An 18-month-old has several tan-brown macules on the trunk that become raised, itchy wheals when rubbed firmly. One larger nodule blistered after friction from clothing. Serum tryptase is mildly elevated. Parents ask which medications should be avoided. Which class poses the greatest risk?

• A Opioid analgesics and other mast cell degranulating drugs ✓
• B Amoxicillin-type antibiotics
• C Paracetamol-based antipyretics
• D Non-sedating antihistamines

Explanation

Darier sign, a wheal-and-flare response to stroking a pigmented macule or nodule, establishes cutaneous mastocytosis (urticaria pigmentosa). Mast cells in the lesions release histamine when provoked by rubbing, temperature changes, or degranulating drugs such as opioids, codeine, vancomycin, and radiographic contrast media, which can precipitate flushing, hypotension, or shock. Non-sedating antihistamines are the mainstay of therapy and paracetamol is considered safe, so options C and D are protective rather than harmful.

Reference: Hurwitz Clinical Pediatric Dermatology, 5th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.