Ophthalmic antihistamines and H1-H4 receptors

Area of Science:

• Pharmacology
• Allergy Research
• Drug Discovery

Background:

• Antihistamines target four histamine receptors (H1-H4) with varying affinities.
• Receptor binding determines antihistamine efficacy and potential side effects.
• Understanding relative potencies is crucial for optimizing allergy treatment.

Purpose of the Study:

• To determine the relative potency of various antihistamines.
• To compare binding affinities of antihistamines across H1, H2, H3, and H4 receptors.
• To identify the most and least potent antihistamines for each receptor subtype.

Main Methods:

• Systematic review of studies reporting antihistamine binding affinities.
• Analysis of dissociation constant for inhibitor binding (Ki) values.
• Comparative assessment of nineteen antihistamines against H1-H4 receptors.

Main Results:

• Pyrilamine showed the highest affinity for H1 receptors (Ki = 0.8 nM); thioperamide had the lowest (Ki = 280,000 nM).
• Ranitidine was most potent for H2 receptors (Ki = 187 nM); olopatadine was least potent (Ki = 100,000 nM).
• Thioperamide demonstrated highest affinity for H3 (Ki = 1.1 nM) and H4 (Ki = 27 nM) receptors; olopatadine and cimetidine/ranitidine showed lowest affinity for H3 and H4, respectively.

Conclusions:

• This review establishes the relative potencies of antihistamines based on receptor binding affinities.
• Sparse data for H4 receptor binding necessitates further investigation.
• Future research into histamine receptor subtypes may lead to more effective allergy treatments, including for ocular surface conditions.