Hemodialysis for severe procainamide toxicity: clinical and pharmacokinetic observations

A 67-yr-old woman who ingested approximately 7 gm procainamide developed severe hypotension, renal insufficiency, and life-threatening cardiac toxicity. Hemodialysis doubled the rate of procainamide elimination and increased fourfold the clearance of NAPA, the N-acetylated metabolite of procainamide. Observations of procainamide and N-acetylprocainamide (NAPA) plasma levels during the patient's recovery suggest that lethargy and profound hypotension can be expected when these levels total 60 mug/ml and that severe cardiac toxicity should be anticipated with levels totaling 42 mug/ml or more. Hemodialysis also permitted investigation of the effects of hypotension on the pharmacokinetics of these compounds. The apparent volume of procainamide distribution was reduced from a normal value of 2 L/kg to 0.76 L/kg, and that of NAPA from 1.4 L/kg to 0.63 L/kg. The elimination + 1/2 of procainamide was prolonged from the normal of 3 hr to 10.5 hr, and that of NAPA from 6 to 35.9 hr. Procainamide absorption was also slowed in this clinical setting, causing procainamide plasma levels to continue rising for some time after toxicity was first recognized.