By D. Peratur. Eastern Michigan University. 2019.
One regimen may succeed another The antitubercular regimen should be modified if local testing shows resistance to one or more of these drugs cheap tadora online american express. Be- Streptomycin was the first drug recognized as cause these drugs have a greater incidence of effective in treating tuberculosis cheap tadora 20mg without prescription. Of these two drugs purchase generic tadora, ofloxacin mycin is excreted primarily by the kidneys as is more potent and may be an initial choice in unchanged drug. These drugs are administered tomycin well, but those receiving large doses orally and are generally well tolerated. However, resistance to fluoroquinolones devel- ops rapidly when these drugs are used alone or in insufficient doses. At usual dos- es, ethambutol and isoniazid are tuberculostatic, meaning that they inhibit the growth of M. In contrast, rifampin is tuberculocidal, meaning that it destroys the mycobacteria. Be- cause bacterial resistance to isoniazid and rifampin can develop rapidly, they should always be used with other antitubercular drugs. Antireplication station The exact mechanism of action of ethambutol remains unclear, but it may be related to inhibition of cell metabolism, arrest of multiplication, and cell death. It can Although isoniazid’s exact mechanism of action isn’t known, the take as many as five drug is believed to inhibit the synthesis of mycolic acids, impor- or six drugs to wipe tant components of the mycobacterium cell wall. The drug is effective primarily in replicating bacteria, but may have some effect on resting bacteria as well. Acid based The exact mechanism of action of pyrazinamide isn’t known, but the antimycobacterial activity appears to be linked to the drug’s conversion to the active metabolite pyrazinoic acid. Pyrazinoic acid, in turn, creates an acidic environment where mycobacteria can’t replicate. Pharmacotherapeutics Isoniazid usually is used with ethambutol, rifampin, or pyrazi- namide. Isoniazid is typically given orally, but may be given intravenously, if necessary. It combats many gram-positive and some gram-negative bacteria, but is seldom used for nonmycobacterial infections because bacterial resistance develops rapidly. It’s used to treat asymptomatic carriers of Neisseria meningitidis when the risk of meningitis is high, but it isn’t used to treat N. Adverse reactions to antitubercular drugs Here are common adverse reactions to antitubercular drugs. Pyrazinamide Liver toxicity is the major limiting adverse reac- Isoniazid Rifampin is tion. Antimycotic drugs Antimycotic, or antifungal, drugs are used to treat fungal infec- tions. The major antifungal drug groups include: • polyenes • fluorinated pyrimidine • imidazole • synthetic triazoles • glucan synthesis inhibitors • synthetic allylamine derivatives. Ampho- tericin B’s potency has made it the most widely used antimycotic drug for severe systemic fungal infections. It’s available in several forms, including lipid-based preparations that may decrease renal or systemic toxicity. Nystatin is used only topically or orally to treat local fungal infections because it’s extremely toxic when ad- ministered parenterally. Available as miconazole or miconazole nitrate, this imidazole derivative is used to treat local fungal infections, such as vagi- Clotrimazole nal and vulvar candidiasis, and topical fungal infections such as An imidazole derivative, clotrimazole is used: chronic candidiasis of the skin and mucous membranes. To prevent a relapse, griseofulvin therapy must continue until the fungus is eradicated and the infected skin or nails are re- placed. A license to kill Amphotericin B usually acts as a fungistatic drug (inhibiting fun- gal growth and multiplication), but can become fungicidal (de- stroying fungi) if it reaches high concentrations in the fungi. Nystatin binds to sterols in fungal cell membranes and alters Memory the permeability of the membranes, leading to loss of cell compo- jogger nents. Nystatin can act as a fungicidal or fungistatic drug, depend- If a drug is ing on the organism present. It’s never used for noninvasive forms of fungal disease be- and multiplication— cause it’s highly toxic. It’s usually the drug of choice for severe in- stasis is a Greek fections caused by Candida, Paracoccidioides brasiliensis, Blas- term for “halting. It’s also effective against As- pergillus fumigatus, Microsporum audouinii, Rhizopus, Candi- da glabrata, Trichophyton, and Rhodotorula. Last-ditch effort Because amphotericin B is highly toxic, its use is limited to the pa- tient who has a