Abstract

To evaluate the safety of diltiazem in ordinary practice, post-marketing surveillance was performed using the prescription-event monitoring method.  The first 16,720 patients treated with diltiazem in general practice in the United Kingdom were identified from photocopies of prescriptions provided by the Prescription Pricing Authority.  After an interval of one year, event data were obtained from a questionnaire which was completed by the prescribing doctor.

The response rate was 67% and useful information was available for 10,119 patients.  The most important events which were likely to have been drug-related were heart block, bradycardia, skin rash and oedema.

Twenty-two reports of heart block were received (0.2%) all occurring during treatment with diltiazem.  There were no reports of heart block occurring post-treatment in the 3,921 patients who stopped diltiazem before the end of one year.  A beta-blocker was co-prescribed for 41% of patients with heart block, compared to 15% of the whole cohort; 0.6% of patients treated with a combination of diltiazem and a beta-blocker developed heart block.  All the cases of heart block were investigated further and eight patients with complete atrioventricular block were identified, three dying within 72 hours of its onset.  Ten patients had required treatment with a pacemaker.

Heart block is an uncommon but potentially serious complication of diltiazem treatment that is more likely to occur if the drug is used in combination with a beta-blocker.  Post-marketing surveillance of a large unselected cohort did not identify any important previously unrecognised adverse reactions to diltiazem.