Abrupt withdrawal of isosorbide 5-mononitrate (Imdur) after long term treatment in stable angina pectoris. A preliminary report.

32 patients with stable angina pectoris who had been receiving a controlled-release formulation Durules of isosorbide 5-mononitrate (Imdur) 60 to 120 mg daily with concomitant beta-blocker therapy for at least 1 year were entered into a study to evaluate possible rebound phenomena from the abrupt withdrawal of isosorbide 5-mononitrate and to determine whether nitrate tolerance had developed. Isosorbide 5-mononitrate was abruptly withdrawn and substituted with placebo for 2 weeks, after which the active drug was reintroduced. No deterioration of exercise performance could be detected during withdrawal of therapy, but an increase was seen after reinstitution. No tolerance was found for systolic blood pressure and ST segment changes or for the number of anginal attacks and short-acting glyceryl trinitrate tablets consumed. Three patients had to be hospitalised because of a sudden deterioration of symptoms on withdrawal of isosorbide 5-mononitrate. It was concluded that isosorbide 5-mononitrate in Durules has a beneficial effect and that tolerance does not appear to be clinically relevant.