Pharmacokinetic and pharmacodynamic monitoring of the elderly in critical care.
The cases presented illustrate the clinical application of several of the common pharmacokinetic and pharmacodynamic changes in the elderly. The number of drugs that must be used with caution in the aging person is potentially quite large. In addition, there are numerous other diseases that can result in additional changes in drug absorption, distribution, metabolism, excretion, and target-organ effect. These conditions are particularly prevalent in the elderly patient in the critical care setting, and include the systemic inflammatory response syndrome, sepsis, acute renal failure, diabetic ketoacidosis, and the postoperative state. It must be emphasized, however, that the elderly are not a homogeneous group. The rate of decline of many physiologic functions varies widely. Chronic diseases and lifestyle alterations are additional variables that affect the function of many body systems. Furthermore, it is likely that the different pharmacokinetic and pharmacodynamic parameters discussed in this article do not all change to the same degree in a given individual. Pharmacologic therapy, therefore, always will be quite empiric in elderly patients. There is no substitute for meticulous monitoring of the patient using every available modality. This is particularly crucial in the critical care setting, where drugs can be lifesaving and life threatening at the same time.