A 60-year-old man with newly diagnosed primary central nervous system lymphoma is planned for high-dose methotrexate-based therapy, with carmustine added to the regimen. The principal rationale for choosing carmustine over other alkylating agents in intracranial tumours is:

• A It is activated selectively within tumour cells by glutathione transferase
• B Its high lipid solubility permits penetration across the blood-brain barrier ✓
• C It is the only alkylator that cross-links DNA rather than alkylating single bases
• D It undergoes renal elimination, avoiding hepatic first-pass metabolism

Explanation

Carmustine is a nitrosourea whose marked lipid solubility allows it to cross the blood-brain barrier, making the nitrosoureas the classical alkylators for brain tumours. All bifunctional alkylating agents including nitrogen mustards form interstrand DNA cross-links, so option C is false. Nitrosoureas actually cause delayed myelosuppression and pulmonary fibrosis; activation is spontaneous decomposition, not enzyme-mediated tumour selectivity.

Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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