What does antihistamine treat?
Antihistamine
H-antihistamines are among first-line therapy to treat gastrointestinal conditions including peptic ulcers and gastroesophageal reflux disease. Some formulations are available over the counter. Most side effects are due to cross-reactivity with unintended receptors. Cimetidine, for example, is notorious for antagonizing androgenic testosterone and DHT receptors at high doses.
Clemastine
Clemastine is rapidly absorbed from the gastrointestinal tract and peak plasma concentrations are attained in 2–4 hours. Antihistamines are thought to be metabolized in the liver, mostly by mono-/didemethylation and glucuronide conjugation. It is an inhibitor of cytochrome P450 CYP2D6 and may interfere with other drugs metabolized by this isozyme.
Antihistamine
Examples:
Antazoline
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.
Triprolidine
Triprolidine is an over-the-counter antihistamine with anticholinergic properties. It is used to combat the symptoms associated with allergies and is sometimes combined with other cold medications designed to provide general relief for flu-like symptoms. Like many antihistamines, the most common side effect is drowsiness.
H1 antagonist
H-antihistamines are clinically used in the treatment of histamine-mediated allergic conditions. These indications may include:H-antihistamines can be administered topically (through the skin, nose, or eyes) or systemically, based on the nature of the allergic condition.
H1 antagonist
H antagonists, also called H blockers, are a class of medications that block the action of histamine at the H 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.
Cidoxepin
Cidoxepin has recently been reinvestigated and is now currently under development as an antihistamine by Elorac, Inc. for the treatment of chronic urticaria (hives). As of 2017, it is in phase II clinical trials for this indication. The drug was also under investigation for the treatment of allergic rhinitis (hay fever), atopic dermatitis (atopic eczema), and contact dermatitis, but development for these indications was discontinued.
Antihistamine
Histamine receptors exhibit constitutive activity, so antihistamines can function as either a neutral receptor antagonist or an inverse agonist at histamine receptors. Only a few currently marketed H-antihistamines are known to function as inverse agonists.
Triple response of Lewis
Histamine, or 2-(imidazol-4-yl)ethanamine, is a dibasic vasoactive amine that is located in most body tissues but is highly concentrated in the lungs, skin, and gastrointestinal tract. Histamine is derived from the decarboxylation of the aminoacid histidine, a reaction catalyzed by the enzyme L-histidine decarboxylase. Histamine is a small molecule, stored in granules of mast cells and basophils.
Daniel Bovet
Daniel Bovet (23 March 1907 – 8 April 1992) was a Swiss-born Italian pharmacologist who won the 1957 Nobel Prize in Physiology or Medicine for his discovery of drugs that block the actions of specific neurotransmitters. He is best known for his discovery in 1937 of antihistamines, which block the neurotransmitter histamine and are used in allergy medication. His other research included work on chemotherapy, sulfa drugs, the sympathetic nervous system, the pharmacology of curare, and other neuropharmacological interests.
Antihistamine
A combination of these effects, and in some cases metabolic ones as well, lead to most first-generation antihistamines having analgesic-sparing (potentiating) effects on opioid analgesics and to some extent with non-opioid ones as well. The most commonly used for the purpose include hydroxyzine, promethazine (enzyme induction especially helps with codeine and similar prodrug opioids), phenyltoloxamine, orphenadrine, and tripelennamine; some may also have intrinsic analgesic properties of their own, orphenadrine being an example.
Betamethasone/dexchlorpheniramine
Betamethasone/dexchlorpheniramine (trade names Betadexin, Celestamine) is a drug containing betamethasone and dexchlorpheniramine maleate to treat allergic conditions. Betamethasone is a steroid to relief itches and inflammation while dexchlorpheniramine maleate is an antihistamine to treat urticaria.
Mosquito bite allergy
Treatment of ordinary small or large mosquito bite reactions is limited to the use of non-sedative H1 antihistamines, e.g. cetirizine
or a drug with combined activity in inhibiting histamine and platelet-activating factor, e.g. rupatadine. Randomized, double-blinded, placebo-controlled studies are needed to determine if antileukotriene drugs or topical steroids have beneficial effects in reducing the symptoms of these bites.
Dutasteride
Although no reports specific to dutasteride currently exist, 5α-reductase inhibitors like finasteride have been found to be effective in the treatment of hirsutism (excessive facial and/or body hair growth) in women. In a study of 89 women with hyperandrogenism due to persistent adrenarche syndrome, finasteride produced a 93% reduction in facial hirsutism and a 73% reduction in bodily hirsutism after 2 years of treatment. Other studies using finasteride for hirsutism have also found it to be clearly effective. Dutasteride may be more effective than finasteride for this indication due to the fact that its inhibition of the 5α-reductase enzyme is comparatively more complete.
Antihistamine
Histamine produces increased vascular permeability, causing fluid to escape from capillaries into tissues, which leads to the classic symptoms of an allergic reaction — a runny nose and watery eyes. Histamine also promotes angiogenesis.
