Effect of exercise on plasma levels and urinary excretion of sulphadimidine and procainamide.

The pharmacokinetics of sulphadimidine (n = 9) and procainamide (n = 8), drugs which showed typical polymorphic acetylation rate, were studied in healthy volunteers subjected to intense physical exercise and bed rest for 4 hours in a cross-over manner. The exercise and the rest began 3 hours after giving procainamide and 4 hours after the administration of sulphadimidine, when the drug absorption had subsided. In rapid acetylators, the exercise raised both acetylated and non-acetylated sulphadimidine concentrations in serum, compared to rest values. With procainamide the rise was insignificant. In slow acetylators, the exercise revealed a significant difference in the procainamide group but not in sulphadimidine group. The exercise did not influence the acetylation degree of either of the drugs. Neither did it affect the protein binding of sulphadimidine. The urinary excretions of procainamide and acetylprocainamide were reduced by exercise generally more than those of sulphadimidine and acetylsulphadimidine. Endogenous creatinine clearance was reduced to 66%, whereas the renal clearances of sulphadimidine, acetylsulphadimidine and procainamide decreased to 89%, 48% and 16%, respectively. The results agree with our previous findings that physical stress can result in increased serum drug levels. Exercise does not seem to change the acetylation rate nor the protein binding of drugs, but it suppresses their excretion in urine, occasionally even more than what would be expected on the basis of the decrease in the glomerular filtration rate.