Accumulating clinical evidence suggests that there are significant inter-individual differences in the efficacy of standard treatment protocols used for a variety of diseases, including diabetes, hypertension, depression, cancer, and epilepsy, as well as differences in drug-related side effects and toxicity. When multidrug therapy regimens are used, the issue frequently becomes more apparent. The causes for this variation appear to be connected to the multi-factorial regulation of the machinery governing drug destiny and biological activity in the body. This machinery includes cell-signaling, metabolic, and transport systems, which are encoded by their respective genes and, in turn, are controlled by a variety of parameters such as age, gender, race, lipidemic, and endocrinological status. The respiratory, immunological,cardiovascular,gastrointestinal,endocrinological, and central neurological systems all play important modulatory roles in the machinery that regulates drug action.
External modifying variables such as stress, nutrition, ambient chemicals, toxicants, and medications, as well as infectious disorders, can all influence the result and toxicity of pharmacotherapy by changing the pharmacokinetic and pharmacodynamics profiles of pharmaceuticals. This is due to the fact that they can interfere with medication absorption, distribution, metabolism, excretion, and action. In this regard, stress is important in the multifactorial control of medications in the body and in shaping a drug's pharmacokinetic profile since it affects many enzymes that catalyze the metabolism of the majority of prescription pharmaceuticals.
