Items in AFP with MESH term: Drug Interactions
ABSTRACT: The Seventh American College of Chest Physicians (ACCP) Conference on Antithrombotic and Thrombolytic Therapy provides guidelines for outpatient management of anticoagulation therapy. The ACCP guidelines recommend short-term warfarin therapy, with the goal of maintaining an International Normalized Ratio (INR) of 2.5 +/- 0.5, after major orthopedic surgery. Therapy for venous thromboembolism includes an INR of 2.5 +/- 0.5, with the length of therapy determined by associated conditions. For patients with atrial fibrillation, the INR is maintained at 2.5 +/- 0.5 indefinitely; for most patients with mechanical valves, the recommended INR is 3.0 +/- 0.5 indefinitely. Use of outpatient low-molecular-weight heparin (LMWH) is as safe and effective as inpatient unfractionated heparin for treatment of venous thromboembolism. The ACCP recommends starting warfarin with unfractionated heparin or LMWH for at least five days and continuing until a therapeutic INR is achieved. Because patients with venous thromboembolism and cancer who have been treated with LMWH have a survival advantage that extends beyond their venous thromboembolism treatment, the ACCP recommends beginning their therapy with three to six months of LMWH. When invasive procedures require the interruption of oral anticoagulation therapy, recommendations for bridge therapy are determined by balancing the risk of bleeding against the risk of thromboembolism. Patients at higher risk of thromboembolization should stop warfarin therapy four to five days before surgery and start LMWH or unfractionated heparin two to three days before surgery.
ABSTRACT: Chronic kidney disease affects renal drug elimination and other pharmacokinetic processes involved in drug disposition (e.g., absorption, drug distribution, nonrenal clearance [metabolism]). Drug dosing errors are common in patients with renal impairment and can cause adverse effects and poor outcomes. Dosages of drugs cleared renally should be adjusted according to creatinine clearance or glomerular filtration rate and should be calculated using online or electronic calculators. Recommended methods for maintenance dosing adjustments are dose reductions, lengthening the dosing interval, or both. Physicians should be familiar with commonly used medications that require dosage adjustments. Resources are available to assist in dosing decisions for patients with chronic kidney disease.
ABSTRACT: Cytochrome P450 enzymes are essential for the metabolism of many medications. Although this class has more than 50 enzymes, six of them metabolize 90 percent of drugs, with the two most significant enzymes being CYP3A4 and CYP2D6. Genetic variability (polymorphism) in these enzymes may influence a patient's response to commonly prescribed drug classes, including beta blockers and antidepressants. Cytochrome P450 enzymes can be inhibited or induced by drugs, resulting in clinically significant drug-drug interactions that can cause unanticipated adverse reactions or therapeutic failures. Interactions with warfarin, antidepressants, antiepileptic drugs, and statins often involve the cytochrome P450 enzymes. Knowledge of the most important drugs metabolized by cytochrome P450 enzymes, as well as the most potent inhibiting and inducing drugs, can help minimize the possibility of adverse drug reactions and interactions. Although genotype tests can determine if a patient has a specific enzyme polymorphism, it has not been determined if routine use of these tests will improve outcomes.
Genetic Factors In Drug Metabolism - Article
ABSTRACT: Patients vary widely in their response to drugs. Having an understanding of the pharmacokinetic and pharmacodynamic properties of various medications is importantwhen assessing ethnic differences in drug response. Genetic factors can account for 20 to 95 percent of patient variability. Genetic polymorphisms for many drug-metabolizing enzymes and drug targets (e.g., receptors) have been identified. Although currently limited to a few pathways, pharmacogenetic testing may enable physicians to understand why patients react differently to various drugs and to make better decisions about therapy. Ultimately, this understanding may shift the medical paradigm to highly individualized therapeutic regimens.
ABSTRACT: Family physicians commonly care for patients with serious mental illness. Patients with psychotic and bipolar disorders have more comorbid medical conditions and higher mortality rates than patients without serious mental illness. Many medications prescribed for serious mental illness have significant metabolic and cardiovascular adverse effects. Patients treated with second-generation antipsychotics should receive preventive counseling and treatment for obesity, hyperglycemia, diabetes, and hyperlipidemia. First- and second-generation antipsychotics have been associated with QT prolongation. Many common medications can interact with antipsychotics, increasing the risk of cardiac arrhythmias and sudden death. Drug interactions can also lead to increased adverse effects, increased or decreased drug levels, toxicity, or treatment failure. Physicians should carefully consider the risks and benefits of second-generation antipsychotic medications, and patient care should be coordinated between primary care physicians and mental health professionals to prevent serious adverse effects.
