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.

Levocabastine (trade name Livo) is a selective second-generation H1-receptor antagonist used for allergic conjunctivitis. Levocabastine binds the G protein-coupled neurotensin receptor 2 (NTR2), but not NTR1, where it behaves as a weak partial inverse agonist. In an environmental study, LIVOSTIN 0.05% (levocabastine hydrochloride ophthalmic suspension) instilled four times daily was shown to be significantly more effective than its vehicle in reducing ocular itching associated with seasonal allergic conjunctivitis. After instillation in the eye, levocabastine is systemically absorbed. However, the amount of systemically absorbed levocabastine after therapeutic ocular doses is low (mean plasma concentrations in the range of 1-2 ng/mL). Brand name Livostin is no longer available in the U.S., but generic versions may still be available. Common side effects include burning, stinging, itching, or watering of the eyes, eye irritation or discomfort, blurred vision, dry or puffy eyes, headache, nosebleed, nausea, or fatigue.

Nedocromil is a medication considered as mast cell stabilizer used to treat itching associated with allergic conjunctivitis. Nedocromil has been shown to inhibit the in vitro activation of, and mediator release from, a variety of inflammatory cell types associated with asthma, including eosinophils, neutrophils, macrophages, mast cells, monocytes, and platelets. Nedocromil inhibits activation and release of inflammatory mediators such as histamine, prostaglandin D2 and leukotrienes c4 from different types of cells in the lumen and mucosa of the bronchial tree. These mediators are derived from arachidonic acid metabolism through the lipoxygenase and cyclo-oxygenase pathways. The mechanism of action of nedocromil may be due partly to inhibition of axon reflexes and release of sensory neuropeptides, such as substance P, neurokinin A, and calcitonin-geneñrelated peptides. The result is inhibition of bradykinin-induced bronchoconstriction. Nedocromil does not possess any bronchodilator, antihistamine, or corticosteroid activity. Nedocromil is indicated for the treatment of itching associated with allergic conjunctivitis.

Astemizole is antihistamine drug, discovered by Janssen Pharmaceutical and used to prevent sneezing, runny nose, itching and watering of the eyes, and other allergic symptoms. The drug was withdrawn from U.S. market in 1999 due to the potential to cause arrhythmias at high doses.

Methylparaben (E number E218) is preservative in the food, cosmetic, and pharmaceutical industries. It is completely absorbed through the skin or after ingestion and and it is hydrolyzed to para-hydroxybenzoic acid, and metabolites are rapidly excreted in the urine. Methylparaben is on the FDA generally regarded as safe list.

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.

Azatadine is an antihistamine, which blocks the effects of the naturally occurring chemical histamine in the body. Azatadine is used to treat sneezing; runny nose; itching, watery eyes; hives; rashes; and other symptoms of allergies and the common cold. 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.

Chlorphenesin carbamate (Maolate, Musil) is a centrally acting muscle relaxant used to treat muscle pain and spasms. Сhlorphenesin acts in the central nervous system (CNS) rather than directly on skeletal muscle. It also has antifungal and some antibacterial properties. The major adverse effects are drowsiness and dizziness.

Rotoxamine ((S)-carbinoxamine) is maleic acid salt of the levorotatory isomer of Carbinoxamine (a first-generation antihistamine of the ethanolamine class). Ethanolamine antihistamines have significant antimuscarinic activity and produce marked sedation in most patients. In addition to the usual allergic symptoms, the drug also treats an irritant cough and nausea, vomiting, and vertigo associated with motion sickness. It also is used commonly to treat drug-induced extrapyramidal symptoms as well as to treat mild cases of Parkinson's disease. Rotoxamine is used to treat runny or stuffy nose, sneezing, itching, watery eyes, hives, skin rash, itching, and other symptoms of allergies and the common cold.

Dimetindene (trade name Fenistil; other name dimethindene maleate) is a potent antipruritic antihistamine, characterized by the small size of its effective dose and its rapidity of action. Dimetindene is an antihistamine/anticholinergic that is a selective H1 antagonist. Its effect sets in after 20 to 60 minutes and lasts several hours. Dimetindene drops as well as Dimetindene syrup is particularly indicated in pediatric practice. Dimetindene is indicated as symptomatic treatment of allergic reactions: urticaria, allergies of the upper respiratory tract such as hay fever and perennial rhinitis, food, and drug allergies; pruritus of various origins, except pruritus due to cholestasis; insect bites. Dimetindene is also indicated for pruritus in eruptive skin diseases such as chicken-pox. Dimetindene can be as an adjuvant in eczema and other pruriginous dermatoses of allergic origin.