Initial experience with a direct antithrombin, Hirulog, in unstable angina. Anticoagulant, antithrombotic, and clinical effects.

BACKGROUND

Currently available antithrombotic therapy for unstable angina is unwieldy and occasionally ineffective. This study was designed to investigate the potential of Hirulog, a new synthetic specific antithrombin agent, for the management of this condition.

METHODS AND RESULTS

A total of 55 patients in the acute phase of unstable angina received intravenous Hirulog according to one of two protocols. In an acute dose-escalating study, 0.02, 0.05, 0.1, 0.25, and 0.5 mg.kg-1 x h-1, each for 30 minutes, were infused in 15 patients. Prolongation of activated partial thromboplastin time (aPTT) (r = .95), fibrinopeptide A inhibition (r = .96), and Hirulog plasma levels (r = .91) correlated closely with the dose infused, with significant changes compared with baseline appearing at doses of 0.25 mg.kg-1 x h-1 and higher. The purposes of the second protocol were to determine whether the anticoagulant and antithrombotic effects of the drug were sustained during a 72-hour infusion and to assess whether such treatment prevented the complications of unstable angina. Based on the initial study, we planned to give a dose of 0.25 mg.kg-1 x h-1 to each patient until 2 patients failed therapy, then successively higher doses until a 95% success rate was achieved or adverse effects intervened, increasing the dose after two failures had occurred at each level. Five patients received the 0.25-mg.kg-1 x h-1 dose and 14 the 0.5-mg.kg-1 x h-1 dose before two failures occurred. Failure was observed in only one of 21 patients at the dose of 1 mg.kg-1 x h-1. aPTT (+/- SEM) levels increased to 62 +/- 5, 76 +/- 2, and 98 +/- 3 seconds at the three doses, with minimal intraindividual variation, and Hirulog plasma levels to 1050, 2100, and 4200 mg/mL, respectively. Fibrinopeptide A plasma levels decreased at all doses but more consistently at the dose of 1 mg.kg-1 x h-1. The overall clinical success rate was 87.5%: 60% (3/5) at the low dose, 86% (12/14) at the intermediate dose, and 95% (20/21) at the high dose. No deaths, myocardial infarctions, or bleeding complications occurred.

CONCLUSIONS

In unstable angina patients, Hirulog infusions quickly and reproducibly yield stable, dose-dependent anticoagulant and antithrombotic effects with a favorable clinical efficacy profile.