A 68-year-old male, weighing 70 kg, with a creatinine of 180 micromol/L, is admitted to hospital for community-acquired pneumonia. His current medications include metformin 1000 mg BID, ramipril 5 mg daily, and atorvastatin 40 mg daily. The physician wants to initiate piperacillin-tazobactam 4.5 g IV every 8 hours. Based on his renal function, what is the most appropriate dosage adjustment for piperacillin-tazobactam?

Question: A 68-year-old male, weighing 70 kg, with a creatinine of 180 micromol/L, is admitted to hospital for community-acquired pneumonia. His current medications include metformin 1000 mg BID, ramipril 5 mg daily, and atorvastatin 40 mg daily. The physician wants to initiate piperacillin-tazobactam 4.5 g IV every 8 hours. Based on his renal function, what is the most appropriate dosage adjustment for piperacillin-tazobactam?

Answer options:

• No dose adjustment is needed, continue 4.5 g IV every 8 hours.
• Change to 3.375 g IV every 8 hours. ✅ Change to 4.5 g IV every 12 hours.
• Change to 3.375 g IV every 12 hours.

Correct answer: Change to 4.5 g IV every 12 hours.

Explanation: First, calculate CrCl using Cockcroft-Gault: CrCl = [(140 - 68) * 70] / (180 * 0.814) = 34.6 mL/min. For CrCl 20-40 mL/min, the recommended dose for piperacillin-tazobactam (normal dose 4.5 g q8h) is 4.5 g every 12 hours. Therefore, the frequency should be extended.