Abrupt Withdrawal of Isosorbide 5-Mononitrate (Imdur®) after Long Term Treatment in Stable Angina Pectoris

32 patients with stable angina pectoris who had been receiving a controlled-release formulation Durules® of isosorbide 5-mononitrate (Imdur®) 60 to 120mg daily with concomitant β-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 Isosorbide 5-mononitrate was abruptly withdrawn and substituted with placebo for 2 weeks, after which the active drug was reintroduced.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.