PHENIRAMINE - A MUCH ABUSED DRUG

Objectives: To assess the relative clinical toxicity of phenlramine co mpared with other antihistamines taken in overdose and its relative us e for self-poisoning. Design: A prospective follow-up cohort study of antihistamine self-poisonings. Local pharmacists were surveyed to asce rtain the approximate market share of pheniramine. Setting: Newcastle, Australia. Subjects: 102 patients giving rise to 118 consecutive admi ssions to hospital for antihistamine self-poisoning after ingestion of pheniramine (43) or other antihistamines (75). Main outcome measures: Generalised seizures, delirium/psychosis, sedation, QRS width, mean b lood pressure. Results: Pheniramine accounted for only 3.0% of antihis tamine items dispensed, 5.5% of defined daily doses (DDDs) dispensed, but133.g% of antihistamine self-poisonings. Fourteen admissions were c omplicated by seizures and 43 by delirium/psychosis. Patients admitted after ingestion of pheniramine were more likely to have generalised s eizures (13 of 43) than those ingesting other antihistamines (one of 7 5). Other complications (sedation, need for ventilation, prolongation of QRS interval, change in blood pressure) were comparable. A very hig h proportion of the pheniramine group had a history of drug or alcohol abuse (79.9%). This included 60.5% with a history of antihistamine ab use. The figures for those who ingested other antihistamines were 46.7 % and 6.7% respectively. Conclusions: Pheniramine is taken in overdose more frequently than other antihistamines relative to Its market shar e. It is also more likely to be abused than other antihistamines. In o verdose, it appears to be more proconvulsant than other antihistamines . Consideration should be given to the use of alternative antihistamin es in patients at risk of seizures. In the light of these findings, re gulatory authorities should review the over-the-counter availability o f pheniramine.