Emedastine (LY188695) is a second generation, selective histamine H1 receptor antagonist with anti-allergic activity. Emedastine reversibly and competitively blocks histamine by binding to H1 receptors, thus blocking its downstream activity. As a result this agent interferes with mediator release from mast cells either by inhibiting calcium ion influx across mast cell/basophil plasma membrane or by inhibiting intracellular calcium ion release within the cells. In addition, emedastine may also inhibit the late-phase allergic reaction mediated through leukotrienes or prostaglandins, or by producing an anti-platelet activating factor effect. Upon ocular administration, emedastine causes a dose-dependent inhibition of histamine-stimulated vascular permeability in the conjunctiva. Emedastine does not affect adrenergic, dopamine, or serotonin receptors.

Niaprazine is a histamine H1-receptor antagonist with marked sedative properties. Niaprazine has antihistamine and antiserotonin activities and can be used for sleep disorder research[1][2]. Niaprazine exhibits a low affinity for the vesicular monoamine transporter and for D2, α2, β, H1 and mAch receptors. Niaprazine, particularly the (+)stereoisomer, has a higher affinity for α1 (Ki = 77 nM) and 5-HT2 (Ki = 25 nM) binding sites, but is poorly recognized by 5-HT1A and 5-HT1B binding sites[2]. Niaprazine (60 mg/kg; i.p.; once) treatment increases rat brain 5-hydroxyindole acetic acid (5-HIAA) concentrations 30 min after treatment, and reduced them at 3-8 hr after treatment. Niaprazine also produces a short-lasting depletion of rat brain noradrenaline (NA) and dopamine (DA)[3]. Animal Model: Male Sprague-Dawley rats (150-200 g)[3] [1]. D Scherman, et al. Molecular pharmacology of niaprazine. Prog Neuropsychopharmacol Biol Psychiatry. 1988;12(6):989-1001. [2]. P G Rossi, et al. Niaprazine in the treatment of autistic disorder. J Child Neurol. 1999 Aug;14(8):547-50. [3]. P E Keane, et al. The effect of niaprazine on the turnover of 5-hydroxytryptamine in the rat brain. Neuropharmacology. 1982 Feb;21(2):163-9.

Sufotidine (AH 25352X) is a highly selective competitive H2 receptor antagonist.

Hydroxyzine Pamoate (Bobsule) is a histamine H1 receptor antagonist that is effective in the treatment of chronic urticaria, dermatitis, and histamine-mediated pruritus. Unlike its major metabolite CETIRIZINE, it does cause drowsiness. It is also effective as an antiemetic, for relief of anxiety and tension, and as a sedative.

Imetit dihydrobromide is a high affinity and effective agonist of histamine H3 and H4 receptors (Ki: 0.3 and 2.7 nM). Imetit mimics the histamine effect in triggering a shape change in eosinophils (EC50: 25 nM).