STUDY OBJECTIVE:To evaluate the safety and immunogenicity of recombinant human thrombin (rThrombin), an active topical stand-alone hemostatic agent. DESIGN:Analysis of pooled data from 10 rThrombin clinical trials. PATIENTS:A total of 644 adult and pediatric patients treated with rThrombin; 609 patients were included in the immunogenicity analysis. MEASUREMENTS AND MAIN RESULTS:In all studies, rThrombin was applied during a single surgical procedure (day 1); the procedures consisted of spinal procedures, major hepatic resection, peripheral arterial bypass, arteriovenous graft formation for hemodialysis access, and synchronous burn wound excision and skin grafting. A dosage of 1000 IU/ml of rThrombin was administered for more than 99% of patients. Adverse events and clinical laboratory values were monitored through day 29. Blood samples were obtained for immunogenicity analyses before the procedure and on day 29. Adverse events were mild or moderate in severity for the majority of patients; no patients discontinued from an rThrombin study due to adverse events. The most commonly reported adverse events in the 644 patients were incision site pain (305 patients [47.4%]), procedural pain (215 patients [33.4%]), and nausea (170 patients [26.4%]). Five patients (0.8%) died during the studies; all deaths were considered unrelated to rThrombin treatment. Antibodies to the rThrombin product developed in 5 (0.8%, 95% confidence interval 0.4-2.8%) of 609 patients by day 29, approximately 1 month after treatment; these antibodies did not neutralize the activity of native human thrombin. The development of antibodies did not appear to differ substantively by type of surgical procedure, amount of rThrombin administered, or patient age. CONCLUSION:Recombinant human thrombin was well tolerated, and adverse events were consistent with those reported in the postoperative setting in the surgical populations studied. Approximately 1 month after treatment, less than 1% of the patients had developed antibodies to the rThrombin product, and these antibodies did not neutralize the activity of native human thrombin. These results support the safety of rThrombin when used as a topical aid to hemostasis in numerous surgical settings and for patients of differing ages.