STREPTOKINASE NEUTRALIZATION TITERS UP TO 866 DAYS AFTER INTRAVENOUS STREPTOKINASE FOR ACUTE MYOCARDIAL-INFARCTION

Objective-To follow the change in streptokinase neutralisation titres in a group of patients after treatment with streptokinase for acute my ocardial infarction. Design-Venous blood samples suitable for analysis were obtained up to 866 days after treatment with 1.5 million units o streptokinase in 189 patients. The ability of the patient's plasma to inhibit lysis o a thrombin clot by streptokinase was assessed. Settin g-A coronary care unit in a district general hospital. Patients-A retr ospective review of coronary care records and the district health auth ority computer showed that 329 patients who had received streptokinase were alive. All were invited for venepuncture and 220 (67%) attended. Satisfactory samples were obtained from 189 patients. Results-Raised titres of antibody sufficient to neutralise a standard dose of 1.5 mil lion units of streptokinase were found in 90% of patients. There was a fall in streptokinase neutralisation titre with increasing time after administration of streptokinase (r = -0.35, P < 0.0001) and though th ere was considerable variation among the group the neutralisation titr e was higher than in the general population in all patients, even thos e who had received streptokinase at least two years previously. Conclu sion-The ability of streptokinase to lyse a thrombin clot was apprecia bly inhibited in vitro by the plasma from patients who had received 1. 5 million units of streptokinase. High streptokinase neutralisation ti tres persisted for a long time after the use of streptokinase as throm bolytic treatment for acute myocardial infarction. Readministration of streptokinase may not be efficacious for considerably longer than the one year currently advocated. Until the in vivo effects of streptokin ase readministration are known a non-antigenic thrombolytic agent shou ld be used instead.