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Introduction: The antiplatelet agents ticlopidine and clopidogrel are thienopyridine derivatives that are commonly used for secondary prevention of cerebrovascular events, prevention of coronary artery stent thrombosis, and for treatment of acute coronary syndrome. While these chemically related agents are the first and third most common causes of drug-associated TTP respectively, clinical presentations, laboratory findings, and outcomes suggest that there may be two distinct mechanistic pathways. Methods: Clinical and laboratory data for 60 cases of ticlopidine-associated TTP and 35 cases of clopidogrel associated TTP were reviewed. Results: Type 1 thienopyridine-associated TTP, characterized by onset of disease > 5 days after drug initiation, occurred in 98% of the ticlopidine patients versus 63% of the clopidogrel patients. Laboratory studies identified severe deficiency of ADAMTS13 activity and the presence of IgG inhibitors in 7 ticlopidine (Tsai, et al.; Annals of Internal Medicine, 2000) and 2 clopidogrel (Bennett, et al.; NEJM, 2000) patients. Survival was 68% in the ticlopidine patients versus 91% in the clopidogrel patients. Type 2 thienopyridine-associated TTP, consisting of TTP onset within 5 days of drug initiation, occurred in 2% of the ticlopidine patients versus 37% of the clopidogrel patients. Laboratory studies failed to identify deficient ADAMTS13 activity or the presence of IgG inhibitors in 1 clopidogrel patient (Zheng, et al.; Blood, 2004). Survival was 0% in the ticlopidine patients versus 38% in the clopidogrel patients. Conclusion: The proposed type 1 and type 2 thienopyridine-associated TTP may be distinguished on the basis of clinical presentation, ADAMTS13 levels, and outcome. Type 1 thienopyridine-associated TTP—characterized as occurring after > 5 days of thienopyridine treatment, severely deficient ADAMTS13 activity and presence of IgG inhibitors, and high survival rates with plasmapheresis—is more likely to occur in patients receiving ticlopidine. Type 2 thienopyridine-associated TTP—characterized as occurring within 5 days of thienopyridine therapy initiation, normal ADAMTS13 activity and undetectable IgG inhibitors, and poor survival rates despite plasmapheresis—is more likely to occur in patients receiving clopidogrel. Additional confirmatory studies on larger numbers of patients are needed.

The pharmacodynamic effects of single oral doses of atenolol (100 mg), labetalol (300 mg), and propranolol (80 mg) were compared with those of placebo in a randomized, double-blind, Latin square design in 12 patients with hypertension. Atenolol and propranolol both significantly reduced cardiac output (-0.55 vs. -0.31 L/min) and heart rate (-8.0 vs. -6.6 bpm), whereas labetalol had no effect on either parameter (-0.08 L/min; + 1.0 bpm). Labetalol significantly reduced vascular resistance (-339 dynes X cm/sec5), but atenolol and propranolol did not (147 vs. 62 dynes X cm/sec5). Only labetalol significantly reduced the systolic (-15.3 mm Hg), diastolic (-11.5 mm Hg), and mean blood pressures (-12.8 mm Hg). Atenolol significantly reduced only diastolic blood pressure (-5.20 mm Hg), whereas propranolol failed to lower these parameters significantly. These data indicate that the hemodynamic profile of labetalol differs from that of selective and nonselective beta-blockers. Labetalol lowered blood pressure primarily by reducing vascular resistance, whereas reductions in heart rate and cardiac output were the predominant effects of atenolol and propranolol.

We examined in normal men and women the effects of chronic ethanol consumption and the coadministration of cimetidine and ranitidine on the kinetics of ethanol. We found that the consumption of 45 gm ethanol per day for 3 weeks increased the apparent volume of distribution of ethanol in men from 732 to 884 ml/kg (P < 0.01) but had no such effect in women (697 ml/kg before ethanol and 746 ml/kg after chronic ethanol consumption). This combined therapy had no effect on the rate of ethanol disappearance in either sex. In men the rate of disappearance was 165 mg/L/hr before and 168 mg/L/hr after chronic consumption, while in women the respective values were 209 and 203 mg/L/hr. The addition of either cimetidine or ranitidine had no effect on either parameter compared with values observed on day 22 of the study. In view of the known inhibitory effects of cimetidine on cytochrome P-450–dependent enzymes, our data suggest that this enzyme system does not metabolize a significant fraction of ingested ethanol in subjects who have consumed moderate doses of alcohol for several weeks. Clinical Pharmacology and Therapeutics (1985) 38, 157–163; doi:10.1038/clpt.1985.152

Flecainide and verapamil are antiarrhythmic agents that may be used in combination. We have examined their pharmacodynamic interaction by M-mode echocardiography and electrocardiography in eight normal male volunteers (24 +/- 1.8 years of age). Flecainide decreased the left ventricular ejection fraction (LVEF) (-4.4 +/- 1.2%, p less than 0.008), but verapamil did not. Neither drug affected cardiac output or vascular resistance. Both drugs increased the PR interval (12 +/- 4 msec, p less than 0.01 for flecainide; 12 +/- 5, p less than 0.04 for verapamil). Flecainide, but not verapamil, increased the QTc interval (23 +/- 8 msec, p less than 0.02). Both drugs also increased the systolic time interval ratio (PEPc/LVETc) (0.074 +/- 0.012, p less than 0.0004 for flecainide; 0.029 +/- 0.008, p less than 0.007 for verapamil). The combination of flecainide and verapamil had additive effects on myocardial contractility and on atrioventricular conduction. Verapamil slightly decreased the plasma clearance of flecainide (7.78 +/- 0.60 ml/kg/min for flecainide alone, 7.34 +/- 0.48 ml/kg/min for flecainide and verapamil together, p less than 0.05). On the other hand, flecainide had no effect on the plasma clearance of verapamil, which suggests that there was little interaction between the two drugs on their pharmacokinetic parameters.