Extrapyramidal reactions to prochlorperazine and haloperidol in the United Kingdom

The epidemiology of extrapyramidal reactions to prochlorperazine and haloperidol in the United Kingdom has been studied using reports in the Adverse Reactions Register of the Committee on the Safety of Medicines (CSM) and from general practitioner prescribing data. Between 1967 and 1982 there were an estimated 37.0 million prescriptions for prochlorperazine and 3.2 million for haloperidol; in this time there were 104 reports of adverse reactions to prochlorperazine and 62 to haloperidol. The predominant extrapyramidal reaction reported was dystonia-dyskinesia (99 reports for prochlorperazine and 47 for haloperidol). The remaining reactions reported were of Parkinsonism. Dystonia-dyskinesia usually occurred within three days of commencing treatment, and for both drugs the incidence, expressed per million prescriptions, varied significantly with age, the highest incidence being in patients under 20 years. Thus young patients appear at particular risk of acute extrapyramidal reactions to dopamine receptor antagonists.