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 spectrophotojiuorometry. Mean half‐life in normal subjects was 3.2 hr by spectrophotometry and 3.5 hr by spectrophotojiuorometry. Mean half‐life in patients was 11.3 hr by spectrophotometry and 16.0 hr by spectrophotojiuorometry (p < 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 < 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 HCI to procainamide during routine serum determinations.