Phenytoin toxicity due to concomitant antituberculosis therapy.

Isoniazid inhibits the metabolism of phenytoin. Slow acetylators, who comprise roughly 50% of the South African population, are likely to develop clinical and biochemical features of phenytoin toxicity when this drug is given together with antituberculosis therapy. We describe a patient in whom this interaction caused a series of dangerous clinical events. Seventy-four per cent of patients with epileptogenic disorders seen at the Emergency Unit at Groote Schuur Hospital were on phenytoin and 11.6% of these had blood levels in the toxic range. The wide use of phenytoin during the recent tuberculosis epidemic makes it imperative to suspect this drug interaction in patients exhibiting clinical features that might be related to phenytoin toxicity. Knowledge of this interaction and adjustment of the dose of phenytoin should enable clinicians to avoid this adverse drug interaction.

A prospective study of electrical cardioversion for sustained tachycardias by emergency unit personnel.

Acute symptomatic tachyarrhythmias are commonly seen by emergency unit personnel. Electrical cardioversion is often used at Groote Schuur Hospital to treat such patients because of concerns about the safety and efficacy of intravenous anti-arrhythmic agents. All patients presenting with acute symptomatic tachyarrhythmias who were managed only by the staff of the Emergency Unit were entered into the study to assess the efficacy and safety of direct current (DC) cardioversion. Those with sinus tachycardia or atrial fibrillation of more than 24 hours' duration were excluded. Staff, on joining the unit, were instructed in the use and technique of DC cardioversion, and given simple guidelines for the management of acute tachyarrhythmias. Fifty-three patient events were seen over a period of 16 months: 7 patients had ventricular tachycardia, 21 had atrial flutter, 20 had paroxysmal junctional re-entry tachycardia, 4 had atrial fibrillation and 1 had multifocal atrial tachycardia. Fifty-two were successfully converted to sinus rhythm. One patient with atrial flutter and 9 with paroxysmal junctional re-entry tachycardia reverted after undergoing vagal manoeuvres or receiving intravenous verapamil. Of the remaining 43 patients, 42 (98%) were cardioverted with synchronised DC shock under midazolam sedation (7/7 ventricular tachycardia, 20/20 atrial flutter, 11/11 paroxysmal junctional re-entry tachycardia, 4/4 atrial fibrillation, 0/1 multifocal atrial tachycardia). Four patients had their sedation electively reversed with flumazenil. No complications occurred. DC cardioversion was only considered inappropriate in the 1 patient with multifocal atrial tachycardia. This study shows that if simple guidelines are followed, non-cardiologist junior medical personnel can safely and effectively manage sustained, acute, symptomatic tachyarrhythmias by employing DC cardioversion as and when appropriate.