Clopidogrel, like the homologous thienopyridine derivative tidopidine, selectively inhibits platelet aggregation induced by ADP. We have previously described two nucleotide-binding sites on platelets related to ADPmediated platelet responses. The first is a high-affinity binding she for 2-methylthio-ADP (2-MeSADP) that is linked to the inhibition of stimulated adenylate cyclase. The second is the 100-kd exofacial membrane protein aggregin, which is labeled by the reactive ADP analogue 5'-p-fluorosulfonyibenzoyl adenosine (FSBA) that is related to shape change and aggregation. We set out to determine if either of these sites is blocked in vivo by clopidogrel or its active metabolite. Six subjects were given clopidogrel (75 mg/day for 10 days) in a double-blind crossover experiment All of the subjects developed prolonged bleeding times while taking the drug. The rate of onset of the effect on bleeding time varied among subjects. Platelet aggregation induced by ADP or thrombin was significantly impaired by the drug treatment, but no effect was detected on shape change. The incorporation of [ 3 H]FSBA into aggregin was also unaffected. Inhibition of adenylate cyclase by ADP or by 2-MeSADP was greatly reduced in all subjects, and in the case of 2-MeSADP, there was evidence for a noncompetitive effect Inhibition of adenylate cyclase by epinephrine was unaffected. In the three subjects for whom binding measurements were made, the number of binding sites for [32 P]2-MeSADP was reduced from 534±44 molecules per platelet during control and placebo periods (11 determinations) to 199±78 molecules per platelet during drug treatment (three determinations). There was no consistent change in the binding affinity. The inhibition of platelet function by clopidogrel is associated with a selective reduction in the number of functional receptors mediating the inhibition of stimulated adenylate cyclase activity by ADP.

Chronicity and high therapeutic cost prompted this study to determine a cost-effective and efficacious regimen in treating narcotic-induced constipation. The efficacy of lactulose was compared with polyethylene glycol 3350/electrolyte solution for relief of methadone-induced constipation. This was a randomized, triple cross-over after control run-in (no treatment) study conducted at a methadone maintenance program in Baltimore, Maryland in 57 patients who are affected by opiate-induced constipation. The study was measured by self-reported frequencies, consistency, and ease of defecation during a 1 week run-in control period, followed by 3 treatment phases of 2 weeks each. Polyethylene glycol 3350/electrolyte solution and lactulose produced more "nonhard" stools than the placebo (P < 0.01) and control (P < 0.003). Polyethylene glycol 3350/electrolyte solution produced the loosest stool (P < 0.0001) compared with the control, whereas lactulose had the most adverse effects. There were no significant differences in reducing hard stool formation in either experimental group, but both were better than having nothing or just the placebo. Polyethylene glycol/electrolyte solution resulted in the loosest (diarrheal) stool. It is also likely that polyethylene glycol/electrolyte solution is the most cost effective.

Heparins are a heterogenous group of naturally occurring glycosaminoglycans characterized by anticoagulant activity and a wide range of molecular weights (low molecular weight or fractionated heparins evolving within the past two decades). Cofactors for endogenous inhibitors of coagulation (antithrombin III and heparin cofactor II), heparin administration results in a hypocoagulable state. Various platelet activities, including inhibition of activity induced by platelet-derived growth factors on vascular smooth muscle, also have been noted. Divorced of anticoagulant nature, novel applications may include a role in atherosclerosis prevention, acceleration of collateral coronary as well as peripheral circulation (i.e., angiogenesis), and continued (chronic) post-myocardial infarction therapy. Established indications include treatment of various thrombotic diseases, unstable angina, and thrombosis chemoprophylaxis in medical/surgical patients. The antithrombotic potential of the heparins is used also in thrombosis management related to extracorporeal circulatory assistance or dialysis devices. Heparin's therapeutic potential in the postphlebitic syndrome as well as in acute treatment of myocardial infarction (primarily and adjunctively with various thrombolytic agents) continues to undergo evaluation; however, early data review shows favorable trends for its inclusion in situations that favor thrombus generation (e.g., anterior myocardial infarction). Although associated with thrombocytopenia or hypertransaminasemia, the heparins are relatively well tolerated. In a small subset of patients, a severe thrombocytopenia may ensue, which generally resolves on medication withdrawal. As this class of glycosaminoglycans becomes better characterized, new indications may emerge for both native and the newer fractionated heparins.

Amiodarone is a unique antiarrhythmic agent originally developed as a vasodilator. Classified electrophysiologically as a Type III antiarrhythmic, it also has both nonspecific antisympathetic and direct, fast channel-membrane effects. Hemodynamic effects of orally administered amiodarone (a negative inotropic agent) are usually negligible, and are usually compensated for by induced vasodilation. Effects on thyroid and hepatic function may help to explain some of the unique pharmacologic as well as toxicologic effects of the drug. Amiodarone is poorly bioavailable (20-80%) and undergoes extensive enterohepatic circulation before entry into a central compartment. The principal metabolite, mono-n-desethyl amiodarone is also an antiarrhythmic. From this central compartment, it undergoes extensive tissue distribution (exceptionally high tissue/plasma partition coefficients). The distribution half-life of amiodarone out of the central compartment to peripheral and deep tissue compartments (t1/2 alpha) may be as short as 4 hours. The terminal half-life (t1/2 beta) is both long and variable (9-77 days) secondary to the slow mobilization of the lipophilic medication out of (primarily) adipocytes. A pharmacokinetically based loading scheme is described, and data suggesting a role for routine amiodarone plasma levels are presented.

Discovered early in this century consequent to investigations of a bovine hemorrhagic disease, the oral anticoagulants inhibit a post translational modification required for various hepatically derived serine proteases to become active. These include Factors II, V, VII and X. Through their effect on Proteins S and C, the extrinsic pathway is also effected. While most of these agents exist as optically active enantiomers, with differing kinetics and pharmacologic profiles, they are generally administered in the clinic as racemic mixtures. Over the last 45 years, various studies have sought to better evaluate the role of the oral anticoagulation in both prevention and treatment of various types of thrombo-occlusive and -embolic disease. Such exercises have allowed us to better understand the pathophysiology of those diseases as well as to better characterize the pre-thrombotic state.