Under alkaline conditions, which is the primary drug transport protein?

• A. Albumin
• B. Acid-Glycoprotein
• C. Transferrin
• D. Haptoglobin

Answer: (A)

The main idea is that albumin is the dominant carrier for many drugs in plasma. At higher pH, acidic drugs lose a proton and carry a negative charge, which fits well into albumin’s binding sites and leads to strong binding. This makes albumin the primary drug transport protein under alkaline conditions because it handles most of the drug binding in the blood. Other proteins have specific roles—alpha-1-acid glycoprotein binds basic drugs, transferrin transports iron, and haptoglobin binds free hemoglobin—but they’re not the general carriers for drugs like albumin is.