Which drug requires whole blood for monitoring?

• A. Tacrolimus
• B. Aminosalicylic acid
• C. Aspirin
• D. Ibuprofen

Answer: (A)

Monitoring concept: some drugs used in critical therapies require measuring the drug in whole blood because they bind extensively to blood cells. Tacrolimus fits this pattern because it binds strongly to red blood cells, so the amount present in whole blood better reflects the patient’s exposure and therapeutic effect than plasma alone. Measuring trough levels in whole blood helps you avoid underestimating the drug level and guides dosing to prevent rejection or toxicity in transplant patients.

Aminosalicylic acid, aspirin, and ibuprofen are not routinely monitored in whole blood for standard therapy. If monitoring is done, it’s usually in plasma or serum and not tied to the same red blood cell binding considerations that make whole-blood measurement essential for tacrolimus.