definitive diagnosis of life-threatening infection and is under close medical supervision. Differ- ent forms of nystatin are available for treating different types of candidal infections. Topical nystatin is used to treat candidal skin or mucous membrane infections, such as oral thrush, diaper rash, vaginal and vulvar candidiasis, and candidiasis between skin folds. Drug interactions Nystatin doesn’t interact significantly with other drugs, but am- photericin B may have significant interactions with many drugs. Amphotericin B preparations must be mixed with dextrose 5% in water; they can’t be mixed with saline It can get under your solution. Kidney concerns Up to 80% of patients may develop some de- gree of kidney toxicity, causing the kidneys to lose their ability to concentrate urine. Flucytosine Flucytosine is the only antimetabolite (a substance that closely re- sembles one required for normal physiologic functioning and that exerts its effect by interfering with metabolism) that acts as an an- timycotic. It’s a purine and pyrimidine inhibitor that’s used primar- ily with another antimycotic drug, such as amphotericin B, to treat systemic fungal infections. Pharmacodynamics Flucytosine penetrates fungal cells, where it’s converted to its ac- tive metabolite fluorouracil. Standing alone Flucytosine can be used alone to treat candidal infections of the Adverse lower urinary tract because it reaches a high urinary concentra- tion. Hematologic, kidney, and liver including: function must be closely monitored during flucytosine therapy be- • confusion cause of the drug’s serious risk of toxicity. Pharmacodynamics Within the fungal cells, ketoconazole interferes with sterol synthe- sis, damaging the cell membrane and increasing its permeability. This leads to a loss of essential intracellular elements and inhibi- tion of cell growth. Can inhibit or kill Ketoconazole usually produces fungistatic effects, but can also produce fungicidal effects under certain conditions. Pharmacotherapeutics Ketoconazole is used to treat topical and systemic infections caused by susceptible fungi, which include dermatophytes and most other fungi. Drug interactions Ketoconazole may have significant interactions with other drugs. If the patient must take these drugs, delay administration of ketoconazole by at least Adverse 2 hours. Fluconazole belongs to a class of synthetic, broad-spectrum triazoles and is also referred to as a bistriazole antimycotic drug. Itraconazole and voriconazole also belong to the synthetic tri- azole class of drugs. They inhibit the synthesis of ergosterol, a vi- tal component of fungal cell membranes.
Clinically important drug interactions • Drugs that increase effects/toxicity of calcium blockers: cimet- idine buy 20 mg tadora otc, β blockers buy tadora overnight delivery, cyclosporine buy 20mg tadora visa. Impaired renal function prolongs duration of action and increases tendency for toxicity. If anginal pain is not reduced at rest or during effort, reassess patient as to medication. If reepithelialization has not occurred in 21 days, other therapy should be considered. Adverse reactions • Common: lacrimation, irritation, infection of the conjunctiva. Editorial comments • May be administered together with topical gentamicin, eryth- romycin, and chloramphenicol. Mechanism of action: Disrupts cell division in metaphase by inhibition of microtubule formation. Warnings/precautions • Use with caution in patients with decreased bone marrow reserve, liver disease. Decrease doses in patients receiving other chemotherapy or with recent radiation therapy. Advice to patient • Use two forms of birth control including hormonal and barrier methods. Clinically important drug interaction • Drugs that increase effects/toxicity of vinblastine: antineo- plastic agents (cause bone marrow suppression), mitomycin (bronchospasm), erythromycin, ritonavir. If a medication-induced neuropathy is suspected, discontinue treatment immediately. Treat with peroxide, tea, topical anesthetics such as benzocaine or lidocaine, or antifungal drug. This toxic effect may occur within a few minutes of mitomycin C administration or may occur up to 2 weeks following administration of a single dose of mitomycin. Signs and symptoms include peripheral neuropathy, headache, confusion, urinary retention, and seizures. Mechanism of action: Inhibits synthesis of hepatic vitamin K-dependent clotting factors. Contraindications: Pregnancy, hemorrhagic disorders, hemo- philia, blood dyscrasias, thrombocytopenia purpura, malignant hypertension, recent surgery (eg, brain, eye), head injury, threatened