Recombinant hirudin (HBW 023) produces stable anticoagulation unaffected by circadian variation in patients with thrombolysis for acute myocardial infarction.

Background: Circadian variations have been described for a number of haemostatic and physiological factors, all of which might predispose towards clotting in the late morning. The anticoagulation effect of heparin has been shown to respond in a circadian manner, resulting in minimal prolongation of the activated partial thromboplastin time (aPTT) in the morning.

Methods: Recombinant hirudin (HBW 023) given as a bolus of 0.07, 0.1, 0.2 or 0.4 mg.kg-1 followed by an infusion of 0.05, 0.06, 0.1 or 0.15 mg.kg-1 over 48 h was used as conjunctive therapy to thrombolysis with front-loaded recombinant tissue-type plasminogen activator (100 mg.90 min-1) in 40 patients with acute myocardial infarction. APTT, activated clotting time and free hirudin plasma levels were determined at baseline and at 8, 12, 16, 20, 24, 32, 40 and 48 h.

Results: The prolongation of aPTT and activated clotting time was dose-dependent and stable. In 82.5% of the patients, aPTT values were ranged between the highest and the lowest aPTT of < 30 s. When the results were divided into four time intervals (0000-0600, 0600-1200, 1200-1800, 1800-2400) neither in the individual patients nor in the mean values of the four different dose groups was any significant circadian variation in aPTT or activated clotting time prolongation observed. The pharmacokinetic studies of free hirudin plasma levels revealed no circadian rhythm either. All but one patient (97.5%) had a patent vessel (TIMI grade 2/3) at the end of the hirudin infusion.

Conclusions: Recombinant hirudin, in contrast to heparin, does not show any circadian variation in its anticoagulation effect. This might, in part, explain the more stable and predictable anticoagulation achieved by hirudin, which is associated with a reduced rate of reocclusions after thrombolysis.