Which protein is the primary carrier for basic drugs in plasma?

• A. Albumin
• B. Alpha-1 acid glycoprotein
• C. Haptoglobin
• D. Ceruloplasmin

Answer: (B)

Basic drugs in plasma are mainly bound by alpha-1 acid glycoprotein because this protein carries negative charges from sialic acid residues, making it a favorable partner for positively charged (cationic) drugs. The ionic interactions between the positively charged drug and the negatively charged binding sites on the glycoprotein reduce the free drug concentration, influencing distribution and clearance. Albumin tends to bind acidic or neutral drugs, due to its own negative surface charges, while haptoglobin and ceruloplasmin have other primary roles—haptoglobin binds free hemoglobin, and ceruloplasmin transports copper and acts as an enzyme—so they are not the main carriers for basic drugs. Be aware that alpha-1 acid glycoprotein levels can rise during inflammation, which can further affect how much basic drug is free versus bound and thereby impact pharmacokinetics.