H1 antagonists, also called H1 blockers, are a class of medications that block the action of histamine at the H1 receptor, helping to relieve allergic reactions. Agents where the main therapeutic effect is mediated by negative modulation of histamine receptors are termed antihistamines; other agents may have antihistaminergic action but are not true antihistamines.
Diphenhydramine (DPH) is an antihistamine and sedative mainly used to treat allergies, insomnia, and symptoms of the common cold. It is also less commonly used for tremors in parkinsonism, and nausea. It is taken by mouth, injected into a vein, injected into a muscle, or applied to the skin. Maximal effect is typically around two hours after a dose, and effects can last for up to seven hours.
Anticholinergics are substances that block the action of the acetylcholine (ACh) neurotransmitter at synapses in the central and peripheral nervous system.
Brompheniramine, sold under the brand name Dimetapp among others, is a first-generation antihistamine drug of the propylamine (alkylamine) class. It is indicated for the treatment of the symptoms of the common cold and allergic rhinitis, such as runny nose, itchy eyes, watery eyes, and sneezing. Like the other first-generation drugs of its class, it is considered a sedating antihistamine.
Benadryl is a brand of various antihistamine medications used to stop allergies, whose content varies in different countries, but which includes some combination of diphenhydramine, acrivastine, and/or cetirizine.
Dimenhydrinate, sold under the brand name Dramamine, among others, is an over-the-counter medication used to treat motion sickness and nausea. Dimenhydrinate is a theoclate salt composed of diphenhydramine and 8-chlorotheophylline in a 1:1 ratio.
Chlorphenamine, also known as chlorpheniramine, is an antihistamine used to treat the symptoms of allergic conditions such as allergic rhinitis. It is taken orally. The medication takes effect within two hours and lasts for about 4–6 hours. It is a first-generation antihistamine and works by blocking the H1 receptor.
Cetirizine is a second-generation antihistamine used to treat allergic rhinitis, dermatitis, and urticaria (hives). It is taken by mouth. Effects generally begin within thirty minutes and last for about a day. The degree of benefit is similar to other antihistamines such as diphenhydramine, which is a first-generation antihistamine.
Promethazine, sold under the brand name Phenergan among others, is a first-generation antihistamine, sedative, and antiemetic used to treat allergies, insomnia, and nausea. It may also help with some symptoms associated with the common cold and may also be used for sedating people who are agitated or anxious, an effect that has led to some recreational use. Promethazine is taken by mouth (oral), as a rectal suppository, or by injection into a muscle (IM).
Doxylamine is an antihistamine medication used to treat insomnia and allergies, and—in combination with pyridoxine (vitamin B6)—to treat morning sickness in pregnant women. It is available over-the-counter and is typically sold under such brand names as Equate, Unisom, or ZzzQuil, among others; and it is used in nighttime cold medicines (e.g., NyQuil) and pain medications containing acetaminophen and/or codeine to help with sleep. The medication is delivered chemically by the salt doxylamine succinate and is taken by mouth. Doxylamine and other first-generation antihistamines are the most widely used sleep medications in the world.Typical side effects of doxylamine (at recommended doses) include dizziness, drowsiness, grogginess, and dry mouth, among others.
Clemastine, also known as meclastin, is a first-generation H1 histamine antagonist (antihistamine) with anticholinergic properties (drying) and sedative side effects. Like all first-generation antihistamines, it is sedating.
Orphenadrine is an anticholinergic drug of the ethanolamine antihistamine class; it is closely related to diphenhydramine. It is a muscle relaxant that is used to treat muscle pain and to help with motor control in Parkinson's disease, but has largely been superseded by newer drugs. It is considered a dirty drug due to its multiple mechanisms of action in different pathways. It was discovered and developed in the 1940s.
Ketotifen is an antihistamine medication and a mast cell stabilizer used to treat allergic conditions such as conjunctivitis, asthma, and urticaria (hives). Ketotifen is available in ophthalmic and oral forms: the ophthalmic form relieves eye itchiness and irritation associated with seasonal allergies, while the oral form helps prevent systemic conditions such as asthma attacks and allergic reactions. In addition to treating allergies, ketotifen has shown efficacy in managing systemic mast cell diseases such as mastocytosis and mast cell activation syndrome (MCAS), which involve abnormal accumulation or activation of mast cells throughout the body. Ketotifen is also used for other allergic-type conditions like atopic dermatitis (eczema) and food allergies.
Chloropyramine is a classical first-generation antihistamine drug approved in Eastern European countries for the treatment of allergic conjunctivitis, allergic rhinitis, bronchial asthma, and other atopic (allergic) conditions. Related indications for clinical use include angioedema, allergic reactions to insect bites, food and drug allergies, and anaphylactic shock.
Sominex is the trademarked name for several over the counter sleep aids.
Oxybutynin, sold under the brand name Ditropan among others, is an anticholinergic medication primarily used to treat overactive bladder. It is widely considered a first-line therapy for overactive bladder due to its well-studied side effect profile, broad applicability, and continued efficacy over long periods of time. It works similar to tolterodine, darifenacin, and solifenacin, although it is usually preferred over these medications. It is sometimes used off-label for treatment of hyperhidrosis, or excessive sweating. It has also been used off-label to treat bed wetting in children, but this use has declined, as it is most likely ineffective in this role. It is taken by mouth or applied to the skin.
Carbinoxamine is an antihistamine and anticholinergic agent. It is used for hay fever, vasomotor rhinitis, mild urticaria, angioedema, dermatographism and allergic conjunctivitis. Carbinoxamine is a histamine antagonist, specifically an H1-antagonist. The maleic acid salt of the levorotatory isomer is sold as the prescription drug rotoxamine.
Antihistamines are drugs which treat allergic rhinitis, common cold, influenza, and other allergies. Typically, people take antihistamines as an inexpensive, generic drug that can be bought without a prescription and provides relief from nasal congestion, sneezing, or hives caused by pollen, dust mites, or animal allergy with few side effects. Antihistamines are usually for short-term treatment. Chronic allergies increase the risk of health problems which antihistamines might not treat, including asthma, sinusitis, and lower respiratory tract infection. Consultation of a medical professional is recommended for those who intend to take antihistamines for longer-term use.
Antazoline is a 1st generation antihistamine with anticholinergic properties used to relieve nasal congestion and in eye drops, usually in combination with naphazoline, to relieve the symptoms of allergic conjunctivitis. To treat allergic conjunctivitis, antazoline can be combined in a solution with tetryzoline. The drug is a Histamine H1 receptor antagonist: selectively binding to but not activating the receptor, thereby blocking the actions of endogenous histamine and subsequently leading to the temporary relief of the negative symptoms brought on by histamine.
Phenbenzamine, sold under the brand name Antergan and known by the former developmental code name RP-2339, is an antihistamine of the ethylenediamine class which also has anticholinergic properties. It was introduced in 1941 or 1942 and was the first antihistamine to be introduced for medical use. Soon following its introduction, phenbenzamine was replaced by another antihistamine of the same class known as mepyramine. Following this, other antihistamines, such as diphenhydramine, promethazine, and tripelennamine, were developed and introduced. Owing to their sedative effects, phenbenzamine and promethazine were assessed in the treatment of manic depression in France in the 1940s and were regarded as promising therapies for such purposes. Whereas phenbenzamine was the first clinically useful antihistamine, piperoxan was the first compound with antihistamine properties to be discovered and was synthesized in the early 1930s.
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