abortion, spinal puncture, hypersensitivity to war- farin. Advice to patient • Carry identification card at all times describing disease, treatment regimen, name, address, and telephone number of treating physician. Editorial comments: All patients receiving an oral anticoagulant must be under close medical supervision. Laboratory facilities must be available to monitor therapy; personnel must know how to treat the hemorrhagic patient. Mechanism of action: Blocks leukotriene D4 and E4, reducing bronchospasm and inflammation. Contraindications: Hypersensitivity to zafirlukast, acute attack of asthma, status asthmaticus. Clinically important drug interactions • Drugs that decrease effects/toxicity of zafirlukast: erythromycin, theophylline, aspirin, magnesium or aluminum-containing antacids. Parameters to monitor: Signs and symptoms of asthma: Monitor respiratory rate, pulmonary function and oxygen saturation. Adjustment of dosage • Kidney disease: Creatinine clearance >40 mL/min: normal dose; creatinine clearance 10–40 mL/min: 0. Contraindications: Hypersensitivity to zalcitabine, coadminis- tration with other pancreatoxic agents (eg, pentamidine). Warnings/precautions • Use with caution in patients with peripheral neuropathy, kidney disease, heart failure, history of pancreatitis. Clinically important drug interactions: Drugs that increase effects/toxicity of zalcitabine: other potentially neurotoxic drugs including cisplatin, chloramphenicol, dapsone, disulfiram, ethionamide, glutethimide, gold, hydralazone, iodoquinol, isoniazid, metronidazole, nitrofurantoin, ribavirin, phenytoin, vincristine, alcohol, azathioprine, pentamidine, tetracyclines, thiazides, valproic acid, aminoglycosides, foscarnet. Parameters to monitor • Signs and symptoms of anemia: shortness of breath, dizziness, angina, pale conjunctiva, skin, and nailbeds. If peripheral neuropathy improves, zalcitabine may be readministered at 50% of the initial dose. The prescribing physician should be cognizant of these toxic effects and should advise the patient to discon- tinue the drug should they occur. Toxic effects include peripheral neuropathy (potentially reversible), pancreatitis (1. Food: Should be taken 30 minutes before or 1 hour after meal with a glass of water. Advice to patients • Take only prescribed dose and do not discontinue without consulting the treating physician. Clinically important drug interactions • Zidovudine increases effects/toxicity of dapsone, gancyclovir, vincristine, vinblastine, flucytosine, adriamycin, doxorubicin. If this occurs, it may be necessary to reduce the dosage or stop drug administration. Produces cranial vasoconstriction and decreased release of inflammatory neuropeptides. Editorial comments • Zolmitriptan, a new agent for acute treatment of migraine headaches, is very similar to sumatriptan. Adverse reactions • Common: headache, drowsiness, dizziness, diarrhea, drugged sensation, dry mouth. Editorial comments • Patient should be reevaluated if zolpidem is taken longer than 2–3 weeks. Controlled studies performed in pregnant women do not demonstrate a risk to the fetus during the first trimester of pregnancy with no evidence of risk in the second or third trimesters. Either studies in reproducing animals do not demonstrate a fetal risk but there are no controlled studies in pregnant women, or animal reproduction studies have shown adverse effects (other than a decrease in fertility) that were not confirmed in controlled studies in pregnant women in the first trimester and there is no evidence of a risk in later trimesters. Either study in animals has demonstrated adverse effects on the fetus (teratogenic, embryocidal, or other effects) and there are no controlled studies in women, or studies in women and animals are not available. These drugs should be given only if the potential benefits of the drug justify the potential or unknown risk to the fetus. There is positive evidence of human fetal risk, but the ben- efits from administration in pregnant women may be acceptable despite the risk. For example, if the drug is needed in a life-threatening situation or for a serious dis- ease for which safer drugs cannot be used or are ineffective, administration may be indicated. Animals or human studies have demonstrated fetal abnor- malities or there is evidence of risk to the fetus based on human experience, or both. The risk of the use of the drug in pregnant women clearly outweighs any possible bene- fit.
