Elimination of procainamide in end stage renal failure

To investigate the effect of end stage renal insufficiency and hemodialysis on the serum half-life of procainamide, 500 mg of procainamide was given orally to control subjects and dialysis patients on interdialysis days. Procainamide was assayed by spectrophotometry and spectrophotofluorometry. Mean half-life in normal subjects was 3.2 hr by spectrophotometry and 3.5 hr by spectrophotofluorometry. Mean half-life in patients was 11.3 hr by spectrophotometry and 16.0 hr by spectrophotofluorometry (p less than 0.001 compared to control subjects). Half-life of procainamide during dialysis in patients given 500 mg of procainamide 1 hr before dialysis was 4.3 hr and 9.6 hr on a nondialysis day (p less than 0.001). Both methods of assay gave higher levels of procainamide when the metabolite, N-acetylprocainamide, was present in serum and the extract allowed to stand in 1 N HCl, but spectrophotometry was less affected. Thus, end stage renal insufficiency greatly prolongs the half-life of procainamide, procainamide is readily dialyzable, and N-acetylprocainamide is hydrolyzed in 1 N HCl to procainamide during routine serum determinations.