[Biological rhythms and medications: a source of variability often neglected in pharmacology]

Several factors are known to induce changes in pharmacological response to drugs. The existence of biological rhythms is often neglected when assessing drug effects. Nevertheless, the best knowledge of biological rhythms have lead to medical applications, particularly chronopharmacology. Drug tolerance as well as drug effects are changing according to the hour of administration. These chronopharmacological phenomena may be explained by temporal changes in receptors drug binding or transductional effects, as well as pharmacokinetic variations in absorption, distribution, metabolism and elimination according to the moment of administration. Medical applications of such findings lead to choose the best moment of administration of the drug in order to improve the benefit/risk ratio.