Low-dose procainamide: low risk of complications with long-term use.

The incidence of procainamide-induced drug reactions was studied prospectively in 55 patients receiving long-term therapy with a mean duration of 23 months. New symptoms that occurred in 13 patients after the drug was started were similar to complaints presented by 25 patients before the medication was started. Duration of therapy was positively correlated with new symptom occurrence (P < .05) but not with age, sex, dose, or dose interval. Other concomitant drugs did not influence the results. Antideoxyribonucleoprotein antibodies were positive in 27 patients (55 percent) and in seven of 13 with new symptoms; female sex (P < .05) and increasing age (P < .05) favored a positive test. Anti-DNA antibodies were not found in any patients. Procainamide, at a mean dose of 1.5 g/day, was judged to be therapeutically effective by the clinic staff independent of this study; the drug was not discontinued in any patient because of the severity of symptoms.