The Role of Antihistamines in the Treatment of Vasomotor Rhinitis

Table 3 Relative Histamine Receptor Binding Affinities (Ki) for Selected H1 Antagonists

H1 Antagonist	H1 Receptor (nM)	H2 Receptor (nM)	H3 Receptor (nM)
Ketotifen	1.3	1155	2277
Emedastine	1.3	49,067	12,430
Desloratadine	4	ND	ND
Cetirizine	6.3	ND	ND
Azelastine	6.8	ND	ND
Epinastine	9.8*	4030*	ND
Diphenhydramine	12.5	1600	25,000
Olopatadine	32	100,000	79,400
Loratadine	35	ND	ND
Levocabastine	56	23,500	4597
Fexofenadine	83	ND	ND
Pyrilamine	0.8	9510	1016
Chlorpheniramine	1.4	7980	3103
Pheniramine	34	14,567	10,567
Antazoline	38	44,433	42,400
Ranitidine	46,100	187	10,537
Cimetidine	6190	2377	20,750
Thioperamide	280,000	57,967	1.1
Methylhistamine	138,000	72,100	1.4
Histamine	180,000	18,350	4.5

Ki is the dissociation constant based on the Cheng-Prussof equation, Ki 1/4 IC50/(1 Þ L/Kd), such that a lower value denotes higher affinity binding. IC50 is the concentration of drug needed to produce 50% inhibition of the receptor binding.
The lower the value the higher the affinity (13).
ND, no data.
*Reported as the IC₅₀.

ISSN: 1939-4551