Urokinase activity after freezing: Implications for thrombolysis in intraventricular hemorrhage

The retention of urokinase activity after frozen storage was studied. Urokinase powder was reconstituted aseptically in sterile water for injection or preservative-free 0.9% sodium chloride injection to a final concentration of 5000 IU/mL. Samples were stored in 5mL. plastic syringes at -20 or -70 degrees C for up to six months. Samples containing urokinase 25,000 IU/mL were similarly prepared by using sodium chloride injection as the diluent and were stored frozen at the same temperatures for up to 93 days. Urokinase activity was measured with a chromogenic assay at each test interval. Samples were also cultured after thawing to evaluate their potential to support microbial growth. The activity of urokinase at either concentration did not change appreciably during the study period. The method of thawing-at room temperature or in a refrigerator-had no effect on urokinase activity. No microbial growth was observed. Urokinase 5000 IU/mL did not show any changes in activity when reconstituted with sterile water for injection or 0.9% sodium chloride injection and frozen for up to six months. Urokinase 25,000 IU/mL in sodium chloride injection was also stable after 93 days of frozen storage.