It was first made by Union Chimique Belge in 1956 and was approved for sale by Pfizer in the United States later that year.[8][10] In 2022, it was the 46th most commonly prescribed medication in the United States, with more than 13million prescriptions.[11][12]
Doses of hydroxyzine hydrochloride used for sleep range from 25 to 100 mg.[15][16][17] As with other antihistamine sleep aids, hydroxyzine is usually only prescribed for short term or "as-needed" use since tolerance to the CNS (central nervous system) effects of hydroxyzine can develop in as little as a few days.[18][non-primary source needed] A major systematic review and network meta-analysis of medications for the treatment of insomnia published in 2022 found little evidence to inform the use of hydroxyzine for insomnia.[19] A 2023 meta-review concludes that hydroxyzine is effective for inducing sleep onset but less effective for maintaining sleep for eight hours.[20]
Gabasync
Gabasync, a treatment consisting of a combination of hydroxyzine and two other medications (gabapentin and flumazenil) as well as therapy, is an ineffective treatment promoted for methamphetamine addiction, though it had also been claimed to be effective for dependence on alcohol or cocaine.[21] It was marketed as PROMETA. While the individual drugs had been approved by the FDA, their off-label use for addiction treatment has not.[22] Gabasync was marketed by Hythiam, Inc. which is owned by Terren Peizer, a former bond salesman who has since been indicted for securities fraud relative to another company.[23][24] Hythiam charges up to $15,000 per patient to license its use (of which half goes to the prescribing physician, and half to Hythiam).[25]
In November 2011, the results of a double-blind, placebo-controlled study (financed by Hythiam and carried out at UCLA) were published in the peer-reviewed journal Addiction. It concluded that Gabasync is ineffective: "The PROMETA protocol, consisting of flumazenil, gabapentin and hydroxyzine, appears to be no more effective than placebo in reducing methamphetamine use, retaining patients in treatment or reducing methamphetamine craving."[26]
The administration of hydroxyzine in large amounts by ingestion or intramuscular administration during the onset of pregnancy can cause fetal abnormalities. When administered to pregnant rats, mice and rabbits, hydroxyzine caused abnormalities such as hypogonadism with doses significantly above that of the human therapeutic range.[29][better source needed]
In humans, a significant dose has not yet been established in studies and, by default, the Food and Drug Administration (FDA) has introduced contraindication guidelines in regard to hydroxyzine.[29] Use by those at risk for or showing previous signs of hypersensitivity is also contraindicated.[29]
Other contraindications include the administration of hydroxyzine alongside depressants and other compounds which affect the central nervous system;[29] if absolutely necessary, it should only be administered concomitantly in small doses.[29] If administered in small doses with other substances, as mentioned, then patients should refrain from using dangerous machinery, motor vehicles or any other practice requiring absolute concentration, in accordance with safety laws.[29]
Studies have also been conducted which show that long-term prescription of hydroxyzine can lead to tardive dyskinesia after years of use, but effects related to dyskinesia have also anecdotally been reported after periods of 7.5 months,[30] such as continual head rolling, lip licking and other forms of athetoid movement. In certain cases, elderly patients' previous interactions with phenothiazine derivatives or pre-existing neuroleptic treatment may have contributed to dyskinesia at the administration of hydroxyzine due to hypersensitivity caused by prolonged treatment,[30] and therefore some contraindication is given for short-term administration of hydroxyzine to those with previous phenothiazine use.[30]
Side effects
Several reactions have been noted in manufacturer guidelines—deep sleep, incoordination, sedation, calmness, and dizziness have been reported in children and adults, as well as others such as hypotension, tinnitus, and headaches.[31]Gastrointestinal effects have also been observed, as well as less serious effects such as dryness of the mouth and constipation caused by the mild antimuscarinic properties of hydroxyzine.[31]
Atarax
Central nervous system effects such as hallucinations or confusion have been observed in rare cases, attributed mostly to overdosage.[32][31] Such properties have been attributed to hydroxyzine in several cases, particularly in patients treated for neuropsychological disorders, as well as in cases where overdoses have been observed. While there are reports of the "hallucinogenic" or "hypnotic" properties of hydroxyzine, several clinical data trials have not reported such side effects from the sole consumption of hydroxyzine, but rather, have described its overall calming effect described through the stimulation of areas within the reticular formation. The hallucinogenic or hypnotic properties have been described as being an additional effect from overall central nervous system suppression by other CNS agents, such as lithium or ethanol.[33]
Hydroxyzine exhibits anxiolytic and sedative properties in many psychiatric patients. One study showed that patients reported very high levels of subjective sedation when first taking the drug, but that levels of reported sedation decreased markedly over 5–7 days, likely due to CNS receptor desensitization. Other studies have suggested that hydroxyzine acts as an acute hypnotic, reducing sleep onset latency and increasing sleep duration — also showing that some drowsiness did occur. This was observed more in female patients, who also had greater hypnotic response.[34] The use of sedating drugs alongside hydroxyzine can cause oversedation and confusion if administered at high doses—any form of hydroxyzine treatment alongside sedatives should be done under supervision of a doctor.[35][32]
