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 injecti on or preservative-free 0.9% sodium chloride injection to a final concentra tion 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 diluen t and were stored frozen at the same temperatures for up to 93 days. Urokin ase activity was measured with a chromogenic assay at each test interval. S amples were also cultured after thawing to evaluate their potential to supp ort microbial growth. The activity of urokinase at either concentration did not change appreciabl y 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 reconstitute d with sterile water for injection or 0.9% sodium chloride injection and fr ozen for up to six months. Urokinase 25,000 IU/mL in sodium chloride inject ion was also stable after 93 days of frozen storage.