Dosage adjustments for antibacterials in obese patients - Applying clinical pharmacokinetics

Obesity is associated with physiological changes that can alter the pharmac okinetic parameters of many drugs. Vancomycin and the aminoglycosides are t he only antibacterials that have been extensively investigated in the obese population. The apparent volume of distribution (Vd) and total body cleara nce of vancomycin are increased in obese patients and have a better correla tion with total bodyweight (TBW) than with ideal bodyweight (IBW). The Vd o f aminoglycosides is increased in obesity and can be estimated from an adju sted bodyweight that accounts for a fraction of the excess bodyweight (TBW - IBW). These observed changes in pharmacokinetic parameters of vancomycin and aminoglycosides in obese patients may necessitate a deviation from the commonly recommended dosages administered to non-obese individuals. There are limited data regarding the pharmacokinetics of other antibacteria l classes in obese patients. The available information for cephalosporins s uggests that dosages may need to be increased in obese patients in order to obtain similar serum and tissue concentrations as in non-obese patients. A dditional pharmacokinetic studies of other antibacterial classes are requir ed in this special patient population.