Histamine
Increased vascular permeability causes fluid to escape from capillaries into the tissues, which leads to the classic symptoms of an allergic reaction: a runny nose and watery eyes. Allergens can bind to IgE-loaded mast cells in the nasal cavity's mucous membranes. This can lead to three clinical responses:Histamine is a neurotransmitter that is released from histaminergic neurons which project out of the mammalian hypothalamus. The cell bodies of these neurons are located in a portion of the posterior hypothalamus known as the tuberomammillary nucleus (TMN). The histamine neurons in this region comprise the brain's histamine system, which projects widely throughout the brain and includes axonal projections to the cortex, medial forebrain bundle, and elsewhere. The histamine neurons in the TMN are involved in regulating the sleep-wake cycle and promote arousal when activated. The neural firing rate of histamine neurons in the TMN is strongly positively correlated with an individual's state of arousal. These neurons fire rapidly during periods of wakefulness, fire more slowly during periods of relaxation/tiredness, and stop firing altogether during REM and NREM (non-REM) sleep.
Mizolastine
Mizolastine (Mizollen) is a once-daily, non-sedating antihistamine. It blocks H receptors and is commonly fast-acting. It does not prevent the actual release of histamine from mast cells, it just prevents it binding to receptors. Side effects can include dry mouth and throat.
H1 antagonist
The first H-antihistamine discovered was piperoxan, by Ernest Fourneau and Daniel Bovet (1933) in their efforts to develop a guinea pig animal model for anaphylaxis at the Pasteur Institute in Paris. Bovet went on to win the 1957 Nobel Prize in Physiology or Medicine for his contribution. Following their discovery, the first-generation H-antihistamines were developed in the following decades. They can be classified on the basis of chemical structure, and agents within these groups have similar properties.
X = N, R1 = R2 = small alkyl groups
X = C
X = COSecond-generation H-antihistamines are newer drugs that are much more selective for peripheral H receptors as opposed to the central nervous system H receptors and cholinergic receptors. This selectivity significantly reduces the occurrence of adverse drug reactions, such as sedation, while still providing effective relief of allergic conditions.
The reason for their peripheral selectivity is that most of these compounds are zwitterionic at physiological pH (around pH 7.4). As such, they are very polar, meaning that they do not cross the blood–brain barrier and act mainly outside the central nervous system. However, some second-generation antihistamines, notably cetirizine, can interact with CNS psychoactive drugs such as bupropion and benzodiazepines.
Systemic:
Idiopathic hypersomnia
"Based on the role of histamine in keeping people awake (and hence the common side effect of anti-histamines such as diphenhydramine causing sleepiness), medications that act on histamine are under development for the treatment of excessive sleepiness." It remains to be seen whether these H3 antagonists (i.e., compounds such as pitolisant that promote the release of the wake-promoting amine histamine) will be particularly useful as wake-promoting agents in the treatment of idiopathic hypersomnia.
Histoplasma duboisii
Isolated lesions may be cleared by surgical removed, although some have been known to heal spontaneously. In contrast, deep lesions and disseminated disease require antifungal drug therapy. To date, no antifungal drug studies have specifically investigated the agent of African histoplasmosis. Hence most treatment approaches are based on the therapeutic strategies used to treat classical histoplasmosis caused by "H. capsulatum". Amphotericin B is a mainstay of antifungal treatment, with a recommended dose of 1 mg/kg/day, culminating in a minimum dose of 2 g. Clinical response is typically apparent after 2 weeks of intravenous administration. Ketoconazole is also effective, starting at 600–800 mg/day for 3 months followed by a reduced dose of 400 mg/day for a further 6 months. The organism is also thought to be susceptible to fluconazole in vivo. A multi-month course of Amphotericin B followed by itraconazole has been suggested for complicated infection in immunodeficient individuals. Milder forms of disease may respond to monotherapy with itraconazole. To ensure clearance of the agent, maintenance therapy of itraconazole at 200–400 mg/day until CD4+ counts remain stable for several months at a minimum of 150 cells/mm. Re-emergence of disease several years after apparent clearance has been reported, and on-going surveillance is warranted for this reason. Treatment for HIV positive individuals should run in parallel to highly active antiretroviral therapy (HAART). Even though HAART has greatly improved the prognosis of HIV disease, the risk of immune reconstitution inflammatory syndrome (IRIS) is known in patients with African histoplasmosis. No evidence of acquired antifungal drug resistance has been reported in "H. duboisii".
H1 antagonist
While H-antihistamines help against these effects, they work only if taken before contact with the allergen. In severe allergies, such as anaphylaxis or angioedema, these effects may be of life-threatening severity. Additional administration of epinephrine, often in the form of an autoinjector (Epi-pen), is required by people with such hypersensitivities.
Histamine
Metabolites of histamine are increased in the cerebrospinal fluid of people with schizophrenia, while the efficiency of H receptor binding sites is decreased. Many atypical antipsychotic medications have the effect of increasing histamine production, because histamine levels seem to be imbalanced in people with that disorder.
Immunotherapy
Immunotherapy is used to treat allergies. While allergy treatments (such as antihistamines or corticosteroids) treat allergic symptoms, immunotherapy can reduce sensitivity to allergens, lessening its severity.
Hydroxyzine
Hydroxyzine, sold under the brand names Atarax among others, is a medication of the antihistamine type. It is used in the treatment of itchiness, anxiety, and nausea, including that due to motion sickness. It is used either by mouth or injection into a muscle.
Common side effects include sleepiness, headache, and a dry mouth. Serious side effects may include QT prolongation. It is unclear if use during pregnancy or breastfeeding is safe. Hydroxyzine works by blocking the effects of histamine. It is in the piperazine family of chemicals.
