{
  "id": "cetirizine",
  "title": "Cetirizine",
  "lang": "en",
  "source_lang": "en",
  "summary": "Cetirizine is a second-generation antihistamine used mainly for allergic rhinitis and chronic urticaria, sold as Zyrtec and other brands.",
  "category": "health",
  "subcategory": "drugs",
  "type": "concept",
  "aliases": [
    "Zyrtec",
    "Reactine",
    "cetirizine hydrochloride"
  ],
  "generated_at": "2026-10-15",
  "model": "pro/claude-haiku-5-5",
  "url": "https://aiwiki.page/en/cetirizine/",
  "translations": {
    "zh-Hans": {
      "url": "https://aiwiki.page/zh/cetirizine/",
      "json": "https://aiwiki.page/zh/cetirizine.json"
    }
  },
  "sections": [
    {
      "heading": "",
      "text": "Cetirizine is an oral second-generation antihistamine used to relieve symptoms of allergic rhinitis and chronic urticaria, two common allergic conditions. It is sold under the brand name Zyrtec and others, and it is taken by mouth. Its value lies in relieving allergy symptoms without the heavy sedation associated with earlier drugs in its class, and its chemistry has informed the design of later antihistamines."
    },
    {
      "heading": "Chemistry",
      "text": "Chemically, cetirizine is a pharmacological derivative of piperazine. It is a piperazine derivative and a metabolite of hydroxyzine, and it is a nonsedating, long-acting antihistamine with mast cell stabilizing activity. Its molecule is zwitterionic, meaning it carries both positive and negative charges at physiological pH. Cetirizine has one asymmetric carbon, so it can be resolved into enantiomers. The commercial drug is a chiral racemate: equal amounts of two enantiomers, levocetirizine and dextrocetirizine, which do not interconvert.\n\nHydroxyzine, an older antihistamine, is converted in the body into cetirizine, which accounts for most of the relevant antihistamine activity. The relationship makes cetirizine one of the best-known examples of a metabolite developed into a drug in its own right."
    },
    {
      "heading": "Mechanism of action",
      "text": "Cetirizine is a selective antagonist at histamine H1 receptors. It competes with histamine for binding sites on these receptors but does not activate them. Importantly, it does not stop the body from releasing histamine. Instead, it prevents released histamine from reaching its receptors. In vitro receptor binding studies have shown no detectable affinity for histamine receptors other than H1. Some sources note weaker interactions with muscarinic cholinergic and serotonin receptors, but in vivo and ex vivo animal models have shown insignificant anticholinergic and antiserotonergic effects.\n\nCetirizine also has effects beyond H1 blockade. It also possesses some mast cell stabilizing properties. Laboratory studies report that it inhibits the production of interleukin 8 (IL8) and leukotriene B4 (LTB4) by immune cells, two potent chemoattractants. The clinical importance of these anti-inflammatory effects is unsettled. Many antihistamines show anti-inflammatory actions independent of H1 blockade, and whether such effects matter in patients remains an open question, with much of the evidence coming from in vitro work.\n\nBrain penetration is low. Peak cetirizine concentrations in the brain are less than 10% of plasma concentrations. This limited passage across the brain barrier is the main basis for its reduced sedation compared with first-generation drugs."
    },
    {
      "heading": "Pharmacokinetics",
      "text": "Cetirizine is rapidly absorbed upon oral administration, and although food may slightly reduce the rate of absorption, the extent is not affected. In a labeling study, food delayed the time to peak concentration by about 1.7 hours and lowered the peak concentration by 23%. Bioavailability is above 70%, and protein binding is between 88 and 96%.\n\nMetabolism is limited. Metabolism is minimal and not mediated by cytochrome P450 enzymes. Most of the drug leaves through the kidney system, largely as unchanged drug in the urine. Because it is not heavily metabolized, the drug has relatively few interactions with other medicines. The mean elimination half-life across 146 healthy volunteers in multiple pharmacokinetic studies was 8.3 hours. Half-life is shorter in children, and adolescents, like adults, can usually take it once a day."
    },
    {
      "heading": "History and development",
      "text": "Cetirizine was developed in Belgium. The drug was marketed by the company UCB, which is also the originator of the drug, and/or Pfizer under the brand name Zyrtec. Sources disagree on the exact dates. One timeline gives a patent in 1983, approval in Europe in 1987, approval in the USA as a prescription drug in 1995, and approval as an OTC drug in the USA in 2007. Another encyclopedia entry gives a patent year of 1981 and first use in 1987. A commercial drug database lists Johnson & Johnson as originator, which conflicts with patent records that name UCB.\n\nCetirizine was later the basis for levocetirizine, the single active enantiomer. Researchers found that only the R-enantiomer was responsible for most antihistamine activity. Levocetirizine was launched in the first quarter of 2001 in Germany, followed by a pan-European launch. Its development is an example of chiral switching, a process in which the active enantiomer of an existing drug is isolated and marketed as a separate medication. Proponents argue that levocetirizine has a higher affinity and selectivity to H1 receptors than its racemate. A review, however, observed that the enantiomer was commercialized worldwide for a patent reason, and that most studies investigated levocetirizine without demonstrating a superiority, either in efficacy or in safety, compared to the racemic compound."
    },
    {
      "heading": "Clinical use",
      "text": "Cetirizine is indicated for the relief of symptoms associated with seasonal or perennial allergic rhinitis, as well as for the uncomplicated skin manifestations of chronic idiopathic urticaria in adults and children 6 months of age and older. Its efficacy in these conditions has been extensively studied. The drug is on the World Health Organization's List of Essential Medicines. Extended-release formulations are also sold in combination with the decongestant pseudoephedrine, a product whose adverse-effect profile includes insomnia, dry mouth, fatigue, and dizziness."
