minimum competition with the drug to carry charge across the skin (i. However, there must be sufficient electrolyte present to sustain current passage and to satisfy the electrochemical requirements of the electrodes. And, as mentioned above, in the case of larger compounds, for which electroosmosis may be the major mechanism of transport, different formulation strategies may be required.
This phosphorylation is the critical event that removes them from the secretion pathway and directs them to lysosomes 200 mcg cytotec with visa. Genetic defects affecting this phosphory- lation produce I-cell disease in which lysosomal enzymes are released into the extracellular space discount cytotec 100 mcg with visa, and inclusion bodies accumulate in the cell purchase cytotec 200mcg free shipping, compromising its function. It has a somewhat unique primary structure in that much of its length is com- posed of a repeating tripeptide Gly-X-Y-Gly-X-Y-etc. Important points about collagen synthesis are summarized below and in Figure 1-4-11. Three pro-a chains assemble to form a triple helical structure (procollagen), which can now be transferred to the Golgi. The propeptides are cleaved from the ends of pro collagen by proteases to form collagen molecules (also called tropocollagen). Like osteogenesis deficiency Poor wound healing imperfecta, these syndromes I Poor bone development are a result of locus Osteogenesis Mutations in collagen Skeletal deformities I heterogeneity in which imperfecta genes Fractures, blue sclera defects in several different genes (loci) can result in Ehlers- Danlos Mutations in collagen Hyperextensible, fragile skin I similar symptoms. Menkes Disease A 4-month-old infant who failed to grow and appeared to be mentally retarded was brought to the clinic for testing. A blood test showed that the infant had low serum ceruloplasmin and only 10% of normal serum copper levels. Common with Ehlers-Danlos diseases, Menkes disease has a symp- tomology due, in part, to weak collagen. Copper can be absorbed into the mucosal cell, but it cannot be transported into the bloodstream. Consequently, an affected individual will have severe copper deficiency and all copper- requiring enzymes will be adversely affected. Lysyloxidase requires copper and plays a direct role in collagen formation by catalyzing the cross-linking of collagen fibrils. A deficiency in the activity of this enzyme and other copper-dependent enzymes would be directly respon- for the described symptoms in this infant. For each mutation described in the questions below, choose the most closely related sequence change in the options above. During ~-globin synthesis in normal reticulocytes the sequence his-arg-pro occurs at position 165-167. How many high-energy phosphate bonds are required to insert these three amino acids into the ~-globin polypeptide during translation? A nasopharyngeal swab obtained from a 4-month-old infant with rhinitis and paroxysmal coughing tested positive upon culture for Bordetella pertussis. A 25-month-old Caucasian girl has coarse facial features and gingival hyperplasia and, at 2 months of age, began developing multiple, progressive symptoms of mental retarda- tion, joint contractures, hepatomegaly, and cardiomegaly. Levels of lysosomal enzymes are elevated in her serum, and fibroblasts show phase-dense inclusions in the cytoplasm. Which of the following enzyme deficiencies is most consistent with these observations? Parahemophilia is an autosomal recessive bleeding disorder characterized by a reduced plasma concentration of the Factor V blood coagulation protein. Deficiency arises from a 12 base-pair deletion in the Factor V gene that impairs the secretion of Factor V by hepa- tocytes and results in an abnormal accumulation of immunoreactive Factor V antigen in the cytoplasm. Collagen, the most abundant protein in the human body, is present in varying amounts in many tissues. If one wished to compare the collagen content of several tissues, one could measure their content of A. A 6-month-old infant is seen in the emergency room with a fractured rib and subdural hematoma. Respiratory tract infections caused by Pseudomonas aeruginosa are associated with the secretion of exotoxin A by this organism. Stimulation of histamine release 66 meClieal • i I,I The Genetic Code, Mutations, and Translation I: 12. The nucleotide sequences of codons 506-511 in this region of the normal and mutant alleles are compared below. Deletion of a phenylalanine residue causing a change in the C-terminal sequence D.
