Differences in perceived and presented adverse drug reactions in general practice.

Background: Postmarketing surveillance (PMS) studies are frequently based on data from general practitioners (GPs). Patients, however, do not always report to their GP suspected adverse drug reactions.

Setting: A postmarketing cohort study on adverse reactions to sumatriptan, performed with assistance of drug dispensing GPs in The Netherlands.

Methods: Questionnaires were sent to all drug-dispensing GPs in The Netherlands, as well as to their patients on sumatriptan. To avoid bias, no specific adverse reactions were mentioned in the questionnaires.

Results: Of the GPs, 589 (86%) responded; of the patients, 1202 (70%) responded. The most frequently reported suspected adverse reactions to sumatriptan reported by the GPs were dizziness (1.7%), nausea or vomiting (1.5%), drowsiness or sedation (1.4%), and chest pain (1.3%). The most frequently reported suspected adverse reactions by the patients were paraesthesia (11.7%), dizziness (8.1%), feeling of heaviness (8.0%), and chest pain (7.9%). Neither the GPs nor the patients reported serious adverse reactions.

Conclusions: First, patients experience significantly more suspected adverse reactions than are registered by their GP. In view of this higher frequency of reporting of suspected adverse reactions, postmarketing studies with data from GPs only, may underestimate the cumulative incidence of adverse reactions. Second, we conclude that it is possible to obtain useful additional information about adverse drug reactions from patients by sending them questionnaires via their GP.