Alcaftadine is a broad-spectrum antihistamine displaying a high affinity for histamine H1 and H2 receptors and a lower affinity for H4 receptors. It also exhibits modulatory action on immune cell recruitment and mast cell stabilizing effects. Alcaftadine is an inhibitor of the release of histamine from mast cells. Decreased chemotaxis and inhibition of eosinophil activation has also been demonstrated. LASTACAFT® (alcaftadine ophthalmic solution) indicated for the prevention of itching associated with allergic conjunctivitis.

Epinastine (brand names Alesion, Elestat, Purivist, Relestat) is a second-generation antihistamine and mast cell stabilizer. Epinastine is a topically active, direct H1-receptor antagonist and an inhibitor of the release of histamine from the mast cell. Epinastine is selective for the histamine H1-receptor and has affinity for the histamine H2 receptor. Epinastine also possesses affinity for the α1-, α2-, and 5-HT2 –receptors. Epinastine does not penetrate the blood/brain barrier and, therefore, is not expected to induce side effects of the central nervous system. Elestat ophthalmic solution is indicated for the prevention of itching associated with allergic conjunctivitis.

Ketotifen is a cycloheptathiophene blocker of histamine H1 receptors and release of inflammatory mediators. It has been proposed for the treatment of asthma, rhinitis, skin allergies, and anaphylaxis. Ketotifen was developed in 1970 by Sandoz Pharmaceuticals of Switzerland. It is a benzocycloheptathiophene derivative and was initially marketed as an inhibitor of anaphylaxis. The pharmacodynamic properties of ketotifen are many, because it is an inhibitor of the release and/or activity of mast cell and basophil mediators, including histamine, neutrophil, and eosinophil chemotactic factors, arachidonic acid metabolites, prostaglandins, and leukotrienes. Properties of ketotifen which may contribute to its antiallergic activity and its ability to affect the underlying pathology of asthma include inhibition of the development of airway hyper-reactivity associated with activation of platelets by PAF (Platelet Activating Factor), inhibition of PAF-induced accumulation of eosinophils and platelets in the airways, suppression of the priming of eosinophils by human recombinant cytokines and antagonism of bronchoconstriction due to leukotrienes. Ketotifen is marketed under many brand names worldwide. Ketotifen inhibits the release of mediators from mast cells involved in hypersensitivity reactions. Decreased chemotaxis and activation of eosinophils have also been demonstrated. Ketotifen also inhibits cAMP phosphodiesterase.

Azelastine, a phthalazine derivative, is an antihistamine and mast cell stabilizer. Azelastine is oxidatively metabolized to the principal active metabolite, desmethylazelastine, by the cytochrome P450 enzyme system. It is indicated for the relief of the symptoms of seasonal allergic rhinitis and perennial allergic rhinitis. The most common adverse reactions are: pyrexia, dysgeusia, nasal discomfort, epistaxis, headache, sneezing, fatigue, somnolence, upper respiratory infection, cough, rhinalgia, vomiting, otitis media, contact dermatitis, and oropharyngeal pain. Concurrent use of Azelastine with alcohol or other central nervous system depressants should be avoided because reductions in alertness and impairment of central nervous system performance may occur.

Olopatadine is an antihistamine (as well as anticholinergic and mast cell stabilizer) used to treat itching associated with allergic conjunctivitis (eye allergies). Olopatadine is a selective histamine H1 antagonist that 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. Olopatadine is devoid of effects on alpha-adrenergic, dopamine and muscarinic type 1 and 2 receptors. Some known side effects include a headache (7% of occurrence), eye burning and/or stinging (5%), blurred vision, dry eyes, foreign body sensation, hyperemia, keratitis, eyelid edema, pruritus, asthenia, sore throat (pharyngitis), rhinitis, sinusitis, and taste perversion.

Lodoxamide is a mast-cell stabilizer for topical administration into the eye. This compound belongs to the class of organic compounds known as alpha amino acids and derivatives. Lodoxamide inhibits the in vivo Type I immediate hypersensitivity reaction. In vitro, Lodoxamide stabilizes mast cells and prevents antigen-stimulated release of histamine. In addition, Lodoxamide prevents the release of other mast cell inflammatory mediators and inhibits eosinophil chemotaxis. Although Lodoxamide's precise mechanism of action is unknown, the drug has been reported to prevent calcium influx into mast cells upon antigen stimulation. Among side effects to Lodoxamide, the most frequently reported ocular adverse experiences were transient burning, stinging, or discomfort upon instillation. Nonocular events reported were headache and heat sensation, dizziness, somnolence, nausea, stomach discomfort, sneezing, dry nose, and rash.

Cromolyn is a mast cell stabilizer. In vitro and in vivo animal studies have shown that cromolyn sodium inhibits the degranulation of sensitized mast cells, which occurs after exposure to specific antigens. Cromolyn sodium acts by inhibiting the release of histamine and SRS-A (slow-reacting substance of anaphylaxis) from the mast cell. Cromolyn is indicated in the management of patients with mastocytosis, prophylaxis (long-term control) of bronchial asthma, prevention of exercise-induced bronchospasm, prevention and treatment of seasonal and perennial allergic rhinitis The most frequently reported adverse reactions attributed to cromolyn sodium treatment were: throat irritation or dryness, bad taste, cough, wheeze, nausea.

Oxymetazoline is an adrenergic alpha-agonist, direct acting sympathomimetic, used as a vasoconstrictor to relieve nasal congestion The sympathomimetic action of oxymetazoline constricts the smaller arterioles of the nasal passages, producing a prolonged (up to 12 hours), gentle and decongesting effect. Oxymetazoline elicits relief of conjunctival hyperemia by causing vasoconstriction of superficial conjunctival blood vessels. The drug's action has been demonstrated in acute allergic conjunctivitis and in chemical (chloride) conjunctivitis. Oxymetazoline is self-medication for temporary relief of nasal congestion associated with the common cold, hay fever, or other upper respiratory allergies. Oxymetazoline is available over-the-counter as a topical decongestant in the form of oxymetazoline hydrochloride in nasal sprays such as Afrin, Operil, Dristan, Dimetapp, oxyspray, Facimin, Nasivin, Nostrilla, Sudafed OM, Vicks Sinex, Zicam, SinuFrin, and Mucinex Full Force. Due to its vasoconstricting properties, oxymetazoline is also used to treat nose bleeds and eye redness.

Xylometazoline, also spelled xylomethazoline, is a medication which is used to improve symptoms of nasal congestion, allergic rhinitis, and sinusitis. Xylometazoline was patented in 1956 and came into medical use in 1959. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. The drug works by stimulating adrenergic receptors on the lamina propria of blood vessels in the nose. The decongestant effect is due to constriction of large veins in the nose which swell up during the inflammation of any infection or allergy of the nose. The smaller arteries are also constricted and this causes the colour of the nasal epithelium to be visibly paler after dosage. The standard adult solution strength is 0.1% w/v xylometazoline (or 1 mg per 1 mL solution), and the dose for children under 12 is usually 0.05% (0.5 mg/mL).

Tetrahydrozoline is an alpha adrenergic receptor agonist, which is used in form of nasal solution or spray (Tyzin) for decongestion of nasal and nasopharyngeal mucosa.