ABSTRACT: Pneumonia is an important cause of morbidity and mortality in nursing home residents, with 30-day mortality rates ranging from 10 to 30 percent. Streptococcus pneumoniae is the most common cause of nursing home-acquired pneumonia, although Staphylococcus aureus and gram-negative organisms may be more common in severe cases. Antibiotic therapy for nursing home-acquired pneumonia should target a broad range of organisms, and drug-resistant microbes should be considered when making treatment decisions. In the nursing home setting, treatment should consist of an antipneumococcal fluoroquinolone alone or either a high-dose beta-lactam/beta-lactamase inhibitor or a second- or third-generation cephalosporin, in combination with azithromycin. Treatment of hospitalized patients with nursing home-acquired pneumonia requires broad-spectrum antibiotics with coverage of many gram-negative and gram-positive organisms, including methicillin-resistant S. aureus. Appropriate dosing of antibiotics for nursing home-acquired pneumonia is important to optimize effectiveness and avoid adverse effects. Because many nursing home residents take multiple medications, it is important to consider possible drug interactions.
ABSTRACT: While the choices available for the management of gram-positive, drug-resistant bacterial infections are becoming limited, antimicrobial resistance is becoming increasingly problematic because of the widespread overuse of antibiotics. Linezolid is a synthetic antibiotic belonging to a new class of antimicrobials called the oxazolidinones. Linezolid disrupts bacterial growth by inhibiting the initiation process of protein synthesis—a mechanism of action that is unique to this class of drugs. It is well absorbed with high bioavailability that allows conversion to oral therapy as soon as the patient is clinically stable. It has been approved for certain gram-positive infections including certain drug-resistant enterococcus, staphylococcus, and pneumococcus strains. It is generally well tolerated, with myelosuppression being the most serious adverse effect. As a nonselective inhibitor of monoamine oxidase, caution is recommended when used with adrenergic or serotonergic agents (e.g., tyramine, dopamine, pseudoephedrine, and selective serotonin reuptake inhibitors). Judicious use of this medication should help physicians treat patients with multidrug-resistant infections.
Newsletter - AAFP News: AFP Edition
ABSTRACT: Diabetic peripheral neuropathic pain affects the functionality, mood, and sleep patterns of approximately 10 to 20 percent of patients with diabetes mellitus. Treatment goals include restoring function and improving pain control. Patients can realistically expect a 30 to 50 percent reduction in discomfort with improved functionality. The main classes of agents used to treat diabetic peripheral neuropathic pain include tricyclic antidepressants, anticonvulsants, serotonin-norepinephrine reuptake inhibitors, opiates and opiate-like substances, and topical medications. Physicians should ask patients whether they have tried complementary and alternative medicine therapies for their pain. Only two medications are approved specifically for the treatment of diabetic peripheral neuropathic pain: pregabalin and duloxetine. However, evidence supports the use of other therapies, and unless there are contraindications, tricyclic antidepressants are the first-line treatment. Because patients often have multiple comorbidities, physicians must consider potential adverse effects and possible drug interactions before prescribing a medication.
ABSTRACT: Many drug interactions are a result of inhibition or induction of cytochrome P450 enzymes (CYP450). The CYP3A subfamily is involved in many clinically significant drug interactions, including those involving nonsedating antihistamines and cisapride, that may result in cardiac dysrhythmias. CYP3A4 and CYP1A2 enzymes are involved in drug interactions involving theophylline. CYP2D6 is responsible for the metabolism of many psychotherapeutic agents. The protease inhibitors, which are used to treat patients infected with the human immunodeficiency virus, are metabolized by the CYP450 enzymes and consequently interact with a multitude of other medications. By understanding the unique functions and characteristics of these enzymes, physicians may better anticipate and manage drug interactions and may predict or explain an individual's response to a particular therapeutic regimen.