It was first made by Union Chimique Belge in 1956 and was approved for sale by Pfizer in the United States later that year. In the United Kingdom 28 doses cost less than a pound. In the United States the wholesale cost in 2018 was about 0.05 USD per dose. In the United States about 8 million prescriptions were written for hydroxyzine in 2016.
Discovery and development of non-nucleoside reverse-transcriptase inhibitors
HIV drugs do not cure HIV infection, but the treatment aims at improving the quality of patients´ lives and decreased mortality.
25 antiretroviral drugs were available in 2009 for the treatment of HIV infection. The drugs belong to six different classes that act at different targets. The most popular target in the field of antiretroviral drug development is the HIV-1 reverse transcriptase (RT) enzyme. 
There are two classes of drugs that target the HIV-1 RT enzyme, nucleoside/nucleotide reverse-transcriptase inhibitors (NRTIs/NtRTIs) and non-nucleoside reverse-transcriptase inhibitors (NNRTIs). Drugs in these classes are important components of the HIV combination therapy called highly active antiretroviral therapy, better known as HAART.
Opioid
Itching tends not to be a severe problem when opioids are used for pain relief, but antihistamines are useful for counteracting itching when it occurs. Non-sedating antihistamines such as fexofenadine are often preferred as they avoid increasing opioid induced drowsiness. However, some sedating antihistamines such as orphenadrine can produce a synergistic pain relieving effect permitting smaller doses of opioids be used. Consequently, several opioid/antihistamine combination products have been marketed, such as "Meprozine" (meperidine/promethazine) and "Diconal" (dipipanone/cyclizine), and these may also reduce opioid induced nausea.
Brompheniramine
Brompheniramine (Bromfed, Dimetapp, Bromfenex, Dimetane, BPN, Lodrane), commonly marketed as its salt brompheniramine maleate, is an antihistamine drug of the propylamine (alkylamine) class. It is readily available over the counter and 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. It is a first-generation antihistamine and one of the drugs of highest anticholinergic activity.
Angioedema
In allergic angioedema, avoidance of the allergen and use of antihistamines may prevent future attacks. Cetirizine is a commonly prescribed antihistamine for angioedema. Some patients have reported success with the combination of a nightly low dose of cetirizine to moderate the frequency and severity of attacks, followed by a much higher dose when an attack does appear. Severe angioedema cases may require desensitization to the putative allergen, as mortality can occur. Chronic cases require steroid therapy, which generally leads to a good response. In cases where allergic attack is progressing towards airway obstruction, epinephrine may be life-saving.
Aquagenic pruritus
H1 and H2 blockers, such as loratadine, doxepin, or cimetidine, have historically been the first line of pharmacological treatment, but not all sufferers find relief with these medications. When antihistamines do work, loratadine seems to be the most effective for mild cases and doxepin most effective for more severe cases.
Cobicistat
Cobicistat, with trade name Tybost (formerly GS-9350) is a licensed drug for use in the treatment of human immunodeficiency virus infection (HIV/AIDS). Its major mechanism of action is through the inhibition of human CYP3A proteins.
Histamine dihydrochloride
It is also a FDA-approved active ingredient for topical analgesic use and is available in such products as GOLDEN CREME and Australian Dream Cream, which are used for the temporary relief of minor aches and pains of muscles and joints associated with arthritis, simple backache, bruises, sprains, and strains.
Histamine dihydrochloride is administered in conjunction with low doses of the immune-activating cytokine interleukin-2 (IL-2) in the post-remission phase of AML, i.e. when patients have completed the initial chemotherapy. This combination has been reported to significantly reduce the risk of relapse in AML. The effect is particularly pronounced in patients in their first remission who are below the age of 60.
Allergic rhinitis
Antihistamine drugs can be taken orally and nasally to control symptoms such as sneezing, rhinorrhea, itching, and conjunctivitis.
Hypnotic
In common use, the term "antihistamine" refers only to compounds that inhibit action at the H receptor (and not H, etc.).
Histamine
Histamine release occurs when allergens bind to mast-cell-bound IgE antibodies. Reduction of IgE overproduction may lower the likelihood of allergens finding sufficient free IgE to trigger a mast-cell-release of histamine.
Atazanavir
Atazanavir, sold under the trade name Reyataz among others, is an antiretroviral medication used to treat and prevent HIV/AIDS. It is generally recommended for use with other antiretrovirals. It may be used for prevention after a needlestick injury or other potential exposure. It is taken by mouth once a day.
Common side effects include headache, nausea, yellowish skin, abdominal pain, trouble sleeping, and fever. Severe side effects include rashes such as erythema multiforme and high blood sugar. Atazanavir appears to be safe to use during pregnancy. It is of the protease inhibitor (PI) class and works by blocking HIV protease.
Atazanavir was approved for medical use in the United States in 2003. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. In the United States it is not available as a generic medication. The wholesale cost in the developing world is about US$15.72 per month. As of 2015, the cost for a typical month of medication in the United States was more than $200.
Histamine
Histamine is derived from the decarboxylation of the amino acid histidine, a reaction catalyzed by the enzyme L-histidine decarboxylase. It is a hydrophilic vasoactive amine.
