A Postmarketing Surveillance Study of Gabapentin as Add‐on Therapy for 3,100 Patients in England

Summary:  Purpose: Our aim was to monitor the use of gabapentin (GBP) by patients prescribed this drug by primary care physicians in England soon after it was marketed in the United Kingdom. Methods: A noninterventional observational cohort study was conducted by using the technique of prescription‐event monitoring. Patients were identified from dispensed National Health Service prescriptions. Outcome data were obtained from questionnaires sent to the doctor ∼6 months after the initial prescription. These data included demographic information, events reported since starting GBP, and reason for stopping the drug, if it was stopped. Incidence rates were calculated for given periods for all events reported. Additional information was requested for selected events of medical interest, including pregnancies. Standardised mortality ratio (SMR) was calculated. Results: The cohort comprised 3,100 patients, of whom 136 (4%) were children. The median duration of treatment was 8.1 months. The most frequently reported adverse events reported during the first month of treatment, drowsiness/sedation, dizziness, and malaise/lassitude, also were the commonest reasons for discontinuing GBP and reported as suspected adverse drug reactions (ADRs). There were no congenital anomalies in the 11 babies born to women who used GBP during the first trimester of pregnancy. Crude mortality rate was 5 times that in general population but similar to that in other published studies. Conclusions: Neurologic‐related events were the most frequently reported adverse events. They also were the commonest reasons for discontinuing treatment and reported as suspected ADRs. No previously unrecognised adverse events were detected in this large cohort of patients who were among the first treated with gabapentin in England.