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.