Anti-histone antibodies
Anti-histone antibodies are autoantibodies that are a subset of the anti-nuclear antibody family, which specifically target histone protein subunits or histone complexes. They were first reported by Henry Kunkel, H.R. Holman, and H.R.G. Dreicher in their studies of cellular causes of Lupus erythematosus in 1959-60. Today, anti-histone antibodies are still used as a marker for Systemic Lupus Erythematosus, but are also implicated in other autoimmune diseases like Sjogren's Syndrome, dermatomyositis, or rheumatoid arthritis.
Allergic rhinitis
Antihistamine drugs can have undesirable side-effects, the most notable one being drowsiness in the case of oral antihistamine tablets. First-generation antihistamine drugs such as diphenhydramine cause drowsiness, while second- and third-generation antihistamines such as cetirizine and loratadine are less likely to.
Allergic rhinitis
It is best to take oral antihistamine medication before exposure, especially for seasonal allergic rhinitis. In the case of nasal antihistamines like azelastine antihistamine nasal spray, relief from symptoms is experienced within 15 minutes allowing for a more immediate 'as-needed' approach to dosage. There is not enough evidence of antihistamine efficacy as an add-on therapy with nasal steroids in the management of intermittent or persistent allergic rhinitis in children, so its adverse effects and additional costs must be considered.
Levocetirizine
Levocetirizine is an antihistamine. It acts as an inverse agonist that decreases activity at histamine H1 receptors. This in turn prevents the release of other allergy chemicals and increase the blood supply to the area, and provides relief from the typical symptoms of hay fever.
Pheniramine
Pheniramine (INN, trade name Avil, among others) is an antihistamine with anticholinergic properties used to treat allergic conditions such as hay fever or urticaria. It has relatively strong sedative effects, and may sometimes be used off-label as an over-the-counter sleeping pill in a similar manner to other sedating antihistamines such as diphenhydramine. Pheniramine is also commonly found in eyedrops used for the treatment of allergic conjunctivitis.
Sleep disorder
Histamine plays a role in wakefulness in the brain. An allergic reaction over produces histamine causing wakefulness and inhibiting sleep Sleep problems are common in people with allergic rhinitis. A study from the N.I.H. found that sleep is dramatically impaired by allergic symptoms and that the degree of impairment is related to the severity of those symptoms s Treatment of allergies has also been shown to help sleep apnea.
Hives
The mainstay of therapy for both acute and chronic hives is patient education, avoiding triggers and using antihistamines.
Histamine
Libido loss and erectile failure can occur during treatment with histamine H receptor antagonists such as cimetidine, ranitidine, and risperidone. The injection of histamine into the corpus cavernosum in men with psychogenic impotence produces full or partial erections in 74% of them. It has been suggested that H antagonists may cause sexual difficulties by reducing the uptake of testosterone.
Antihistamine
H-antihistamines refer to compounds that inhibit the activity of the H receptor. Since the H receptor exhibits constitutive activity, H-antihistamines can be either neutral receptor antagonists or inverse agonists. Normally, histamine binds to the H receptor and heightens the receptor's activity; the receptor antagonists work by binding to the receptor and blocking the activation of the receptor by histamine; by comparison, the inverse agonists bind to the receptor and reduce its activity, an effect which is opposite to histamine's.
Nasal spray
Antihistamines work by competing for receptor sites to block the function of histamine, thereby reducing the inflammatory effect. Antihistamine nasal sprays include:Corticosteroid nasal sprays can be used to relieve the symptoms of sinusitis, hay fever, allergic rhinitis and non-allergic (perennial) rhinitis. They can reduce inflammation and histamine production in the nasal passages, and have been shown to relieve nasal congestion, runny nose, itchy nose and sneezing. Side effects may include headaches, nausea and nose bleeds. Corticosteroid nasal sprays include:Influenza vaccine is available in the form of a nasal spray like Live attenuated influenza vaccine (LAIV).
Hives
Severe reactions can be seen with exposure to cold water; swimming in cold water is the most common cause of a severe reaction. This can cause a massive discharge of histamine, resulting in low blood pressure, fainting, shock and even loss of life. Cold urticaria is diagnosed by dabbing an ice cube against the skin of the forearm for 1 to 5 minutes. A distinct hive should develop if a patient suffers cold urticaria. This is different from the normal redness that can be seen in people without cold urticaria. Patients with cold urticaria need to learn to protect themselves from a hasty drop in body temperature. Regular antihistamines are not generally efficacious. One particular antihistamine, cyproheptadine (Periactin), has been found to be useful. The tricyclic antidepressant doxepin has also been found to be an effective blocking agent of histamine discharge. Finally, a medication named ketotifen, which keeps mast cells from discharging histamine, has also been employed with widespread success.
Recreational drug use
Antihistamines (or "histamine antagonists") inhibit the release or action of histamine. "Antihistamine" can be used to describe any histamine antagonist, but the term is usually reserved for the classical antihistamines that act upon the H histamine receptor. Antihistamines are used as treatment for allergies. Allergies are caused by an excessive response of the body to allergens, such as the pollen released by grasses and trees. An allergic reaction causes release of histamine by the body. Other uses of antihistamines are to help with normal symptoms of insect stings even if there is no allergic reaction. Their recreational appeal exists mainly due to their anticholinergic properties, that induce anxiolysis and, in some cases such as diphenhydramine, chlorpheniramine, and orphenadrine, a characteristic euphoria at moderate doses. High dosages taken to induce recreational drug effects may lead to overdoses. Antihistamines are also consumed in combination with alcohol, particularly by youth who find it hard to obtain alcohol. The combination of the two drugs can cause intoxication with lower alcohol doses.
