Pressure sores are a common occurrence in immobilized patients. They increase morbidity and mortality and impede rehabilitation. Antibiotics are routinely used to assist in effecting a cure when infection is present. Nevertheless, for patients with spinal cord injuries (SCI), strategies for effective therapy with antibiotics based on measurement of concentrations in tissue and pharmacokinetic behavior in extravascular spaces do not exist. By analyzing the concentration-time profile and protein binding of amikacin in the interstitial fluid (IF) in contact with pressure sores, we found that the disposition of amikacin in the tissue contiguous with pressure sores appears to be governed by simultaneous first-order and capacity-limited pharmacokinetic behavior. Amikacin disposition in IF proceeded without a simple relationship to amikacin concentrations in serum, and the time course in IF was not accurately simulated by linear models of amikacin pharmacokinetic behavior. Total amikacin clearance estimated from a pharmacokinetic model using simultaneous first-order and nonlinear intercompartmental transfer of amikacin was not significantly different from clearance calculated by us in a prior study of amikacin pharmacokinetic behavior in patients with SCI. In patients with SCI, optimal use of amikacin in the treatment of infected pressure sores is contingent upon accurate characterization of the pharmacokinetic behavior of this aminoglycoside in serum and in the IF in contact with these lesions. Only methods which quantitate amikacin concentration and protein binding in IF and incorporate a model that can simultaneously simulate nonlinear and linear disposition processes should be relied upon to influence therapeutic decision making.
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