The presence of a positive stress test or continued high suspicion for coronary artery disease even after a negative stress test usually 298 A buy cytotec 100mcg free shipping. All patients in whom ischemic heart disease is suspected ultimately undergo this test to determine the pres- ence or absence of coronary artery or valvular heart disease order 200mcg cytotec overnight delivery. Therapeutic Intervention and Results Ischemic Heart Disease At the present time cheap cytotec 200 mcg mastercard, there are three classiﬁcations of therapy available to patients with ischemic heart disease. These are referred to as medical therapy, percutaneous angioplasty, and coronary bypass surgery. Decisions regarding treatment must be individualized and based on symptoms, anatomy, and risks of the selected therapy. The classic approach to medical therapy for ischemic heart disease is a three-pronged approach to decrease oxygen demand by the heart and includes beta-blockers, nitrates, and calcium channel blockers. As noted earlier, the prime cause of angina pectoris is the mismatch of oxygen demand and oxygen supply to the heart. Oxygen demand of the heart is determined by three major factors: (1) heart rate; (2) wall tension; and (3) to a lesser extent, the level of contractility of the heart. Wall tension is determined by Laplace’s law of the heart, in which wall tension is directly related to pressure and volume and inversely related to the wall thickness of the chamber involved: T = P ¥ R/2h where T is the wall tension, P is the chamber pressure, R is the chamber radius, and h is the wall thickness. The goal of their use is ﬁrst to minimize increases in heart rate due to response to physical and emotional demands and second to decrease myocardial contractility. Nitrates decrease the preload through venous dilatation and relaxation of the capacitance vessels. Sublingual nitroglycerin, nitroglycerin paste, and other longer acting nitrates are included in this category. Calcium channel blockers provide afterload reduction (and thus, decreased wall tension) by relaxing the smooth muscle of peripheral vessels and pre- venting coronary spasm. In theory, only after a patient fails to respond to the simultaneous use of all three modes of therapy at maximal tolerated doses is a patient considered to have “failed medical therapy. Using techniques similar to cardiac catheterization, a guidewire is directed across and through the coro- nary lesion under ﬂuoroscopic control. The balloon is inﬂated, compressing the lesion against the walls of the vessel, or an atherectomy is performed with actual removal of mater- ial from the wall of the vessel. The advantage of these procedures (when they are appropriate) is that the patient suffers little in the way of disability and the hospital- ization usually is quite short. In these situations, the surgical results are not as good as for elective surgery; perioperative myocar- dial infarction and mortalities both are higher. Recently, intracoronary stents made of ﬁne metal mesh have been developed, and, based on limited results to date, seem to increase the likelihood of longer patencies following angioplasty as well as to lower the risk for emer- gency surgery at the time of the procedure. Irradiated and drug- eluding stents are now being tested and seem to prolong the patency even further. Certain anatomic situations (left main disease, left main equivalent, and three-vessel disease with decreased ven- tricular function) may warrant surgery even in the absence of symp- toms because of the large amount of myocardium in jeopardy and the recognized high mortality risk without treatment (including sudden death). All patients with these conditions are likely to beneﬁt from surgery either with relief of symptoms, prevention of myocar- dial infarction, or prolongation of life. Guidelines for coronary artery bypass surgery, executive summary and recommendations. Spotnitz going surgery for complications of myocardial infarction (acute mitral regurgitation, ventricular septal defect, or free rupture of the heart) or for patients undergoing elective valve replacement procedures with critical vessel occlusions. Patients with limited life expectancy from other diseases (especially malignancies), the very elderly, or the physically impaired might not be considered surgical candidates based on asso- ciated physical conditions. Diseases of the Thoracic Aorta Decisions regarding treatment of patients with aortic aneurysms are dependent on the risk/beneﬁt ratio to the patient. Symptomatic patients have a mean survival of approximately 2 years following onset of the symptoms. The majority of time, however, the surgeon is con- fronted with a patient without symptoms found to have an aneurysm on a routine chest x-ray or other study. Here, the greatest risk to the patient is rupture of the aorta, which is more likely to occur the greater the size of the aorta. Aortic dissection is treated in a different manner because of the acuteness of the situation. Regardless of the type of dissection (Stan- ford A or B), initial emergent therapy is medical, with a goal of con- trolling the patient’s symptoms, heart rate, and blood pressure. Following beta-blockade, blood pressure control is obtained using intravenous nitroprusside of nitroglycerin.