Cloperastine
Cloperastine (INN) or cloperastin, also known as cloperastine hydrochloride (JAN) (brand names Hustazol, Nitossil, Seki) and cloperastine fendizoate (or hybenzoate), is an antitussive and antihistamine that is marketed as a cough suppressant in Japan, Hong Kong, and in some European countries. It was first introduced in 1972 in Japan, and then in Italy in 1981. The precise mechanism of action of cloperastine is not fully clear, but several different biological activities have been identified for the drug, of which include: ligand of the σ receptor (K = 20 nM) (likely an agonist), GIRK channel blocker (described as "potent"), antihistamine (K = 3.8 nM for the H receptor), and anticholinergic. It is thought that the latter two properties contribute to side effects, such as sedation and somnolence, while the former two may be involved in or responsible for the antitussive efficacy of cloperastine.
Histamine H3 receptor
This receptor has been proposed as a target for treating sleep disorders. The receptor has also been proposed as a target for treating neuropathic pain.
Immunoglobulin E
Currently, allergic diseases and asthma are usually treated with one or more of the following drugs: (1) antihistamines and antileukotrienes, which antagonize the inflammatory mediators histamine and leukotrienes, (2) local or systemic (oral or injectable) corticosteroids, which suppress a broad spectrum of inflammatory mechanisms, (3) short or long-acting bronchodilators, which relax smooth muscle of constricted airway in asthma, or (4) mast cell stabilizers, which inhibit the degranulation of mast cells that is normally triggered by IgE-binding at FcεRI. Long-term uses of systemic corticosteroids are known to cause many serious side effects and are advisable to avoid, if alternative therapies are available.
Physical urticaria
Antihistamine agents are the typically prescribed drug for the treatment of physical urticaria. They block the effect of histamine, a compound produced by the body which forms a part of the local immune response consequently causing inflammation. Some research has suggested that the use antihistamines and antagonist in synergy are better for the treatment of physical urticarias.
Histamine
While histamine has stimulatory effects upon neurons, it also has suppressive ones that protect against the susceptibility to convulsion, drug sensitization, denervation supersensitivity, ischemic lesions and stress. It has also been suggested that histamine controls the mechanisms by which memories and learning are forgotten.
Recall (memory)
State-dependent retrieval is demonstrated when material learned under one State is best recalled in that same state. A study by Carter and Cassady (1998) showed this effect with antihistamine. In other words, if you study while on hay fever tablets, then you will recall more of what you studied if you test yourself while on antihistamines in comparison to testing yourself while not on antihistamines after having studied on antihistamines.
Doxepin
Antidepressant doses of doxepin are defined as 25 to 300 mg/day, although are typically above 75 mg/day. Antihistamine doses, including for dermatological uses and as a sedative/hypnotic for insomnia, are considered to be 3 to 25 mg, although higher doses between 25 and 50 mg and in some cases even up to 150 mg have been used to treat insomnia. At low doses, below 25 mg, doxepin is a pure antihistamine. At antidepressant doses of above 25 mg, doxepin has significant antiadrenergic, antiserotonergic, and anticholinergic effects, and these activities contribute to its side effects.
H2 antagonist
In 1964, it was known that histamine stimulated the secretion of stomach acid, and also that traditional antihistamines had no effect on acid production. From these facts the SK&F scientists postulated the existence of two different types of histamine receptors. They designated the one acted upon by the traditional antihistamines as H, and the one acted upon by histamine to stimulate the secretion of stomach acid as H.
Trimipramine
Trimipramine is a very potent antihistamine; it has the third highest affinity for the H receptor (K = 0.27 nM) after mirtazapine (K = 0.14 nM) and doxepin (K = 0.24 nM) among the TCAs and tetracyclic antidepressants (TeCAs). The TeCA mianserin (K = 0.40) and the TCA amitriptyline (K = 1.0) are also very potent H receptor antagonists, whereas other TCAs and TeCAs are less potent. These TCAs and TeCAs, including trimipramine, are far more potent than the standard antihistamine diphenhydramine (approximately 800 times for doxepin and 250 times for trimipramine), and are among the most potent antihistamines available.
Allergic transfusion reaction
There is no evidence that antihistamine premedication prevents allergic transfusion reactions, although these drugs can mitigate symptoms once they occur.
Cetirizine
Cetirizine crosses the blood–brain barrier only slightly, and for this reason, it produces minimal sedation compared to many other antihistamines. A positron emission tomography (PET) study found that brain occupancy of the H receptor was 12.6% for 10 mg cetirizine, 25.2% for 20 mg cetirizine, and 67.6% for 30 mg hydroxyzine. (A 10 mg dose of cetirizine equals about a 30 mg dose of hydroxyzine in terms of peripheral antihistamine effect.) PET studies with antihistamines have found that brain H receptor occupancy of more than 50% is associated with a high prevalence of somnolence and cognitive decline, whereas brain H receptor occupancy of less than 20% is considered to be non-sedative. In accordance, H receptor occupancy correlated well with subjective sleepiness for 30 mg hydroxyzine but there was no correlation for 10 or 20 mg cetirizine. As such, brain penetration and brain H receptor occupancy by cetirizine are dose-dependent, and in accordance, while cetirizine at doses of 5 to 10 mg have been reported to be non-sedating or mildly sedating, a higher dose of 20 mg has been found to induce significant drowsiness in other studies.
