DEXBROMPHENIRAMINE is an alkylamine derivative with anticholinergic and sedative properties. It is a histamine H1-receptor antagonist that competes with histamine for the H1-receptor sites on effector cells in the gastrointestinal tract, blood vessels, and respiratory tract. The antagonistic action of this agent blocks the activities of endogenous histamine, which subsequently leads to temporary relief from the negative histamine-mediated symptoms of an allergic reaction such as bronchoconstriction, vasodilation, increased capillary permeability and spasmodic contractions of the gastrointestinal smooth muscle. DEXBROMPHENIRAMINE as a part of combination medicine is used to treat symptoms of the common cold or seasonal allergies, including sneezing, runny or stuffy nose, and itchy, watery eyes.

Triprolidine is a first generation histamine H1 antagonist, which in combination with codeine phosphate and pseudoephedrine hydrochloride is sold under brand name TRIACIN-C. TRIACIN-C is indicated for temporary relief of coughs and upper respiratory symptoms, including nasal congestion, associated with allergy or the common cold.

Dexchlorpheniramine, the d-isomer of the racemic compound chlorpheniramine, is two times more active than chlorpheniramine. Dexchlorpheniramine does not prevent the release of histamine, but rather, competes with free histamine for binding at the H1-receptor sites, and competitively antagonizes the effects of histamine on H1-receptors in the GI tract, uterus, large blood vessels, and bronchial muscle. Blockade of H1-receptors also suppresses the formation of oedema, flare, and pruritus that result from histaminic activity. Since dexchlorpheniramine binds to central and peripheral H1-receptors, sedative effects are likely to occur. H1-antagonists are structurally similar to anticholinergic agents and therefore possess the potential to exhibit anticholinergic properties of varying degrees. They also have antipruritic effects. Dexchlorpheniramine has high antihistaminic activity, moderate anticholinergic effects and minimal sedative effects. The drug does not possess antiemetic properties.

Brompheniramine is an antihistaminergic medication of the propylamine class. It is a first-generation antihistamine, which is used for the treatment of the symptoms of the common cold and allergic rhinitis, such as runny nose, itchy eyes, watery eyes, and sneezing. In allergic reactions, an allergen interacts with and cross-links surface IgE antibodies on mast cells and basophils. Once the mast cell-antibody-antigen complex is formed, a complex series of events occurs that eventually leads to cell-degranulation and the release of histamine (and other chemical mediators) from the mast cell or basophil. Once released, histamine can react with local or widespread tissues through histamine receptors. Brompheniramine is a histamine H1 antagonist of the alkylamine class. It provides effective, temporary relief of sneezing, watery and itchy eyes, and runny nose due to hay fever and other upper respiratory allergies. Brompheniramine is metabolised by cytochrome P450s. The halogenated alkylamine antihistamines all exhibit optic isomerism and brompheniramine products contain racemic brompheniramine maleate whereas dexbrompheniramine (Drixoral) is the dextrorotary (right-handed) stereoisomer.

Cyclizine (cyclizine hydrochloride, Valoid®) is a histamine H1 antagonist of the piperazine class which is characterised by a low incidence of drowsiness. It possesses anticholinergic and antiemetic properties. The exact mechanism by which cyclizin (cyclizine hydrochloride, Valoid®) can prevent or suppress both nausea and vomiting from various causes is unknown. It increases lower oesophageal sphincter tone and reduces the sensitivity of the labyrinthine apparatus. It may inhibit the part of the midbrain known collectively as the emetic centre.

Chlorpheniramine is an antihistamine. Chlorpheniramine binds to the histamine H1 receptor. This blocks the action of endogenous histamine, which subsequently leads to temporary relief of the negative symptoms brought on by histamine. Chlorpheniramine is used for relieving symptoms of sinus congestion, sinus pressure, runny nose, watery eyes, itching of the nose and throat, and sneezing due to upper respiratory infections (eg, colds), allergies, and hay fever. In addition to being a histamine H1 receptor (HRH1) antagonist, chlorphenamine has been shown to work as a serotonin-norepinephrine reuptake inhibitor or SNRI.

Chlorcyclizine is a first generation phenylpiperazine class antihistamine used to treat urticaria, rhinitis, pruritus, and other allergy symptoms. Chlorcyclizine also has some local anesthetic, anticholinergic, and antiserotonergic properties, and can be used as an antiemetic. Chlorcyclizine temporarily relieves the symptoms due to hay fever or other upper respiratory allergies. It has also being shown to possess in vitro and in vivo activity against hepatitis C virus.

Thonzylamine (also known as neohetramine) is an antihistamine and anticholinergic drug, which is used in combination with others compounds for the temporarily relieves symptoms due to the common cold: hay fever (allergic rhinitis) or other upper respiratory allergies: nasal congestion; runny nose and so on. In addition, thonzylamine was investigated for the treatment of tuberculosis, when this drug caused a slight reduction in the extent of tuberculosis in experimentally infected guinea pigs and caused a slight but significant increase in the length of survival.

Pheniramine is an antihistamine used to treat allergic conditions such as hay fever or urticaria. It is generally sold in combination with other medications, rather than as a stand-alone drug. Allergies are caused by an excessive type 1 hypersensitivity response of the body to allergens, mediated by inappropriate histamine signalling. By inhibiting the binding of histamine, antihistamines decrease the normal histamine response from cells, consequently decreasing allergic symptoms. Antihistamines such as pheniramine appear to compete with histamine for histamine H1- receptor sites on effector cells. The antihistamines antagonize those pharmacological effects of histamine which are mediated through activation of H1- receptor sites and thereby reduce the intensity of allergic reactions and tissue injury response involving histamine release. Antihistamines suppress the histamine-induced wheal (swelling) and flare (vasodilation) response by blocking the binding of histamine to its receptors on nerves, vascular smooth muscle, glandular cells, endothelium, and mast cells. They effectively exert competitive antagonism of histamine for H1-receptors. Pheniramine is marketed under the trade name Avil and Visine-A among others).

Pyrilamine (also known as Mepyramine) is a first generation antihistamine, targeting the H1 receptor. However, it rapidly permeates the brain and so often causes drowsiness as a side effect. It is used in over-the-counter combination products for colds and menstrual symptoms. Mepyramine is a histamine H1 receptor inverse agonist. It binds to a G protein-coupled form of the receptor and promotes a G protein-coupled inactive state of the H1 receptor that interferes with the Gq/11-mediated signaling. Mepyramine competes with histamine for binding at H1-receptor sites on the effector cell surface, resulting in suppression of histaminic edema, flare, and pruritus. The sedative properties of Mepyramine occur at the subcortical level of the CNS. It has mild hypnotic properties and some local anesthetic action and is used for allergies (including skin eruptions) both parenterally and locally. It is a common ingredient of cold remedies.