An open-label drug substitution study showed that controlled-release isradipine (Dynacirc-CR) can be safely substituted for amlodipine on a mg-for-mg basis in patients with mild-to-moderate hypertension. When controlled-release isradipine was substituted for amlodipine, blood pressure was more effectively controlled, and edema rates were reduced. When subjects resumed amlodipine therapy, the previous gain in blood pressure reduction and lessening of edema vanished. The basis for this more favorable pattern of efficacy and side-effects with controlled-release isradipine, although mechanistically unresolved, may relate to a lesser degree of sympathetic nervous system activation.