Epigenetics of schizophrenia
HMT (histone demethylase) inhibitors also act on histones. They prevent the demethylation of the H3K4 histone protein and open up that part of the chromatin. Tranylcypromine, an antidepressant, has been shown to have HMT inhibitory properties, and in a study, treatment of patients with schizophrenia with tranylcypromine showed improvements regarding negative symptoms.
Antiviral drug
An improved knowledge of the action of reverse transcriptase has led to better nucleoside analogues to treat HIV infections. One of these drugs, lamivudine, has been approved to treat hepatitis B, which uses reverse transcriptase as part of its replication process. Researchers have gone further and developed inhibitors that do not look like nucleosides, but can still block reverse transcriptase.
Allergic conjunctivitis
Treatment of allergic conjunctivitis is by avoiding the allergen ("e.g.", avoiding grass in bloom during "hay fever season") and treatment with antihistamines, either topical (in the form of eye drops), or systemic (in the form of tablets). Antihistamines, medications that stabilize mast cells, and nonsteroidal anti-inflammatory drugs (NSAIDs) are generally safe and usually effective.
Allergic conjunctivitis
Antihistamines such as diphenhydramine and chlorpheniramine are commonly used as treatment. People treated with H1 antihistamines exhibit reduced production of histamine and leukotrienes as well as downregulation of adhesion molecule expression on the vasculature which in turn attenuates allergic symptoms by 40–50%.
H1 antagonist
Histamine, acting on H-receptors, produces pruritus, vasodilation, hypotension, flushing, headache, bradycardia, bronchoconstriction, increase in vascular permeability and potentiation of pain.
Thiazinamium metilsulfate
Since many of the uses of antihistamines involve conditions such as rashes, which should be treatable by local application, there is some rationale for developing drugs for topical use. The known side effects of antihistamines could in principle be avoided if the drug were functionalized to avoid systemic absorption. The known poor absorption of quat salts make such derivatives attractive for nonabsorbable antihistamines for topical use.
Histamine
The most important pathophysiologic mechanism of mast cell and basophil histamine release is immunologic. These cells, if sensitized by IgE antibodies attached to their membranes, degranulate when exposed to the appropriate antigen. Certain amines and alkaloids, including such drugs as morphine, and curare alkaloids, can displace histamine in granules and cause its release. Antibiotics like polymyxin are also found to stimulate histamine release.
Antihistamine
These are experimental agents and do not yet have a defined clinical use, although a number of drugs are currently in human trials. H-antihistamines have a stimulant and nootropic effect, whereas H-antihistamines appear to have an immunomodulatory role.
Oral allergy syndrome
Antihistamines may also relieve the symptoms of the allergy by blocking the immune pathway. Persons with a history of severe anaphylactic reaction may carry an injectable emergency dose of epinephrine (such as an EpiPen). Oral steroids may also be helpful. Allergy immunotherapy has been reported to improve or cure OAS in some patients. Immunotherapy with extracts containing birch pollen may benefit OAS sufferers of apple or hazelnut related to birch pollen-allergens. Even so, the increase in the amount of apple/hazelnut tolerated was small (from 12.6 to 32.6 g apple), and as a result, a patient's management of OAS would be limited.
Ciproxifan
The histamine H receptor is an inhibitory autoreceptor located on histaminergic nerve terminals, and is believed to be involved in modulating the release of histamine in the brain. Histamine has an excitatory effect in the brain via H receptors in the cerebral cortex, and so drugs such as ciproxifan which block the H receptor and consequently allow more histamine to be released have an alertness-promoting effect.
Antiandrogen
Antiandrogens are used in the treatment of androgen-dependent skin and hair conditions including acne, seborrhea, hidradenitis suppurativa, hirsutism, and pattern hair loss in women. All of these conditions are dependent on androgens, and for this reason, antiandrogens are effective in treating them. The most commonly used antiandrogens for these indications are cyproterone acetate and spironolactone. Flutamide has also been studied extensively for such uses, but has fallen out of favor due to its association with hepatotoxicity. Bicalutamide, which has a relatively minimal risk of hepatotoxicity, has been evaluated for the treatment of hirsutism and found effective similarly to flutamide and may be used instead of it. In addition to AR antagonists, oral contraceptives containing ethinylestradiol are effective in treating these conditions, and may be combined with AR antagonists.
Diphenhydramine
Diphenhydramine, while traditionally known as an antagonist, acts primarily as an inverse agonist of the histamine H receptor. It is a member of the ethanolamine class of antihistaminergic agents. By reversing the effects of histamine on the capillaries, it can reduce the intensity of allergic symptoms. It also crosses the blood–brain barrier and inversely agonizes the H receptors centrally. Its effects on central H receptors cause drowsiness.
Antihistamine
Inhibit the action of histidine decarboxylase:
Setastine
Setastine (Loderix) is an antihistamine used to treat allergies and rhinitis.
