The pharmacovigilance of olanzapine: results of a post-marketing surveillance study on 8858 patients in England.

Olanzapine is an 'atypical' antipsychotic indicated for the treatment of schizophrenia. We analysed adverse events (AEs) reported in primary practice in England. Dispensed prescriptions issued between December 1996 and May 1998 provided exposure data. Questionnaires sent to general practitioners provided outcomes. Frequently reported AEs were: drowsiness/sedation (n = 19), extrapyramidal disorder (n = 13) and unspecified side-effects (n = 33). Events with highest incidence density in first month and reason for stopping were: drowsiness/sedation [n = 153, incidence density (ID)1 18.9], weight gain (n = 117, ID1 8.9) and malaise/lassitude (n = 65, ID1 5.2). Extrapyramidal disorders were more common in elderly population (> 70 years, ID1 3.6, risk 26.0 per 1,000 patients) compared to < 70 years (ID1 1.1, risk 8.4 per 1,000 patients). Serious suspected adverse reactions were neuroleptic malignant syndrome (n = 1) and angioneurotic ooedema (n = 2). There were eight reports of diabetes mellitus assessed as possibly due to olanzapine. Diabetes mellitus was an unlabelled AE and possible signal generated by prescription-event monitoring.