This sector soon attracted the attention of pharmaceutical entrepreneurs who saw opportunities for specialist formulation companies discount 200mcg cytotec amex. By the late 1970s there were a number of such companies in operation order cytotec 100 mcg with amex, including Alza purchase cytotec 100mcg mastercard, Elan, Eurand and Pharmatec International. Typically, there would be a development fee for such work, paid in stages as the project reached successive goals; finally, the client would either pay the developer royalties on the sales of the successful formulation, or subcontract production of the finished product to the advanced drug delivery company. These types of arrangements are still the basis for most development work in the advanced drug delivery sector carried out on behalf of pharmaceutical clients by specialist companies. Some of the early entrants into this field have expanded their activities into delivery routes other than their original core technology, so that they can offer solutions in the transdermal, inhalation and other fields as well as oral formulations. This is true of Alza, Elan and 3M, the latter being something of a hybrid since it is also a pharmaceutical company in the conventional sense. By contrast, some companies in this field are linked to specific routes of administration; Inhale Therapeutic systems, as its name implies, focuses on inhalation technology, while Pharmatec International, one of the oldest-established advanced drug delivery concerns, remains committed to the oral route. Drug delivery technology demands continual innovation in order to meet increasingly complex clinical demands and accommodate the needs of sophisticated new drugs. This places a heavy burden on existing specialist companies in terms of R&D commitment; it has led to the birth of a considerable number of small, research-driven concerns, often built around pharmaceutical specialists and teams from academia or the formulation departments of major pharmaceutical companies. Like companies in the biotechnology sector, these new ventures are set up to develop and exploit specific technologies, but their path to financial self- sufficiency is often shorter than that of a typical new biotech venture, because the regulatory hurdles are fewer when a new chemical entity is not involved. Here, the underlying technology is so new that it cannot even be described as “pharmaceutical” in any conventional sense. Likewise, the delivery technology is pushing back the boundaries of human knowledge, exploring the use of viruses as carriers for the genetic material, as well as other vehicles including liposomes. Since this applied research is, unusually, going hand-in-hand with fundamental research into the nature of the biological mechanisms involved, the development timetable is an extended one. In summary, the current structure of the advanced drug delivery industry is a complex one, embracing specialist companies which offer off-the-shelf and custom-developed delivery systems, some involved in a range of delivery routes, others concentrating on a single route of administration. There are leading-edge research teams in areas such as gene therapy, while some pharmaceutical concerns still maintain their own specialist advanced drug delivery formulation units developing essentially pharmaceutical solutions to formulation problems. What major contribution have advanced drug delivery systems made to anti-inflammatory drug therapy? Discuss the importance of the developing world as a market for advanced drug delivery systems. Systems are diversely referred to as “controlled release”, “sustained release”, “zero-order”, “reservoir”, “monolithic”, “membrane-controlled”, “smart”, “stealth” etc. Unfortunately, these terms are not always used consistently and, in some cases, may even be used inaccurately. For clarity and consistency, some common terms used in this book are defined as follows: • Prolonged/sustained release: the delivery system prolongs therapeutic blood or tissue levels of the drug for an extended period of time. Conventional drug delivery systems are simple oral, topical or injection formulations. Also, rate-control and drug targeting are treated as two separate issues in this book and are dealt with in detail in Chapters 4 and 5 respectively. Although there are literally hundreds of commercial products based on controlling drug release rate from delivery systems, there are in fact only a small number of mechanisms by which drug release rate is controlled: • Diffusion-controlled release mechanisms • Dissolution-controlled release mechanisms 57 Figure 3. If the drug concentration gradient remains constant, for example where solid drug particles are present and constant dissolution maintains the concentration of the drug in solution, the rate of drug release does not vary with time and zero- order controlled release is attained (see Chapter 4 and Figure 4. Diffusion-controlled reservoir devices are used in a wide variety of routes including those shown in Table 3. Regardless of a drug’s physical state in the polymeric matrix, such devices do not usually provide zero-order drug release properties. This is because as the drug molecules at the surface of the device are released, those in the centre of the device have to migrate longer distances to be released, which takes a longer time. This increased diffusion time results in a decrease in the release rate from the device with time. Generally the rate of release is found to decrease in proportion to the square root of time (“M t1/2” kinetics; see Chapter 4 and Figure 4.
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