The Sound of Evolution
Diphenhydramine
Mechanism of action:
Diphenhydramine is a first-generation antihistamine of the ethanolamine class. In the vestibular apparatus of the inner ear and its associated central nervous system pathways, when histaminergic neurons release histamine, activation of H1 receptors in these regions can further stimulate the brainstem vomiting center. Diphenhydramine reversibly blocks the binding of histamine to H1 receptors, thereby inhibiting histamine-induced neural signaling. Diphenhydramine also antagonizes muscarinic acetylcholine receptors, particularly M1 receptors. Between the vestibular system and the medullary vomiting center, acetylcholine is one of the major neurotransmitters.
Reference(s):
1. Raphael GD et al. (2006). Efficacy of diphenhydramine vs desloratadine and placebo in patients with moderate-to-severe seasonal allergic rhinitis. Ann Allergy Asthma Immunol.
2. Abdi A et al. (2014). Diphenhydramine overdose with intraventricular conduction delay treated with hypertonic sodium bicarbonate and i.v. lipid emulsion. West J Emerg Med.