Kd: 0.8 nM (Histamine H1 receptor), 5200 nM (Histamine H2 receptor), >3000 nM (Histamine H3 receptor)
pKd: 9.4 (Histamine H1 receptor)

Mepyramine maleate is an antagonist of histamine H1 receptor, with K _d s of 0.8 nM, 5200 nM and >3000 nM for H1, H2, and H3 receptor, respectively, and a pK _d of 9.4 for H1 receptor. Mepyramine binds to the H1 receptor with different K _d s in Guinea pig brain (0.8 nM), rat brain (9.1 nM) and DDT1-MF-2 and BC3H1 cell (276 nM). Mepyramine decreases the InsP levels in CHO-gpH1 cells, with log EC ₅₀ of -7.94 ± 0.11, and reduces the the maximal response to ATP in CHO-gpH1 cells.

Mepyramine obviously decreases the second phase of nociceptive response via i.p at 10 and 20 mg/kg, but shows no significant effect at 5 mg/kg in rats.