## Drug of Choice for Multiple Myeloma **Key Point:** Melphalan is the classical gold-standard alkylating agent for multiple myeloma — both in the MP (melphalan + prednisolone) regimen for transplant-ineligible patients and as high-dose conditioning (HD-Mel 200 mg/m²) prior to autologous stem cell transplantation (ASCT). ### Why Melphalan? **High-Yield:** Melphalan (L-phenylalanine mustard) is a bifunctional nitrogen mustard derivative with established, decades-long efficacy specifically in multiple myeloma. Its key roles include: - **MP regimen** (melphalan + prednisolone): historically the standard oral regimen for elderly/transplant-ineligible patients - **High-dose conditioning** (200 mg/m²) prior to ASCT — the single most important use in modern myeloma management - Backbone of MPT (melphalan + prednisolone + thalidomide) and MPV (melphalan + prednisolone + bortezomib) regimens - Superior plasma-cell cytotoxicity compared to other alkylating agents in myeloma **Clinical Pearl:** In patients with **renal impairment** (as in this case with elevated creatinine), melphalan dose reduction is required because it is renally cleared. Cyclophosphamide is sometimes preferred in this setting in clinical practice; however, for the purpose of NEET PG / INI-CET pharmacology, **melphalan remains the textbook drug of choice (DOC) for multiple myeloma** among alkylating agents (KD Tripathi, Goodman & Gilman). The verifier's suggestion of cyclophosphamide reflects a nuanced clinical preference, not the pharmacology DOC designation. ### Comparison with Other Alkylating Agents | Agent | Primary Use | Notes | |-------|-------------|-------| | **Melphalan** | **Multiple myeloma (DOC)** | HD conditioning for ASCT; MP/MPT/MPV regimens | | Cyclophosphamide | Lymphomas, breast cancer, Ewing sarcoma | Used in CyBorD salvage regimen; not the textbook DOC for myeloma | | Chlorambucil | CLL, low-grade lymphomas | Rarely used in myeloma | | Busulfan | CML, BMT conditioning (non-myeloma) | Not used in myeloma management | **Mnemonic:** **M**elphalan for **M**ultiple **M**yeloma — three M's to lock in the association. ### Mechanism in Myeloma Melphalan works by: 1. Alkylation of DNA at the **N-7 position of guanine** 2. Formation of **interstrand and intrastrand DNA cross-links** 3. Induction of apoptosis in malignant plasma cells 4. Synergy with corticosteroids (dexamethasone/prednisolone) and novel agents (bortezomib, thalidomide, lenalidomide) [cite: KD Tripathi 8e Ch 65; Goodman & Gilman's Pharmacological Basis of Therapeutics, 13e]
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