Urokinase Therapy: Dosage Schedules and Coagulant Side Effects

S ummary The effect of a new preparation of urokinase (Roche) has been studied, in the laboratory and in 10 patients and three volunteers. It is a non‐toxic and active fibrinolytic agent if given in adequate dosage, but it was found that a small initial infusion gave rise to a paradoxical coagulant effect in the recipient. This effect was associated with the formation of‘cryofibrinogen’ and an increase in factor‐VIII activity. The coagulant effect was probably mediated by a low‐grade process of plasminogen activation rather than due to the preparation of urokinase itself. The preparation did have minor intrinsic thromboplastic activity similar to that described in other preparations of urokinase, but it is unlikely that this would produce a significant effect in vivo . The coagulant effect could be overcome by increasing the initial dose of urokinase to produce rapidly the haemostatic defect normally associated with fibrinolytic therapy.