Stability of alteplase for arms 1, 2, and 3. Alteplase concentrations are measured by RP-HPLC over 2, 4, and 6 hours. (A) When exposed to ultrasound alteplase degrades to approximately 90% of its original concentration in 2 hours. (B) When exposed to ultrasound alteplase degrades to approximately 80% of its original concentration in 4 hours. (C) When exposed to ultrasound alteplase degrades to approximately 70% of its original concentration in 6 hours.