Some drugs cheap tadora online, such as cimetidine and erythromycin discount 20 mg tadora with visa, will decrease theophylline clearance and cause increased plasma theophylline concentrations (Table 14-1) purchase tadora from india. Suppository and rectal solution forms of the drug are available but are not commonly used. Intravenous infusion involves administration of theophylline itself or in a salt form (such as aminophylline). When theophylline derivatives are used, the theophylline dose equivalent should be calculated. Therefore, to obtain the theophylline dose equivalent, the aminophylline dose should be multiplied by 0. Others are designed to slowly release drug in the gastrointestinal tract for up to 24 hours after administration. Determine an appropriate loading dose of aminophylline to produce a theophylline concentration of 15 mcg/mL. In this case, the desired plasma theophylline concentration is 15 mcg/mL, the aminophylline salt equivalent (S) is 0. In patients more than 7 50% above ideal body weight, volume of distribution should be calculated using ideal body weight. The basic loading dose equation can be derived from the plasma concentration equation we learned in Lesson 1. This 650-mg aminophylline loading dose will produce a serum concentration slightly less than 15 mcg/mL. Note: Remember, aminophylline is a salt form of theophylline and contains approximately 80% theophylline equivalents. In this situation, we will slightly modify the loading dose Equation 14-2 to the following: (See Equation 14-2. This 450-mg aminophylline loading dose will result in a serum concentration slightly less than 15 mg/L. The loading dose is to be given over 30 minutes, and a maintenance infusion is to be started immediately. Suggest an aminophylline infusion rate to achieve a plasma theophylline concentration of 13 mcg/mL. Figure 14-1 demonstrates the relationship between serum levels achieved with the loading and maintenance doses of theophylline or aminophylline. A theophylline level is ordered immediately and is reported by the laboratory as 22 mcg/mL. Now that we have his actual clearance, we can calculate a new maintenance dose that will give us the desired theophylline serum concentration of 13 mcg/mL: (See Equation 14-4. Next we can determine the time we need to wait by using the following equation: -Kt C = C0e (See Equation 3-2. Clinical Correlate The most significant side effects from theophylline occur at serum concentrations higher than 20 mcg/mL. At concentrations higher than 35 mcg/mL, major adverse effects include hyperglycemia, hypotension, cardiac arrhythmias, seizures, brain damage, and death. Plasma concentrations with a loading dose and continuous infusion of theophylline or aminophylline. She has a history of heavy marijuana and tobacco use but no other medical problems. Suggest an oral dosage regimen that will produce a pss average of approximately 12 mcg/mL, using a sustained released product dosed every 12 hours. Department of Health and Human Services, Public Health Service, National Institutes of Health, National Heart, Lung, and Blood Institute; 1997. Recent advances in our understanding of the use of theophylline in the treatment of asthma. Theophylline: pooled Michaelis-Menten behavior of theophylline and its parameters (Vmax and Km) among asthmatic children and adults. Cimetidine inhibition of theophylline elimination: influence of adult age and time course. Phenytoin is usually administered either orally or intravenously and exhibits nonlinear or Michaelis-Menten kinetics (see Lesson 10). Unlike drugs undergoing first-order elimination (Figure 15-1), the plot of the natural logarithm of concentration versus time is nonlinear with phenytoin (Figure 15-2). Consequently, as the phenytoin dose increases, a disproportionately greater increase in plasma concentration is achieved. This enzyme saturation process can be characterized with an enzyme-substrate model first developed by the biochemists Michaelis and Menten in 1913. In this metabolic process, drug clearance is constantly changing (in a nonlinear fashion) as dose changes. To describe the relationship between concentration and dose, a differential equation can be written as shown below: (See Equation 10-1. Next, this differential equation can be expressed algebraically by assuming that we are at steady state and dX/dt is held constant. Then dX/dt, the change in the amount of drug (X) over time (t), can be expressed as X0/τ (dose over dosing interval), as shown in the following equation: (See Equation 10-1. The oral bioavailability of phenytoin is considered to be 100%, so an F factor is not needed in these calculations. Other pertinent clinical data include: weight, 75 kg; height, 5 feet, 11 inches; serum creatinine, 