Post-marketing surveillance of the safety of cimetidine: twelve-month morbidity report.
A total of 9928 patients taking cimetidine and 9351 controls were included in a post-marketing drug surveillance study in Glasgow, Nottingham, Oxford and Portsmouth; 98.8 per cent of the takers and 97.7 per cent of the controls were successfully followed up for at least one year during which hospital visits and deaths were recorded. Methods of identification of subjects and 12-month mortality results have been reported previously. A general analysis of the morbidity experienced by these patients during the study year is presented here. Thirty-nine per cent of takers and 21 per cent of controls were seen at outpatient clinics, and 18 per cent of takers and 8 per cent of controls were admitted to hospital; 15 325 individual diagnoses in takers and 5002 diagnoses in controls were reviewed. An association with cimetidine treatment was found, as expected, for gastrointestinal diseases. Weaker associations were found for haematological disorders, some tumours, infections, disorders of the locomotor system and respiratory diseases. Detailed examination revealed that these were mainly due to confounding from several sources, for example, from the underlying cause of the dyspepsia which resulted in cimetidine use, from the higher level of physician contact in cimetidine takers, and smoking. The scheme successfully detected and quantified some already known adverse effects of cimetidine and did not detect any new effects. It is concluded that this method of collecting information is feasible and useful, but several interpretive pitfalls arise, some of which can be avoided by careful analysis. No evidence of any major unrecognised risk of cimetidine treatment emerged from the study.