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| Pronunciation | /sɛˈtɪrɪziːn/ ⓘ |
| Trade names | Zyrtec, others |
| AHFS/Drugs.com | Monograph |
| MedlinePlus | a698026 |
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| Routes of administration | By mouth |
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| Bioavailability | Well-absorbed (>70%)[7] |
| Protein binding | 88–96%[7] |
| Metabolism | Minimal (non-cytochrome P450-mediated)[9][8] |
| Onset of action | 20–42 minutes[8] |
| Eliminationhalf-life | Mean: 8.3 hours[9][8] Range: 6.5–10 hours[10] |
| Duration of action | ≥24 hours[10] |
| Excretion | Urine: 70–85%[9] Feces: 10–13%[9] |
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| ECHA InfoCard | 100.223.545 |
| Chemical and physical data | |
| Formula | C21H25ClN2O3 |
| Molar mass | 388.89 g·mol−1 |
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Cetirizine is asecond-generation peripherally selective antihistamine used to treatallergic rhinitis (hay fever),dermatitis, andurticaria (hives).[11] It is takenby mouth.[12] Effects generally begin within thirty minutes and last for about a day.[12] The degree of benefit is similar to other antihistamines such asdiphenhydramine, which is afirst-generation antihistamine.[12]
Common side effects include sleepiness, dry mouth, headache, and abdominal pain.[12] The degree of sleepiness that occurs is generally less than withfirst-generation antihistamines because second-generation antihistamines are more selective for theH1 receptor.[13][11] Compared to other second-generation antihistamines, cetirizine can cause drowsiness.[13] Among second-generation antihistamines, cetirizine is more likely thanfexofenadine andloratadine to cause drowsiness.[13]
Use inpregnancy appears safe, but use duringbreastfeeding is not recommended.[14] The medication works by blockinghistamine H1 receptors, mostly outside thebrain.[12]
Cetirizine can be used for paediatric patients. The main side effect to be cautious about issomnolence.[15]
It was patented in 1983[16][17] and came into medical use in 1987.[18] Cetirizine is a therapeutic alternative on theWorld Health Organization's List of Essential Medicines.[19] It is available as ageneric medication.[11] In 2023, it was the 55th most commonly prescribed medication in the United States, with more than 11 million prescriptions.[20][21]
Cetirizine's primary indication is forhay fever and other allergies. Because the symptoms of itching and redness in these conditions are caused by histamine acting on the H1 receptor, blocking those receptors temporarily relieves those symptoms.[22]
Cetirizine is also commonly prescribed to treat acute and (in particular cases) chronicurticaria (hives), more efficiently than any other second-generation antihistamine.[22]
Cetirizine is available over-the-counter in the US in the form of 5 and 10 mgtablets. A 20 mg strength is available by prescription only.[9] It is also available as a 1 mg/mL syrup for oral administration by prescription. In the UK, up to 30 tablets of 10 mg are on the general sales list (of pharmaceuticals) and can be purchased without a prescription and pharmacist supervision.[23] The drug can be in the form of tablets, capsules or syrup.[23]
Commonly reported side effects of cetirizine includeheadache,dry mouth,drowsiness, andfatigue, while more serious, but rare, adverse effects reported includetachycardia andedema.[24]
Discontinuing cetirizine after prolonged use (typically, use beyond six months) may result in rare but severe generalizeditching, also called pruritus.[25] The itching generally occurs in patients who stop cetirizine after using the medication daily, and begins within a few days of stopping the medication. Although the mechanism by which cetirizine cessation causes itching is unknown, a case analysis by the FDA supports a causal relationship.[26]
The USFood and Drug Administration (FDA) analyzed cases of pruritus after stopping cetirizine in theFDA Adverse Event Reporting System (FAERS) database and medical literature through April 2017. Their report noted that some patients indicated the itchiness impacted their ability to work, sleep or perform normal daily activities.[25] On 16 May 2025, the FDA issued a Drug Safety Communication regarding the pruritus that can occur after discontinuing long-term use of cetirizine and levocetirizine.[26]
The FDA communication reports that symptoms would typically go away after restarting the medicine, and in some individuals were addressed by weaning off. No specific schedule for weaning is provided in the drug information for cetirizine.[26]
Cetirizine acts as a highlyselectiveantagonist of the histamine H1 receptor.[9] TheKi values for the H1 receptor are approximately 6 nM for cetirizine, 3 nM forlevocetirizine, and 100 nM fordextrocetirizine, indicating that thelevorotatoryenantiomer is the main active form.[9] Cetirizine has 600-fold or greaterselectivity for the H1 receptor over a wide variety of other sites, includingmuscarinic acetylcholine,serotonin,dopamine, andα-adrenergic receptors, among many others.[9] The drug shows 20,000-fold or greater selectivity for the H1 receptor over the five muscarinic acetylcholine receptors, and hence does not exhibitanticholinergic effects.[27][28] It shows negligible inhibition of thehERG channel (IC50Tooltip half-maximal inhibitory concentration > 30 μM)[29] and nocardiotoxicity has been observed with cetirizine at doses of up to 60 mg/day, six times the normal recommended dose[9] and the highest dose of cetirizine that has been studied in healthy subjects.[30]
