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.

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).

Acrivastine is a triprolidine analog antihistamine indicated for the treatment of allergies and hay fever. As an H1 receptor antagonist, it functions by blocking the action of histamine at this receptor thereby preventing the symptoms associated with histamine release such as pruritis, vasodilation, hypotension, edema, bronchoconstriction, and tachycardia. Acrivastine is currently available in combination with pseudoephedrine as the FDA-approved product Semprex-D. It’s used for the relief of symptoms associated with seasonal allergic rhinitis such as sneezing, rhinorrhea, pruritus, lacrimation, and nasal congestion. Acrivastine, a structural analog of triprolidine hydrochloride, exhibits H1-antihistaminic activity in isolated tissues, animals, and humans, and has sedative effects in humans. The propionic acid derivative of acrivastine is a metabolite in several animal species (as well as in man) and also exhibits H1-antihistaminic activity.

Terfenadine under brand name Seldane was used for the treatment of allergic rhinitis and allergic skin disorders but was withdrawn because of the serious side effect, heart rhythm problems. Terfenadine is a potent antagonist of histamine H1-receptor-mediated responses.

Phenyltoloxamine is an ethanolamine derivative with antihistaminic property, which is used in combination with some analgesics for the temporary relief of minor aches and pains associated with headache; backache; muscular aches; temporarily reduces fever and some others disorders. Phenyltoloxamine blocks H1 histamine receptor, thereby inhibiting phospholipase A2 and production of endothelium-derived relaxing factor, nitric oxide. Subsequent lack of activation of guanylyl cyclase through nitric oxide results in decreased cyclic GMP levels, thereby inhibiting smooth muscle constriction of various tissues, decreasing capillary permeability and decreasing other histamine-activated allergic reactions.

Caramiphen is a muscarinic M1 acetylcholine receptor antagonist, which was used for the treatment of Parkinson Disease and cough, but then there using were discontinued. Caramiphen is also used in local anesthesia, and effect could be achieved through the suppression of voltage-gated Na⁺ currents.

Bromhexine is used for conditions where there are a lot of thick mucus in the airways. Bromhexine acts on the mucus at the formative stages in the glands, within the mucus-secreting cells. Bromhexine disrupts the structure of acid mucopolysaccharide fibres in mucoid sputum and produces a less viscous mucus, which is easier to expectorate. In addition, bromhexine has antioxidant properties. Occasional, mild side effects include: a feeling of fullness in the stomach (bloatedness), diarrhea, dizziness, headache, indigestion, nausea, sweating and skin rashes. Bromhexine may increase the concentration of concurrently administered antibiotics in bronchial secretions. No clinically relevant interactions with other medications have been reported.