Procainamide

Procainamide is associated with the highest incidence of lupus of any available drug. The incidence varies by study. This is probably because the incidence increases with time over a period of years. The average time to onset for slow acetylators is 12 months, but that for rapid acetylators is 48 months (Woosley et al. 1978). The incidence with prolonged therapy is close to 30% (Henningsen et al. 1975). The incidence of ANA development is even higher: more than 90% with chronic therapy (Woosley et al. 1978). However, most patients with procainamide-induced ANAs are asymptomatic, so there is no rationale for monitoring ANAs in asymptomatic patients. Pleurisy and pulmonary infiltrates seem to be somewhat more common in pro-cainamide-induced lupus than in lupus associated with other drugs. Patients who develop procainamide-induced lupus can be treated with N-acetylprocainamide, a major metabolite of procainamide, although a small amount of this drug is converted back to procainamide (Stec et al. 1979).

Since the CAST study found that this class of antiarrhythmic agents actually increases mortality due to cardiac arrhythmias, the use of procainamide and many other antiarrhythmic agents has decreased significantly (CAST 1989). Procainamide use is also associated with a relatively high incidence of agranulocytosis, which further discourages its use. Therefore, procainamide-induced lupus is now less of an issue than it was a decade or two ago.

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