Which of the following describes the primary mechanism of action of hydroquinone in the treatment of melasma?
- A Competitive inhibition of the enzyme tyrosinase ✓
- B Acceleration of epidermal turnover through retinoid receptor binding
- C Chelation of copper ions at the active site of dopachrome tautomerase
- D Inhibition of plasminogen activator in keratinocytes
Correct answer: A. Competitive inhibition of the enzyme tyrosinase
Explanation
Hydroquinone is a structural analogue of tyrosine and acts as a competitive inhibitor of tyrosinase, the rate-limiting enzyme converting tyrosine to DOPA and dopaquinone. It also inhibits DNA and RNA synthesis in melanocytes, causing a reversible cytotoxic effect. Retinoid receptor binding describes tretinoin, plasminogen inhibition describes tranexamic acid, and copper chelation at tyrosinase describes kojic acid, which kills those distractors.
Reference: Fitzpatrick's Dermatology, 9th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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