Biologic rhythms and medicine.

Medical practice and research in the United States and other countries are pervaded by the traditional concepts of homeostasis. As a result, the time of day or year when a diagnostic or therapeutic procedure is performed or a drug is administered is not considered important. However, during the last three decades, the science of chronobiology has revealed the importance to medicine of the rhythms that exist in the biologic functions and processes of humans. This article reviews the basic concepts of human chronobiology and discusses the rhythm dependence of certain disease states and the pharmacodynamics of medications frequently prescribed for their treatment. Special reference is made to the nocturnal exacerbation of asthma and the use of chronobiologic principles in its treatment.