Although there is a paucity of data to guide dosing of antimicrobials in the critically ill obese patient, we can draw some conclusions from existing kinetic studies. Assuming normal renal and hepatic function, here's what to do:
Penicillins: Use the high end of dosing range. For example, if the plan is to use piperacillin/tazobactam 3.375 gm IV every 6 hours for a complicated intra-abdominal infection, use 4.5 gm instead.
Cephalosporins: Use the high end of the dosing range.
Carbapenems: Use the high end of the dosing range.
Quinolones: Use the high end of the dosing range.
Aminoglycosides: Dose using adjusted body weight. ABW (kg) = IBW + 0.4 X (actual body weight - IBW)
Vancomycin: 15-20 mg/kg actual body weight every 8 to 12 hours. Adjust based on trough level.
When dosing most antibiotics in critically ill obese patients, use the high end of the dosing range (if not more).
References
Erstad BL. Dosing of medications in morbidly obese patients in the intensive care unit setting. Intensive Care Med 2004;30(1):18-32. [PMID 14625670]
Medico CJ, Walsh P. Pharmacotherapy in the critical ill obese patient. Crit Care Clin 2010;26(4):679-88. [PMID 20970057]
