Grapefruit juice—terfenadine single-dose interaction: Magnitude, mechanism, and relevance*

Abstract

A normal amount of regular-strength grapefruit juice produced maximum single-dose effects on terfenadine and carboxylic acid metabolite pharmacokinetics. The mechanism likely involved reduced presystemic drug elimination by inhibition of more than one metabolic pathway. The extent of the interaction was not sufficient to produce electrocardiographic changes. However, the pharmacokinetic effects were highly variable among individuals. This study further enhances the awareness of the potential for a serious interaction between grapefruit juice and terfenadine.