Histamine
When injected intravenously, histamine causes most blood vessels to dilate, and hence causes a fall in the blood pressure. This is a key mechanism in anaphylaxis, and is thought to be caused when histamine releases nitric oxide, endothelium-derived hyperpolarizing factors and other compounds from the endothelial cells.
Fexofenadine
Fexofenadine is a selectively peripheral H1-blocker. Blockage prevents the activation of the H1 receptors by histamine, preventing the symptoms associated with allergies from occurring. Fexofenadine does not readily cross the blood–brain barrier and is therefore less likely to cause drowsiness in comparison to other antihistamines that readily cross the blood-brain barrier (i.e. first-generation antihistamines like diphenhydramine). In general, fexofenadine takes about one hour to take effect, though this may be affected by the choice of dosage form and the presence/absence of certain foods.
Pollen
Antihistamines are effective at treating mild cases of pollinosis, this type of non-prescribed drugs includes loratadine, cetirizine and chlorpheniramine. They do not prevent the discharge of histamine, but it has been proven that they do prevent a part of the chain reaction activated by this biogenic amine, which considerably lowers hay fever symptoms.
Histamine agonist
A histamine agonist is a drug which causes increased activity at one or more of the four histamine receptor subtypes.
Clemastine
Clemastine, also known as meclastin, is an antihistamine and anticholinergic. Unlike loratadine or fexofenadine, clemastine is a sedating antihistamine; however, it exhibits fewer other side effects than most of the widely used antihistamines. Clemastine is also classified as an antipruritic (i.e., it stops itching).
Histapyrrodine
Histapyrrodine is an antihistamine with anticholinergic properties.
Histidine decarboxylase
Antihistamines are a class of medications designed to reduce unwanted effects of histamine in the body. Typical antihistamines block specific histamine receptors, depending on what physiological purpose they serve. For example, diphenhydramine (Benadryl™), targets and inhibits the H1 histamine receptor to relieve symptoms of allergic reactions. Inhibitors of histidine decarboxylase can conceivably be used as atypical antihistamines. Tritoqualine, as well as various catechins, such as epigallocatechin-3-gallate, a major component of green tea, have been shown to target HDC and histamine-producing cells, reducing histamine levels and providing anti-inflammatory, anti-tumoral, and anti-angiogenic effects.
Doxepin
Doxepin is a highly potent antihistamine, with this being its strongest activity. In fact, doxepin has been said to be the most or one of the most potent H receptor antagonists available, with one study finding an "in vitro" K of 0.17 nM. It is the most potent and selective H receptor antagonist of the TCAs (although the "tetracyclic" antidepressant (TeCA) mirtazapine is slightly more potent), and other sedating antihistamines, for instance the over-the-counter diphenhydramine (K = 16 nM) and doxylamine (K = 42 nM), show far lower affinities for this receptor in comparison. The affinity of doxepin for the H receptor is far greater than its affinity for other sites, and 10- to 100-fold higher doses are needed for antidepressant effects. In accordance, although it is often described as a "dirty drug" due to its highly promiscuous binding profile, doxepin acts as a highly selective antagonist of the H receptor at very low doses (less than 10 mg; typically 3 to 6 mg). At these doses, it notably has no clinically relevant anticholinergic effects such as dry mouth or cognitive/memory impairment, unlike most other sedating antihistamines, and similarly has no effect on other receptors such as adrenergic and serotonin receptors.
Clemastine
Clemastine is an antihistamine with anticholinergic and sedative effects. Antihistamines competitively bind to histamine receptor sites, thus reducing the neurotransmitter's effects. Effects of histamine (which are countered by antihistamines) include:
Antihistamine
Antihistamines suppress the histamine-induced wheal response (swelling) and flare response (vasodilation) by blocking the binding of histamine to its receptors or reducing histamine receptor activity on nerves, vascular smooth muscle, glandular cells, endothelium, and mast cells.
Mepyramine
Mepyramine, also known as pyrilamine, is a first generation antihistamine, targeting the H receptor. It rapidly permeates the brain often causing drowsiness. It also has anticholinergic properties. However, its anticholinergic potency is negligible compared to its antihistaminergic activity; it has an H to muscarinic K ratio of 130,000 to 1, compared to a ratio of 20 to 1 for diphenhydramine. It is used in over-the-counter combination products to treat the common cold and menstrual symptoms. It is also the active ingredient of the topical antihistamine creams "Anthisan" and "Neoantergan", sold for the treatment of insect bites, stings, and nettle rash.
Zidovudine
Zidovudine (ZDV), also known as azidothymidine (AZT), is an antiretroviral medication used to prevent and treat HIV/AIDS. It is generally recommended for use with other antiretrovirals. It may be used to prevent mother-to-child spread during birth or after a needlestick injury or other potential exposure. It is sold both by itself and together as lamivudine/zidovudine and abacavir/lamivudine/zidovudine. It can be used by mouth or by slow injection into a vein.
Common side effects include headaches, fever, and nausea. Serious side effects include liver problems, muscle damage, and high blood lactate levels. It is commonly used in pregnancy and appears to be safe for the baby. ZDV is of the nucleoside analog reverse-transcriptase inhibitor (NRTI) class. It works by inhibiting the enzyme reverse transcriptase that HIV uses to make DNA and therefore decreases replication of the virus.
