4 Drug disposition and action in the burned patient

Thermal injury causes a prolonged, complex pathophysiological response which involves major changes in cardiovascular, renal and hepatic function. These changes, in addition to alterations in plasma protein concentrations, are responsible for significant changes in the disposition and action of many drugs in patients. Changes in drug absorption, plasma protein binding, hepatic blood flow and drug biotransformation, and renal blood flow, drug filtration and secretion have been demonstrated for many classes of drugs in burned patients. These pharmacokinetic factors often mean that standard therapeutic regimens may be inappropriate for such patients. In addition, burn injury may also cause a disruption of the functioning of drug receptors, causing altered pharmacological responses to plasma drug concentrations that are usually effective in non-burned patients. Such pharmacokinetic and pharmacodynamic changes have been observed in several classes of drugs used commonly in anaesthetic practice, these classes including the muscle relaxants, opioid analgesics, aminoglycoside antibiotics, benzodiazepines, exogenous catecholamines and H₂-receptor antagonists. Careful attention to the use of these agents in burned patients is required, with close monitoring of drug effect being particularly important.