1. What intravenous loading dose and oral maintenance dose would you recommend to achieve and maintain a phenytoin concentration of approximately 20 mg/L? Calculation of the loading dose is not affected by the nonlinear pharmacokinetics of multiple-dose phenytoin regimens. Therefore: We could then order a dose of 1000 mg of phenytoin mixed in 100 mL of normal saline given intravenously via controlled infusion. The administration rate should not exceed 50 mg/minute to avoid potential cardiovascular toxicity associated with the propylene glycol diluent of the phenytoin injection. The accuracy of this loading dose estimate can be checked by obtaining a phenytoin plasma drug concentration at approximately 1 hour after the end of the loading dose infusion. Propylene glycol is a cardiotoxic agent and can cause various complications such as bradycardia and hypotension. This dose of 400 mg/day may be divided into 200 mg twice daily if necessary to decrease the likelihood of enzyme saturation and reduce concentration-dependent side effects. Therefore: Note how the units in the equation cancel out, yielding "mg/day" as the final units. It is difficult to calculate when multiple dosing with phenytoin will reach steady state because the time to steady state is concentration dependent. With drugs that undergo first-order elimination, steady state can be reached in three to five drug half-lives because this model assumes that clearance and volume of distribution are constant. However, because of its capacity-limited metabolism, phenytoin clearance decreases with increasing concentration. Therefore, the calculation of time to reach steady state is quite complicated and cannot be based on half-life. In fact, phenytoin does not have a true half-life; its half-life is dependent on drug concentration.
Various strategies to increase the solubility of a drug are given below; this subject is also discussed in detail in Chapter 6 (see Section 6 tadora 20mg online. Salt formation Formation of a corresponding water-soluble salt increases the dissolution rate in the gastrointestinal tract order tadora 20 mg on-line. This phenomenon can be explained by considering that a weakly acidic drug is unionized in the stomach and therefore has a low dissolution rate order cheap tadora line. If the free acid is converted to the corresponding sodium or potassium salt, the strongly alkali sodium or potassium cations exert a neutralizing effect. Thus in the immediate vicinity of the drug the pH is raised to, for example, pH 5–6, instead of pH of 1–2 in the bulk medium of the stomach, resulting in an alkaline microenvironment around the drug particle. This causes dissolution of the acidic drug in this localized region of higher pH, which gives rise to overall faster dissolution rates. When dissolved drug diffuses away from the drug surface into the bulk of the gastric fluid where the pH is again lower, the free acid form may precipitate out. However, the precipitated free acid will be in the form of very fine wetted drug particles. These drug particles exhibit a very large total effective surface area in contact with the gastric fluids, much larger than would have been obtained if the free acid form of the drug had been administered. Examples of the use of soluble salts to increase drug absorption include novobiocin, in which the bioavailability of the sodium salt of the drug is twice that of the calcium salt and 50 times that of the free acid. For example, the minor tranquilizer clorazepate is a prodrug of nordiazepam and is marketed as a dipotassium salt that is freely soluble in water, in contrast to the poorly soluble parent, norazepam. Polymorphic forms Many drugs can exist in more than one crystalline form, for example chloramphenicol palmitate, cortisone acetate, tetracyclines and sulphathiazole, depending on the conditions (temperature, solvent, time) under which crystallization occurs. This property is referred to as polymorphism and each crystalline form is known as a polymorph. At a given temperature and pressure only one of the crystalline forms is stable and the others are known as metastable forms. A metastable polymorph usually exhibits a greater aqueous solubility and dissolution rate, and thus greater absorption, than the stable polymorph. Amorphous forms The amorphous form of a drug has no crystalline lattice and therefore less energy is required for dissolution, so that the bioavailability of the amorphous form is generally greater than that of the crystalline form. For example, the amorphous form of novobiocin is at least 10 times more soluble than the crystalline form. Solvates