    },
    {
      "heading": "Adverse effects and safety",
      "text": "The most frequent adverse effects in adults are mild. Its primary adverse effects in adults include somnolence, fatigue, pharyngitis, dizziness, and dry mouth. Sleepiness appears to increase with dose. Somnolence appears to be a dose-related effect of cetirizine. Compared with placebo, dry mouth was found to be more frequent with cetirizine in clinical studies. In one controlled study of patients 12 years and older, insomnia occurred more frequently with cetirizine than with placebo (9 vs 5.3%, respectively).\n\nIn young children the picture differs somewhat. In a controlled study of 1 week's duration in patients 6-11 months of age, those receiving cetirizine exhibited greater irritability/fussiness than those receiving placebo. Children, in particular, are more likely than adults to experience headaches while taking cetirizine.\n\nSedation is reduced compared with older antihistamines but not absent. Research indicates that in some patients, cetirizine contributes to daytime sleepiness. For this reason, labeling advises due caution when driving a car or operating potentially dangerous machinery.\n\nPregnancy and breastfeeding are common concerns. One review presents the drug as the first choice for good safety data during pregnancy and breastfeeding. That assessment draws on observational data, including a study that searched the UCB Pharma Patient Safety Database for pregnancies up to 28 February 2015. Guidance for breastfeeding is more cautious: prolonged use of larger doses may cause a decrease in the milk supply or drowsiness and other adverse effects in the infant.\n\nRare reports also exist. One report described worsening of myasthenia with cetirizine, though the authors did not perform a re-challenge."
    },
    {
      "heading": "Regulatory status",
      "text": "Regulatory status varies by country. In the United States it is available both over the counter and by prescription, and in the United Kingdom it is on the general sales list, which allows OTC sale. Dosing and strength differ between products, and users in different countries should follow local labeling."
    }
  ],
  "links": [
    "antihistamine",
    "allergic-rhinitis",
    "urticaria",
    "allergy",
    "pharmacology",
    "chirality",
    "inflammation",
    "brain",
    "kidney",
    "medicine"
  ],
  "sources": [
    {
      "title": "Cetirizine",
      "url": "https://simple.m.wikipedia.org/wiki/Cetirizine"
    },
    {
      "title": "Cetirizine - an overview",
      "url": "https://www.sciencedirect.com/topics/immunology-and-microbiology/cetirizine"
    },
    {
      "title": "Process for making n-(diphenylmethyl)piperazines",
      "url": "https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/7989623"
    },
    {
      "title": "Focus on the cetirizine use in clinical practice: a reappraisal 30 years later",
      "url": "https://link.springer.com/article/10.1186/s40248-019-0203-6"
    },
    {
      "title": "What is the mechanism of Cetirizine Hydrochloride?",
      "url": "https://synapse.patsnap.com/article/what-is-the-mechanism-of-cetirizine-hydrochloride"
    },
    {
      "title": "Cetirizine: Uses, Interactions, Mechanism of Action",
      "url": "https://go.drugbank.com/drugs/DB00341"
    },
    {
      "title": "Cetirizine - Mechanism, Indication, Contraindications, Dosing, Adverse Effect, Interaction, Renal Dose, Hepatic Dose",
      "url": "https://www.pediatriconcall.com/drugs/cetirizine/394"
    },
    {
      "title": "The Effect of Levocetirizine on Inflammatory Mediators in Dermatographism",
      "url": "https://clinicaltrials.gov/study/NCT01008592"
    },
    {
      "title": "Methods for treating allergic disorders using optically pure (-) cetirizine",
      "url": "https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/5698558"
    },
    {
      "title": "Cetirizine",
      "url": "https://en.wikipedia.org/wiki/Cetirizine"
    },
    {
      "title": "Cetirizine: Package Insert / Prescribing Information",
      "url": "https://www.drugs.com/pro/cetirizine.html"
    },
    {
      "title": "Cetirizine use in childhood: an update of a friendly 30-year drug",
      "url": "https://link.springer.com/article/10.1186/s12948-020-00118-5"
    },
    {
      "title": "Levocetirizine vs Cetirizine: Differences, History, Mechanism and Which is Better - Pharmacist Notes",
      "url": "https://pharmacistnotes.com/histamine/levocetirizine-vs-cetirizine-difference-which-is-better/"
    },
    {
      "title": "Cetirizine Drug Intelligence — PatSnap Eureka",
      "url": "https://www.patsnap.com/resources/blog/ls-blog/cetirizine-drug-intelligence-patsnap-eureka/"
    },
    {
      "title": "Cetirizine - an overview",
      "url": "https://www.sciencedirect.com/topics/chemistry/cetirizine"
    },
    {
      "title": "Cetirizine: Definition, Mechanism of Action and Application - BOC Sciences",
      "url": "https://www.bocsci.com/resources/cetirizine-definition-mechanism-of-action-and-application.html"
    },
    {
      "title": "Cetirizine - StatPearls - NCBI Bookshelf - NIH",
      "url": "https://www.ncbi.nlm.nih.gov/sites/books/NBK549776/"
    },
    {
      "title": "Cetirizine",
      "url": "https://www.pharmacompass.com/chemistry-chemical-name/cetirizine"
    },
    {
      "title": "The anti-inflammatory effects of levocetirizine - are they clinically relevant or just an interesting additional effect?",
      "url": "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2804563/"
    },
    {
      "title": "Differential Regulation of Thermodynamic Binding Forces of Levocetirizine and (S)-Cetirizine by Lys191 in Human Histamine H1 Receptors",
      "url": "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6321019/"
    }
  ],
  "license": "https://creativecommons.org/licenses/by/4.0/"
}