Phenytoin-Dexamethasone Interaction

ABSTRACT

A possible drug interaction between phenytoin and dexamethasone was evaluated by comparing serum phenytoin concentrations in 34 patients receiving both drugs with those if a control group 19 patients receiving phenytoin only. Serum phenytoin concentrations obtained 24 hours after a loading dose of 15mg per kilogram body weight administrated intravenously were examined. The serum concentrations of phenytoin were checked by homogenous enzyme immunoassay(EMIT) method. The total amounts of dexamethasone administered during the 24 hours period ranged from 10 to 40mg. The average serum phenytoin concentration was 12.08+/-2.78 microgram/ml in patients receiving both drugs, as compared to 8.58+/-2.72 microgram/ml in patients receiving phenytoin only(p<0.005). Our results suggest that serum phenytoin concentrations in patients receiving both drugs were higher than in patients receiving phenytoin only.