Many drugs can associate with solvents to produce crystalline forms called solvates. Thus more rapid dissolution rates are often achieved with the anhydrous form of a drug. For example, the anhydrous forms of caffeine, theophylline and glutethimide dissolve more rapidly in water than do the hydrous forms of these drugs and the anhydrous form of ampicillin is about 25% more soluble in water at 37 °C than the trihydrate. Formulation factors The type of dosage form and its method of preparation or manufacture can influence drug dissolution and thus bioavailability. For example, there is no dissolution step necessary for a drug administered as a solution, while drugs in suspension are relatively rapidly absorbed because of the large available surface area of the dispersed solid. In solid dosage forms such as hard gelatin capsules or tablets, the processes of disintegration and deaggregation must occur before drug dissolution can proceed at any appreciable rate. Hence, the dissolution and thus bioavailability of a given drug generally tends to decrease in the following order of type of oral dosage form: aqueous solutions>aqueous suspensions>hard gelatin capsules> tablets. The effect of particle size on dissolution rate and bioavailability has been alluded to above and is discussed in detail in Section 6. These formulation additives may alter drug dissolution rates by such mechanisms as increasing the wetting of the dosage form, aiding rapid disintegration of the dosage form, forming poorly absorbable drug-excipient complexes and altering the pH. The effect of formulation factors on the dissolution rate for absorption routes other than the oral route is discussed in the relevant chapters. Drug degradation is generally a first order process and can be described by the following equation: (Equation 1. Solvolysis involves drug decomposition through a reaction with the solvent present, for example water, ethyl alcohol or polyethylene glycol. These solvents act as nucleophilic agents and attack electropositive centers of the drug molecule. Other degradation reactions include photolysis, racemization, and decarboxylation. The stability of the drug to degradative enzymes is of particular importance in vivo, as discussed above. Pharmacokinetics is the study of how drugs enter the body, reach the site of action and are removed from the body, i. Elimination is defined as the process of removal of the drug from the body, which may involve metabolism and/or excretion. The pharmacokinetic aspects of a drug are obviously just as important as its pharmacodynamics, when considering therapeutic efficacy. For many drugs this occurs by simple diffusion of the unionized form across cell membranes (see Section 1. When drugs are given by iv administration, there is an extremely high initial plasma concentration and the drug may rapidly enter and equilibrate with well-perfused tissues such as the lung, adrenals, kidneys, liver and heart. Subsequently, the drug enters poorly perfused tissues such as skeletal muscle, connective tissue and adipose tissue. As the concentration of drug in the poorly perfused tissues increases, there is a corresponding decrease in the concentration in the plasma and well-perfused tissues. Many drugs show an affinity for specific binding sites on plasma proteins such as albumin and α1-acid glycoprotein, which results in a reversible association, with some important consequences in therapeutics: • Drug binding lowers the concentration of free drug in solution, and thus the concentration of drug available to act at the receptor. This can result in the need to use high doses to compensate for drug wasteage, which is expensive. Unwanted deposition may also result in toxicity problems, arising from drug action at non-target sites. Classic examples of toxic side-effects resulting from unwanted drug distribution are found in cancer chemotherapy. The chemotherapeutic agent, a cytotoxic poison, lacks specificity and has the potential to kill all cells, both normal and malignant. The drug exploits the difference in the turnover of cancer cells, which is very much greater than normal cells. However, rapidly dividing normal cells, for example the hair follicles, and the cells of the gastrointestinal tract, are also susceptible to attack. This gives rise to typical side-effects associated with cancer chemotherapy such as hair loss and acute gastrointestinal disturbances. In the early 1900s Paul Ehrlich (who has been described as the father of drug delivery and therapeutics) pioneered the idea of the “magic bullet” approach, whereby therapy “could learn to aim”.