The altered pharmacokinetics and pharmacodynamics of drugs commonly used in critically ill patients.

The critically ill patient occupies an increasing amount of time and bed space in modern hospital practice, and also commands increasing expenditure. Drug therapy in these patients has, in the past, been based on data derived from healthy volunteers, fit anaesthetised patients undergoing minor operative procedures, or patients with single organ failure. Alterations in pharmacokinetics and pharmacodynamics have not been studied in depth in critically ill patients who often have multisystem failure. This paper reviews the currently available information on drugs in common usage in these patients. The studies that have been performed have usually shown delayed drug clearance, altered volumes of distribution and prolonged elimination half-lives. The sedative and analgesic drugs, in particular, have shown marked accumulation which may confuse the clinical picture, and prolonged periods of assisted ventilation may be required until the drugs are eliminated.