Unusual evidence of myocardial involvement during a hypersensitivity reaction to oral penicillin.

A hypersensitivity reaction to orally administered phenoxymethyl penicillin is reported. The manifestations of the reaction included fever, arthralgia, urticaria and an irregular pulse. Serial ECG showed second-degree atrioventricular block with junctional escape beats, an atypical Wenckebach pattern and, finally, first-degree atrioventricular block with gradually decreasing PR intervals. A normal tracing was recorded on the sixth day despite the persistence of the rash and joint pains.