ADMS 3502 Lecture Notes - Lecture 29: Diphenhydramine, Gq Alpha Subunit, Benadryl
21 May 2020
School
Department
Course
Professor
Roohi Sharma
Warnings Against the use of First-Generation Antihistamines
H1-receptors are G-protein coupled receptors that associate with Gq protein which
activates the PLC pathway (Togias S64). This pathway results in variety of downstream pro-
inflammatory processes including the expression of NF-kB transcription factor, dilation of blood
vessels leading to redness and bronchoconstriction (Nizamutdinova et al 3065). Antihistamines
or H1 receptors antagonist attenuate the endogenous histamine response. First generation H1-
antihistamines are not favorable as they have nonselective activity. They bind to various
receptors and cross the blood brain barrier to have a CNS effect causing sedation. Second
generation drugs like loratadine are polar and selective for peripheral H1 receptors (Thangam et
al 2).
Doctors warn against the use of first generation H1 antihistamines like Benadryl as they
are less effective and safe than second generation H1 antihistamine. For this reason, they suggest
making it behind the counter. Dr David Fisher, a clinical allergist says the medicinal ingredient
in Benadryl, diphenhydramine hydrochloride “makes you drowsy and irritable and if you take
too high a dose or an overdose, you will end up in hospital” (Ward, 2019).
I agree with the doctor on making first generation antihistamines behind the counter
where its use is regulated. Consumers may not be aware of the sedative effects of these drugs.
However, that is not to say that first generation antihistamines are not effective. These drugs,
providing a mild sedative effect will benefit patients who complain of sleep loss due to allergy
symptoms. Pharmacist can help assist patients in selecting the most appropriate allergy drug for
their need.
