Compliance as a Factor in the Development of Nitrate Tolerance: A Patient Investigation

Telephone interviews were conducted to establish the prescribing instructions given by experienced physicians to patients with angina pectoris treated with long-acting nitrates. In addition, the times of day when doses were taken were recorded. The aim of the study was to determine whether or not an asymmetric dosing regimen was being followed by the patients. The majority (62.7%) of patients were being treated with 5-isosorbide mononitrate taken orally twice daily. All but two took the correct number of tablets, but more than 50% of these patients were not taking the second tablet at the correct time to achieve the recommended 6 − 8-h period during which the plasma nitrate concentration was sufficiently low to avoid nitrate tolerance. Possible explanations for the incorrect use of the prescribed drug may be that the patients did not understand the physician's instructions and did not appreciate the importance of rigidly adhering to these instructions. A more satisfactory approach, with improved patient compliance, may be a once-daily dosing regimen.