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.

Desloratadine is an active, descarboethoxy metabolite of loratadine. It acts by selective inhibition of H1 histamine receptor and thus provides relief to patients with allergic rhinitis and chronic idiopathic urticaria. Desloratadine was approved by FDA and it is currently marketed under the name Clarinex (among the others).

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.

Fexofenadine is a second-generation, long lasting H1-receptor antagonist (antihistamine) which has a selective and peripheral H1-antagonist action. Histamine is a chemical that causes many of the signs that are part of allergic reactions, such as the swelling of tissues. Histamine is released from histamine-storing cells (mast cells) and attaches to other cells that have receptors for histamine. The attachment of the histamine to the receptors causes the cell to be "activated," releasing other chemicals which produce the effects that we associate with allergy. Fexofenadine blocks one type of receptor for histamine (the H1 receptor) and thus prevents activation of cells by histamine. Unlike most other antihistamines, Fexofenadine does not enter the brain from the blood and, therefore, does not cause drowsiness. Fexofenadine lacks the cardiotoxic potential of terfenadine, since it does not block the potassium channel involved in repolarization of cardiac cells. Fexofenadine is sold under the trade name Allegra among others. ALLEGRA is indicated for the relief of symptoms associated with seasonal allergic rhinitis in adults and children 2 years of age and older.

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.

Levocetirizine dihydrochloride is the R enantiomer of cetirizine hydrochloride, a racemic compound with antihistaminic properties. Levocetirizine is a third-generation non-sedative antihistamine indicated for the relief of symptoms associated with seasonal and perennial allergic rhinitis and uncomplicated skin manifestations of chronic idiopathic urticaria. It was developed from the second-generation antihistamine cetirizine. Levocetirizine was approved by the United States Food and Drug Administration on May 25, 2007 and is marketed under the brand XYZAL. Its principal effects are mediated via selective inhibition of H1 receptors. The antihistaminic activity of levocetirizine has been documented in a variety of animal and human models. In vitro binding studies revealed that levocetirizine has an affinity for the human H1-receptor 2-fold higher than that of cetirizine (Ki = 3 nmol/L vs. 6 nmol/L, respectively). The clinical relevance of this finding is unknown.

Loratadine is a derivative of azatadine and a second-generation histamine H1 receptor antagonist used in the treatment of allergic rhinitis and urticaria. Unlike most classical antihistamines (histamine H1 antagonists) it lacks central nervous system depressing effects such as drowsiness. Loratadine competes with free histamine and exhibits specific, selective peripheral H1 antagonistic activity. This blocks the action of endogenous histamine, which subsequently leads to temporary relief of the negative symptoms (eg. nasal congestion, watery eyes) brought on by histamine. Loratadine has low affinity for cholinergic receptors and does not exhibit any appreciable alpha-adrenergic blocking activity in-vitro. Loratadine also appears to suppress the release of histamine and leukotrienes from animal mast cells, and the release of leukotrienes from human lung fragments, although the clinical importance of this is unknown.

Cetirizine, a human metabolite of hydroxyzine, is an antihistamine; its principal effects are mediated via selective inhibition of peripheral H1 receptors. It is indicated for the relief of nasal and non-nasal symptoms associated with seasonal or perennial allergic rhinitis, hay fever and chronic idiopathic urticaria. Commonly reported adverse reactions of cetirizine include headache, dry mouth and drowsiness or fatigue. Pharmacokinetic interaction studies with Cetirizine in adults were conducted with pseudoephedrine, antipyrine, ketoconazole, erythromycin and azithromycin. No interactions were observed.

Clemastine is an antihistamine with anticholinergic (drying) and sedative side effects. Clemastine is a selective histamine H1 antagonist and 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. It is used for the relief of symptoms associated with allergic rhinitis such as sneezing, rhinorrhea, pruritus and acrimation. Also for the management of mild, uncomplicated allergic skin manifestations of urticaria and angioedema. Used as self-medication for temporary relief of symptoms associated with the common cold.

Trimethobenzamide (trade names Tebamide, Tigan) is an antiemetic used to prevent nausea and vomiting. Trimethobenzamide is an antagonist of the D2 receptor, that affects the chemoreceptor trigger zone (CTZ) of the medulla oblongata to suppress nausea and vomiting. The oral bioavailability of trimethobenzamide is 60% to 100%. The time to peak is about 45 minutes after oral administration and; I.M. about 30 minutes after intramuscular administration. The onset action of trimethobenzamide for antiemetic effects is 10-40 minutes after oral administration and; 15-35 minutes after intramuscular administration. The duration of action is 3-4 hours. Trimethobenzamide is generally considered the most potent antiemetic that does not have effects on the serotonergic, dopaminergic, or histaminergic systems, so it has a lower likelihood of causing undesired side effects. Possible side effects include drowsiness, dizziness, headache, diarrhea, muscle cramps, and blurred vision. More serious adverse effects include skin rash, tremors, parkinsonism, and jaundice.