Zidovudine was first described in 1964. It was approved in the United States in 1986 and was the first treatment for HIV. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. It is available as a generic medication. The wholesale cost in the developing world is US$5.10 to $25.60 per month. As of 2015, the cost for a typical month of medication in the United States was more than $200.
Mast cell
Histamine is a vasodilatory substance released during anaphylaxis.
Antihistamine
Itching, sneezing, and inflammatory responses are suppressed by antihistamines that act on H1-receptors. In 2014 antihistamines such as desloratadine were found to be effective as adjuvants to standardized treatment of acne due to their anti-inflammatory properties and their ability to suppress sebum production.
Talastine
Talastine (trade name Ahanon) is an antihistamine.
Antihistamine
Antihistamines can vary greatly in cost. Some patients consult with their doctor about drug prices to make a decision about which antihistamine to choose. Many antihistamines are older and available in generic form. Others are newer, still under patent, and generally expensive. The newer drugs are not necessarily safer or more effective. Because so many antihistamines are available, patients can have conversations with their health care provider to choose the right drug for them.
JNJ-7777120
JNJ-7777120 is a drug being developed by Johnson & Johnson Pharmaceutical Research & Development which acts as a potent and selective antagonist at the histamine H receptor. It has anti-inflammatory effects, and has been demonstrated to be superior to traditional antihistamines in the treatment of pruritus (itching).
Hives
Oral glucocorticoids are effective in controlling symptoms of chronic hives however they have an extensive list of adverse effects such as adrenal suppression, weight gain, osteoporosis, hyperglycemia, etc. Therefore, their use should be limited to a couple of weeks. In addition, one study found that systemic glucocorticoids combined with antihistamines did not hasten the time to symptom control compared with antihistamines alone.
Histoplasmosis
In the majority of immunocompetent individuals, histoplasmosis resolves without any treatment. Antifungal medications are used to treat severe cases of acute histoplasmosis and all cases of chronic and disseminated disease. Typical treatment of severe disease first involves treatment with amphotericin B, followed by oral itraconazole.
Anti-Hu associated encephalitis
Some treatments may directly combat the mechanisms by which the disease may be caused. To suppress the immune system, steroids, antibodies, or even human cells may be injected into a patient. Certain types of antibodies called intravenous immunoglobulins (IVIG) also have shown to lead to reduced symptoms due to their ability to reduce and eliminate anti-Hu antibodies. A drug called rituximab, a molecule that targets T cells, helps reduce the symptoms of anti-Hu encephalitis and decreases the number of anti-Hu antibodies. Cancer treatment may involve surgical removal of the tumor, or medications that may shrink or eliminate the tumor. Treatment with cyclophosphamide, a chemotherapy drug, has shown promise, in addition to adrenocorticotropic hormone (ACTH). This hormone is involved in regulating many body functions including stress level and blood pressure. Steroids such as dexamethasone may help reduce disease burden by reducing the antibody-building activity of the disease. Despite the fact that steroids can be used to reduce the immunological antibody-building activity of the disease in all people, many other anti-Hu encephalitis treatments are most effective in children.
Antihistamine
Examples include:
Epinastine
Epinastine (brand names Alesion, Elestat, Purivist, Relestat) is a second-generation antihistamine and mast cell stabilizer that is used in eye drops to treat allergic conjunctivitis. It is produced by Allergan and marketed by Inspire in the United States. It is highly selective for the H receptor and does not cross the blood-brain-barrier.
Histamine H1 receptor
The tuberomammillary nucleus is a histaminergic nucleus that strongly regulates the sleep-wake cycle. H-antihistamines that cross the blood-brain barrier inhibit H receptor activity on neurons that project from the tuberomammillary nucleus. This action is responsible for the drowsiness effect associated with these drugs.
Laryngitis
When treating allergic laryngitis, topical nasal steroids and immunotherapy have been found to be effective for allergic rhinitis. Antihistamines may also be helpful, but can create a dryness in the larynx. Inhaled steroids that are used for a long period can lead to problems with the larynx and voice.
Post-nasal drip
Treatment options depend on the nature of an individual’s post-nasal drip and its cause. Antibiotics may be prescribed if the PND is the result of a bacterial infection. Antihistamines are recommended if the PND is caused by allergies. First-generation antihistamines can have side effects including drowsiness however. Nasal steroid treatments, such as fluticasone propionate, may also provide relief. Decongestants such as Sudafed cause a reduction in membranes through the tightening of blood vessels which resultantly limit PND.
Clemastine
Clemastine is a selective histamine H antagonist. It binds to the histamine H receptor, thus blocking the action of endogenous histamine, which leads to temporary relief of the negative symptoms caused by histamine.
Histamine
Enterochromaffin-like cells, located within the gastric glands of the stomach, release histamine that stimulates nearby parietal cells by binding to the apical H receptor. Stimulation of the parietal cell induces the uptake of carbon dioxide and water from the blood, which is then converted to carbonic acid by the enzyme carbonic anhydrase. Inside the cytoplasm of the parietal cell, the carbonic acid readily dissociates into hydrogen and bicarbonate ions. The bicarbonate ions diffuse back through the basilar membrane and into the bloodstream, while the hydrogen ions are pumped into the lumen of the stomach via a K/H ATPase pump. Histamine release is halted when the pH of the stomach starts to decrease. Antagonist molecules, like ranitidine, block the H receptor and prevent histamine from binding, causing decreased hydrogen ion secretion.