Quinidine Excretion in Aciduria and Alkaluria

Quinidine toxicity may develop unexpectedly when the urine becomes alkaline in disease or during alkalinizing therapy. Excretion of quinine, the optical isomer of quinidine, is known to be retarded by urine alkalinization. These observations prompted study of quinidine excretion as a function of urine pH. Four subjects were given constant quinidine dosage with the pH and quinidine concentration of blood and urine determined during aciduria and alkaluria. The results indicated that excretion of quinidine varied inversely with urine pH. With urine pH <6.0, average quinidine excretion was 115 ± 84 mg/liter; for pH >7.5 average excretion was 13 ± 8 mg/liter (P < 0.001). Total daily excretion of quinidine was also reduced significantly. Blood pH did not change significantly, but quinidine clearance decreased 50%, and serum quinidine concentration and Q-T interval increased during alkalinization. These results are discussed in light of several theories of renal excretion of quinidine.