This report reviews a contemporary methodology for determining antibiotic dosage modifications among patients with renal impairment. Historically, the approach to identifying renal dosage adjustments has focused on achieving comparable concentration-time profiles between patients with renal impairment and those with normal kidney function. While this approach is intuitive, it fails to incorporate the relationship between antibiotic exposure and effect in the renal dose selection process. A candidate renal dosing scheme that is worthy of incorporation into clinical practice should balance the probability of achieving the exposure target associated with success against the risks of toxicity and the emergence of resistance. This review describes a methodology for optimally identifying dosage adjustments in patients with impaired renal function using extended-infusion piperacillin/tazobactam as an illustrative example.