Measurement of plasma disopyramide as a guide to paediatric use.

We have studied the relationship between age, daily dose, plasma concentration and clinical efficacy of disopyramide in a group of paediatric patients. Twelve children with ventricular and 3 with supraventricular arrhythmias were treated with oral disopyramide. The initial dose was 3-6 mg/kg per day. This was adjusted until a pre-dose plasma concentration greater than 2 mg/I was achieved. Seven patients were judged to have responded to the treatment on clinical criteria. No symptoms or signs of toxicity were observed. In some of the children the dose of disopyramide required to achieve a plasma concentration greater than 2 mg/l was greatly in excess of the normal adult dose. Generally the youngest children required the highest dose, but the variation was wide. The dose could not be predicted from the age, the body weight or the surface area of the patient. In children high doses of disopyramide may be needed to achieve effective plasma concentrations of the drug; such doses are not associated with adverse effects. Measurement of the plasma concentration is necessary to guard against premature termination of therapy.