The effects of exercise on the pharmacokinetics of drugs.

According to the limited information available, exercise has no substantial effect on the absorption of orally given drugs. However, it appears to enhance absorption from intramuscular, subcutaneous, transdermal and inhalation sites. The effects of exercise on drug distribution are complex. Exercise increases muscular blood flow resulting, for example, in the increased binding of digoxin in working skeletal muscle. On the other hand, exercise may sequester some drugs such as propranolol in muscle and reduce the availability of the drug for elimination. In addition, exercise decreases the clearance of highly extracted drugs and increases their plasma concentration. It may also increase the clearance of drugs by increasing biliary excretion. Since exercise reduces renal blood flow, the plasma concentrations of those drugs which are primarily eliminated by the kidneys may increase. In conclusion, if maintaining the plasma concentration of a drug at a certain level is important, consideration should be given to alternative drugs if the patient is on intermittent or irregular exercise.