Cetirizine crosses theblood–brain barrier only slightly, and for this reason, produces minimal sedation compared to many other antihistamines.[31] Apositron emission tomography (PET) study found that brain occupancy of the H1 receptor was 12.6% for 10 mg cetirizine, 25.2% for 20 mg cetirizine, and 67.6% for 30 mghydroxyzine.[32] (A 10 mg dose of cetirizine equals about a 30 mg dose of hydroxyzine in terms of peripheral antihistamine effect.)[33] 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.[34] In accordance, H1 receptor occupancy correlated well with subjective sleepiness for 30 mg hydroxyzine but there was no correlation for 10 or 20 mg cetirizine.[32] As such, brain penetration and brain H1 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.[32]
Cetirizine also shows anti-inflammatory properties independent of H1 receptors.[35] The effect is exhibited through suppression of theNF-κB pathway, and by regulating the release ofcytokines andchemokines, thereby regulating the recruitment of inflammatory cells.[36][37][38][39][40] It has been shown to inhibiteosinophilchemotaxis andLTB4 release.[41] At a dosage of 20 mg, Booneet al. found that it inhibited the expression ofVCAM-1 in patients withatopic dermatitis.[41]
Cetirizine is rapidly and extensivelyabsorbed uponoral administration in tablet or syrup form.[9] Theoralbioavailability of cetirizine is at least 70% and of levocetirizine is at least 85%.[7] TheTmax of cetirizine is approximately 1.0 hour regardless of formulation.[8] Thepharmacokinetics of cetirizine have been found to increase linearly with dose across a range of 5 to 60 mg.[9] ItsCmax following a single dose has been found to be 257 ng/mL for 10 mg and 580 ng/mL for 20 mg.[8] Food has no effect on the bioavailability of cetirizine but has been found to delay the Tmax by 1.7 hours (i.e., to approximately 2.7 hours) and to decrease the Cmax by 23%.[9][8][42] Similar findings were reported for levocetirizine, which had its Tmax delayed by 1.25 hours and its Cmax decreased by about 36% when administered with a high-fat meal.[42]Steady-state levels of cetirizine occur within 3 days and there is no accumulation of the drug with chronic administration.[8] Following once-daily administration of 10 mg cetirizine for ten days, the mean Cmax was 311 ng/mL.[43]
The meanplasma protein binding of cetirizine has been found to be 93 to 96% across a range of 25 to 1,000 ng/mL independent of concentration.[8] Plasma protein binding of 88 to 96% has also been reported across multiple studies.[7] The drug is bound toalbumin with highaffinity, whileα1-acid glycoprotein andlipoproteins contribute much less to total plasma protein binding.[7] The unbound or free fraction of levocetirizine has been reported to be 8%.[7] The truevolume of distribution of cetirizine is unknown but is estimated to be 0.3 to 0.45 L/kg.[9][7] Cetirizine poorly and slowly crosses theblood–brain barrier, which is thought to be due to its chemical properties and its activity as aP-glycoproteinsubstrate.[44][7][45]
Cetirizine is notably not metabolized by thecytochrome P450 system.[46] Because of this, it does not interact significantly with drugs thatinhibit orinduce cytochrome P450 enzymes such astheophylline,erythromycin,clarithromycin,cimetidine, oralcohol.[9] Studies with cetirizine synthesized with radioactive carbon-14 show that 90% of excreted cetirizine is unchanged at 2 hours, 80% at 10 hours, and 70% at 24 hours, indicating limited and slow metabolism.[8] While cetirizine does not undergo extensive metabolism or metabolism by the cytochrome P450 enzyme, it does undergo some metabolism by other means, themetabolic pathways of which includeoxidation andconjugation.[9][8] The precise enzymes responsible fortransformation of cetirizine have not been identified.[9]
Cetirizine iseliminated approximately 70 to 85% in theurine and 10 to 13% in thefeces.[9] In total, about 60% of cetirizine eliminated in the urine is unchanged.[9][8] It is eliminated in the urine via anactive transport mechanism.[8] Theelimination half-life of cetirizine ranges from 6.5 to 10 hours in healthy adults, with a mean across studies of approximately 8.3 hours.[9][8] The elimination half-life of cetirizine is increased in the elderly (to 12 hours), inhepatic impairment (to 14 hours), and inrenal impairment (to 20 hours).[8] Concentrations of cetirizine in the skin decline much slower than concentrations in the blood plasma.[8] Itsduration of action is at least 24 hours.[8]
Cetirizine containsL- andD-stereoisomers. Chemically, levocetirizine is the activeL-enantiomer of cetirizine. The drug is a member of thediphenylmethylpiperazine group of antihistamines.Analogues includecyclizine and hydroxyzine.[47]
The 1-(4-chlorophenylmethyl)-piperazine is alkylated with methyl (2-chloroethoxy)-acetate in the presence of sodium carbonate and xylene solvent to produce the Sn2 substitution product in 28% yield. Saponification of the acetate ester is done by refluxing with potassium hydroxide in absolute ethanol to afford a 56% yield of the potassium salt intermediate. This is then hydrolyzed with aqueous HCl and extracted to give an 81% yield of the carboxylic acid product.[48]
Cetirizine is available without a prescription.[49] In some countries, it is only available over-the-counter in packages containing seven or ten 10 mg doses.[50][51]
Cetirizine is available as acombination medication withpseudoephedrine, adecongestant.[52] The combination is often marketed using the same brand name as the cetirizine with a "-D" suffix (for example,Zyrtec-D).[53][54]
Cetirizine is sold under various brand names including Allacan, Benadryl Allergy, Piriteze Allergy, Quzyttir, and Zirtek Allergy.[55][56]
{{cite book}}: CS1 maint: location missing publisher (link)The equivalent dose of 60 mg cetirizine is also the highest dose ever administered in healthy subjects [13].
[...] 30 mg of hydroxyzine equals about 10 mg cetirizine [11] [...]
