Question

A 68-year-old woman is admitted to the hospital with a complicated intra-abdominal infection. She is started on a newly approved intravenous antimicrobial agent. The standard maintenance dose of this medication for patients with normal renal function (defined as a creatinine clearance of $100 \text{ mL/min}$) is $600 \text{ mg}$ administered every 24 hours. Pharmacokinetic data indicate that in healthy individuals, $60\%$ of the drug is eliminated unchanged in the urine, while the remaining $40\%$ undergoes hepatic metabolism. The patient's basic metabolic panel reveals an elevated serum creatinine, and her creatinine clearance is estimated to be $25 \text{ mL/min}$. Assuming linear pharmacokinetics and normal hepatic function, what should be the new daily maintenance dose in $\text{mg}$ to achieve the same steady-state average drug concentration as a patient with normal renal function?