Because of the potential for more severe side effects, this drug is on the list to avoid in the elderly.[36]
Hydroxyzine crosses the blood–brain barrier easily and exerts effects in the central nervous system.[46] A positron emission tomography (PET) study found that brain occupancy of the H1 receptor was 67.6% for a single 30 mg dose of hydroxyzine.[52] In addition, subjective sleepiness correlated well with the brain H1 receptor occupancy.[52] PET studies with antihistamines have found that brain H1 receptor occupancy of more than 50% is associated with a high prevalence of somnolence and cognitive decline, whereas brain H1 receptor occupancy of less than 20% is considered to be non-sedative.[53]
Hydroxyzine can be administered orally or via intramuscular injection. When given orally, hydroxyzine is rapidly absorbed from the gastrointestinal tract. Hydroxyzine is rapidly absorbed and distributed with oral and intramuscular administration, and is metabolized in the liver; the main metabolite (45%), cetirizine, is formed through oxidation of the alcohol moiety to a carboxylic acid by alcohol dehydrogenase, and overall effects are observed within one hour of administration. Higher concentrations are found in the skin than in the plasma. Cetirizine, although less sedating, is non-dialyzable and possesses similar antihistamine properties. The other metabolites identified include a N-dealkylated metabolite, and an O-dealkylated 1/16 metabolite with a plasma half-life of 59 hours. These pathways are mediated principally by CYP3A4 and CYP3A5.[55][56] The N-dealykylated metabolite, norchlorcyclizine, bears some structural similarities to trazodone, but it has not been established whether it is pharmacologically active.[57][58] In animals, hydroxyzine and its metabolites are excreted in feces primarily through biliary elimination.[59][60] In rats, less than 2% of the drug is excreted unchanged.[60]
The time to reach maximum concentration (Tmax) of hydroxyzine is about 2.0 hours in both adults and children and its elimination half-life is around 20.0 hours in adults (mean age 29.3 years) and 7.1 hours in children.[5][6] Its elimination half-life is shorter in children compared to adults.[5] In another study, the elimination half-life of hydroxyzine in elderly adults was 29.3 hours.[7] One study found that the elimination half-life of hydroxyzine in adults was as short as 3 hours, but this may have just been due to methodological limitations.[61] Although hydroxyzine has a long elimination half-life and acts, in-vivo, as an antihistamine for as long as 24 hours, the predominant CNS effects of hydroxyzine and other antihistamines with long half-lives seem to diminish after 8 hours.[62]
Administration in geriatrics differs from the administration of hydroxyzine in younger patients; according to the FDA, there have not been significant studies made (2004), which include population groups over 65, which provide a distinction between elderly aged patients and other younger groups. Hydroxyzine should be administered carefully in the elderly with consideration given to possible reduced elimination.[32][better source needed]
Hydroxyzine is supplied mainly as a dihydrochloridesalt (hydroxyzine hydrochloride) but also to a lesser extent as an embonate salt (hydroxyzine pamoate).[63][64][65] The molecular weights of hydroxyzine, hydroxyzine dihydrochloride, and hydroxyzine pamoate are 374.9 g/mol, 447.8 g/mol, and 763.3 g/mol, respectively.[4] Due to their differences in molecular weight, 1 mg hydroxyzine dihydrochloride is equivalent to about 1.7 mg hydroxyzine pamoate.[66]
Hydroxyzine preparations require a doctor's prescription. The drug is available in two formulations, the pamoate and the dihydrochloride or hydrochloridesalts. Vistaril, Equipose, Masmoran, and Paxistil are preparations of the pamoate salt, while Atarax, Alamon, Aterax, Durrax, Tran-Q, Orgatrax, Quiess, and Tranquizine are of the hydrochloride salt.
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^ abcdefgSnowman AM, Snyder SH (December 1990). "Cetirizine: actions on neurotransmitter receptors". The Journal of Allergy and Clinical Immunology. 86 (6 Pt 2): 1025–1028. doi:10.1016/S0091-6749(05)80248-9. PMID1979798.
^ abLim HD, van Rijn RM, Ling P, Bakker RA, Thurmond RL, Leurs R (September 2005). "Evaluation of histamine H1-, H2-, and H3-receptor ligands at the human histamine H4 receptor: identification of 4-methylhistamine as the first potent and selective H4 receptor agonist". The Journal of Pharmacology and Experimental Therapeutics. 314 (3): 1310–1321. doi:10.1124/jpet.105.087965. PMID15947036. S2CID24248896.
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^Orzechowski RF, Currie DS, Valancius CA (January 2005). "Comparative anticholinergic activities of 10 histamine H1 receptor antagonists in two functional models". European Journal of Pharmacology. 506 (3): 257–264. doi:10.1016/j.ejphar.2004.11.006. PMID15627436.
^Lamberty Y, Gower AJ (September 2004). "Hydroxyzine prevents isolation-induced vocalization in guinea pig pups: comparison with chlorpheniramine and immepip". Pharmacology, Biochemistry, and Behavior. 79 (1): 119–124. doi:10.1016/j.pbb.2004.06.015. PMID15388291. S2CID23593514.
^ abTashiro M, Kato M, Miyake M, Watanuki S, Funaki Y, Ishikawa Y, et al. (October 2009). "Dose dependency of brain histamine H(1) receptor occupancy following oral administration of cetirizine hydrochloride measured using PET with [11C]doxepin". Human Psychopharmacology. 24 (7): 540–548. doi:10.1002/hup.1051. PMID19697300. S2CID5596000.
^Yanai K, Tashiro M (January 2007). "The physiological and pathophysiological roles of neuronal histamine: an insight from human positron emission tomography studies". Pharmacology & Therapeutics. 113 (1): 1–15. doi:10.1016/j.pharmthera.2006.06.008. PMID16890992.
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