Disopyramide: serum level and arrhythmia conversion.

The response of arrhythmias to oral disopyramide in relation to its serum levels has been documented. Disopyramide (100 mg.) was given orally, 6 or 8 hourly, to 16 patients with coronary or hypertensive heart disease who developed acute but stable cardiac arrhythmias (20 episodes) which persisted, despite bed rest and sedation with intravenous diazepam or diamorphine. Blood was taken when arrhythmia conversion was observed and the serum disopyramide levels were estimated by gas chromatography. Over-all control of arrhythmias was achieved in 13 (82 per cent) patients within 24 hours. Disopyramide-serum levels were as follows: effective for atrial arrhythmias, 2.80 to 3.18 mug per milliliter, and 3.27 to 7.48 mug per milliliter for ventricular; mean effective levels for all arrhythmias, 3.69 mug per milliliter; mean ineffective levels, 2.39 mug per milliliter (p less than 0.01). Side effects (prolongation of PR and QTc, fall of diastolic BP, urine retention) were observed with serum levels of 3.61 to 7.48 mug per milliliter (mean, 5.54 mug per milliliter) but they were not troublesome clinically. It is concluded that disopyramide is effective and safe with serum levels ranging from 2.39 to about 3.60 mug per milliliter, and this can be maintained with 100 mg., 8 hourly. The drug, however, should be given with caution to patients with severe myocardial disease or low arterial pressure and in the presence of an abnormal ECG.