chronopharmacology-Introduction

Now the medical science has well recognized the role played by biological rhythm on the effects of drugs. It is an established fact that rythmicity is an integral part of all life ,hence in drug administration, importance has to be given not only to the right substance of the right amount at the right place but also to the right time.
Not to speak of the optimum utilization of drugs given at the right time, even the onset of symptoms of certain diseases like asthma attacks, angina pectoris etc do not occur randomly with in 24 hours of the day. Drugs of different classes used as painkillers show periodic variations in their pharmacokinetics and can greatly depend on the time of the day.
The rhythmic phenomenon is shown even by the fundamental unit of life i.e., the cell. Fluctuation of their activity over a period of 24 hours is the circadian rhythm. The peaks and troughs of physiological functions are controlled by a set of pace makers called biological clocks or oscillators. Biological rhythms are genetically programmed and specific genes which code for circadian rhythm have been identified and located on chromosomes of drosophila . clock genes were identified in human tissues such as the skin and the mucosa.
In arthropods as well as mammals, neural formation has been identified as location of circadian oscillators. This in the case of the hypothalamic supra-chismatic nucleus ( SCN ) which in mammals appear to control production of ACTH and prolactin among other variables.
In humans biological clocks may also be located in the cortex of the brain . Periodic changes in the environment like light / dark, dusk / dawn, noise/ silence, heat/ cold etc act as signals to the organism to reset their biological clocks and synchronize their circadian rhythms. These periodic rhythms are called Zeitzebers. Zeitzebers only influence the rhythms but do not create them.
Biological rhythm is always a definite mathematical function and it can be quantified by certain parameters such as
The period T : It is the duration of one complete rhythmical variation and is expressed in units of time e.g. minutes, hours or days.
The Acrophase  : It is the mathematically estimated span of time taken to reach the crest of the validated rhythm for the period T under consideration. When T = 24 hours,  can be expressed in hours and minutes with midnight (0000), for example, as  .
The amplitude A : It is the amount of variability i.e. the crest to trough difference .
The Mesor M : It is the rhythm adjusted mean under the T under consideration.
The Frequency f : It is the number of cycles occurring in unit time.