Pheniramine--a much abused drug.

OBJECTIVES

To assess the relative clinical toxicity of pheniramine compared with other antihistamines taken in overdose and its relative use for self-poisoning.

DESIGN

A prospective follow-up cohort study of antihistamine self-poisonings. Local pharmacists were surveyed to ascertain the approximate market share of pheniramine.

SETTING

Newcastle, Australia.

SUBJECTS

102 patients giving rise to 118 consecutive admissions 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 blood pressure.

RESULTS

Pheniramine accounted for only 3.0% of antihistamine items dispensed, 5.5% of defined daily doses (DDDs) dispensed, but 33.9% of antihistamine self-poisonings. Fourteen admissions were complicated by seizures and 43 by delirium/psychosis. Patients admitted after ingestion of pheniramine were more likely to have generalised seizures (13 of 43) than those ingesting other antihistamines (one of 75). Other complications (sedation, need for ventilation, prolongation of QRS interval, change in blood pressure) were comparable. A very high proportion of the pheniramine group had a history of drug or alcohol abuse (79.9%). This included 60.5% with a history of antihistamine abuse. 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 share. It is also more likely to be abused than other antihistamines. In overdose, it appears to be more proconvulsant than other antihistamines. Consideration should be given to the use of alternative antihistamines in patients at risk of seizures. In the light of these findings, regulatory authorities should review the over-the-counter availability of pheniramine.