Paper I
2023 July (Supplementary) (2019 Scheme) · 100 marks · 180 min

Question

Therapeutic uses of Anti-histamines.

Q124 marksShort Answers

Answer

H1 antihistamines block histamine’s action at H1 receptors, used across a range of allergic and non-allergic conditions:

  • Allergic rhinitis and conjunctivitis — block histamine-mediated sneezing, itching, and rhinorrhea (Cetirizine, Loratadine — second-generation, non-sedating).
  • Urticaria and angioedema — reduce histamine-mediated wheal-and-flare and itching.
  • Anaphylaxis — adjunct to adrenaline (never first-line alone, given onset is too slow for the acute emergency).
  • Motion sickness — first-generation agents with CNS penetration and antimuscarinic action (Promethazine, Dimenhydrinate).
  • Sedation/sleep aid — first-generation agents (Diphenhydramine), exploiting their CNS-depressant adverse effect therapeutically.
  • Antiemetic — first-generation agents (Promethazine), for vertigo/motion-sickness-related nausea.
  • Pre-anesthetic medication — Promethazine, for sedative and antisialagogue effect.

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