Antihistamine-1 is an H1-antihistamine (Ki: 6.9 nM) with acceptable blood-brain barrier penetration and also an inhibitor of CYP2D6 and hERG channel (IC50s: 5.4 and 0.8 μM).

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.

Diphenylpyraline hydrochloride (4-Diphenylmethoxy-1-methylpiperidine hydrochloride) is used in the treatment of Parkinsonism.It is a first-generation antihistamine with anticholinergic effects, functions as a dopamine reuptake inhibitor.

Brompheniramine ((±)-Brompheniramine) is a potent and orally active alkylamine class antihistamine. Brompheniramine is a selective antagonist of histamine H1 receptor (Kd = 6.06 nM). Brompheniramine can be used in the research of allergic rhinitis that has anticholinergic, antidepressant and anesthetic properties. Brompheniramine can block the calcium channels, sodium channels, and hERG channels with IC 50 s of 16.12 μM, 21.26 μM, and 0.90 μM, respectively [1] [2] [3] [4].

Phenyltoloxamine (Bistrimin) is an antihistamine agent with sedative and analgesic effects. Phenyltoloxamine also has potent Sigma-1 receptor binding affinity with Ki of 160 nM [1] [2] [3].

Oxomemazine is a phenothiazine-based histamine H1-receptor blocker with pronounced antimuscarinic activity. Oxomemazine is a selective antagonist of mycotoxins M1 receptors, showing high (Ki=84 nM, M1 receptors) and low (Ki=1.65 μM, M2 receptors) affinity sites 20 times the difference[1]. Oxomemazine is an antihistamine and anticholinergic agent used in studies related to cough studies[2].

Cetirizine methyl ester, an impurity of Cetirizine, serves as a specific, orally active, and long-acting histamine H1-receptor antagonist. As a second-generation antihistamine and the carboxylated metabolite of hydroxyzine, Cetirizine effectively counters allergic reactions [1].

Cetirizine Impurity C dihydrochloride, a specific impurity of Cetirizine, is associated with a second-generation antihistamine that serves as the carboxylated metabolite of hydroxyzine. This compound acts as a specific, orally active, and long-acting antagonist of the histamine H1-receptor [1] [2].

Dexbrompheniramine, an orally active H1 receptor antagonist (antihistamine), mitigates the impacts of the natural chemical histamine in the body. It is utilized in the study of hay fever and urticaria [1].

Bromodiphenhydramine (Ambodryl) has antimicrobial activities which can be used in the cutaneous allergies research. Bromodiphenhydramine is an effective antihistamine that can inhibit a large number of Gram-negative and Gram-positive bacteria [1] [2] [3].

Epinastine (WAL801), a potent, selective, and orally-active antihistamine and mast cell stabilizer, functions as a histamine H1 receptor antagonist. It also inhibits IL-8 release from human eosinophils, showcasing antiallergic action [1] [2] [3] [4].

Propiomazine is an orally active antihistamine agent that possesses sedative properties. It finds utility in insomnia research [1] [2].

Phenindamine (Nu 1504) is an H1-receptor antagonist which is antihistamine[1].

Cetirizine Impurity C is an impurity of Cetirizine. Cetirizine is a second-generation antihistamine and the carboxylated metabolite of hydroxyzine. It acts as a specific, orally active, and long-acting antagonist of the histamine H1-receptor[1][2].

Sequifenadine has the potential in researching of inflammatory eye disease with allergic symptoms that is a H1-antihistamine [1] [2].