Safety and Efficacy of Therapeutically Equivalent Doses of Sustained‐Release Formulations of Isradipine and Felodipine

This open-label, drug substitution study was conducted to determine if subjects receiving sustained-release isradipine (SR-I) can be safely switched to sustained-release felodipine (SR-F) and to assess whether SR-I provides better 24-hour blood pressure (BP) control than SR-F. Forty-one men receiving either SR-F 5 mg or SR-F 10 mg once daily for at least 6 months were switched to an equivalent dose of SR-I; BP was measured 2, 4, and 6 weeks after substitution. Significant reductions in systolic BP were seen in the SR-I 10 mg group after 4 weeks and they remained significantly lower through 6 weeks (p< or =0.05). Diastolic BP was reduced, but not significantly. After 6 weeks, SR-F therapy was reinstated, and BP returned toward baseline values. No serious adverse events were reported. SR-I can be safely substituted for SR-F and may provide better 24-hour control of BP than SR-F.