The detection of antibody formation is highly dependent upon the sensitivity and specificity of the assay. The absolute immunogenicity rates reported here are difficult to compare with the results from other products due to differences in assay methodology, patient populations, and other underlying factors.

The potential for development of antibodies to RECOTHROM Thrombin topical (Recombinant) was evaluated in multiple clinical trials and included patients with a single exposure to RECOTHROM as well as patients who were re-exposed to RECOTHROM during a subsequent surgical procedure. Only patients with both baseline and post-treatment antibody specimens available were evaluated for the development of specific anti-RECOTHROM product antibodies, which was defined as seroconversion or a ≥1.0 titer unit (≥10-fold) increase in antibody levels after study treatment. Five of 609 (0.8%; 95% CI, 0.4%-2.8%) evaluable patients developed specific anti-RECOTHROM product antibodies. None of these antibodies were found to neutralize native human thrombin. There was no difference in anti-RECOTHROM product antibody formation incidence among patients exposed to RECOTHROM applied with absorbable gelatin sponge, USP or with spray applicator.

In a clinical trial comparing RECOTHROM to bovine thrombin (N=411; n=398 antibody evaluable) for the development of specific anti-product antibodies, blood samples were collected at baseline and at Day 29 in both treatment groups and were analyzed by ELISA.1 At baseline, 1.5% of RECOTHROM patients (n=3/198) had positive anti-product antibody titers compared with 5% of bovine thrombin patients (n=10/200). Of these patients, none of the RECOTHROM group and eight in the bovine thrombin group exhibited ≥1.0 titer unit (≥10-fold) increases in anti-product antibody levels after study treatment. 

At Day 29, three of 198 (1.5%; 95% CI, 0%-4%) patients in the RECOTHROM group developed specific anti-product antibodies (one patient also developed anti-CHO host cell protein antibodies); 43 of 200 patients in the bovine thrombin group (22%; 95% CI, 16%-28%) developed specific antibodies to bovine thrombin product. Treatment with RECOTHROM resulted in a statistically significant lower incidence of specific anti-product antibody development. Because the study was not powered to detect a difference in clinical outcomes attributable to antibody formation, no conclusions can be drawn regarding the clinical significance of the difference in antibody formation based on the results of this study. None of the antibodies in the RECOTHROM group neutralized native human thrombin. Antibodies against bovine thrombin product were not tested for neutralization of native human thrombin.

In a trial of patients with a high likelihood of prior exposure to bovine thrombin, 15.6% of patients (n=32/205) had anti-bovine thrombin product antibodies and 2% of patients (n=4/200) had anti-RECOTHROM product antibodies at baseline.2 Following treatment, none of the 200 evaluable patients (patients for whom post-treatment specimens were available) developed antibodies to RECOTHROM.

In a trial of patients previously exposed to RECOTHROM, 31 patients were re-exposed to  
RECOTHROM during a subsequent surgery.3 None of the evaluable patients (n=30) had anti-  
RECOTHROM product antibodies at baseline and none developed antibodies at Day 29.

In a trial of RECOTHROM, including 26 pediatric patients (aged one month to 16 years) and four patients 17 years of age, one patient without prior thrombin exposure had pre-existing anti-RECOTHROM product antibodies at baseline.5 None of the 27 evaluable patients developed anti-RECOTHROM product antibodies at Day 29.