According to the limited information available, exercise has no substantial
effect on the absorption of orally given drugs. However, it appears to enh
ance absorption from intramuscular, subcutaneous, transdermal and inhalatio
n sites. The effects of exercise on drug distribution are complex. Exercise
increases muscular blood flow resulting, for example, in the increased bin
ding of digoxin in working skeletal muscle. On the other hand, exercise may
sequester some drugs such as propranolol in muscle and reduce the availabi
lity of the drug for elimination. In addition, exercise decreases the clear
ance 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 concl
usion, if maintaining the plasma concentration of a drug at a certain level
is important, consideration should be given to alternative drugs if the pa
tient is on intermittent or irregular exercise.