Cetirizine – the active substance of the drug Zyrtec – is a metabolite of hydroxyzine. It belongs to the group of competitive histamine antagonists and blocks H1-histamine receptors.
Zyrtec prevents development and facilitates the course of allergic reactions. It has antipruritic and anti exudative effects. Cetirizine affects the early histamine-dependent stage of allergic reactions. This drug contributes to the limit in the release of inflammatory mediators in the late stage of an allergic reaction. It also reduces the migration of eosinophils, neutrophils, and basophils. It stabilizes mast cell membranes. Zyrtec reduces capillary permeability, prevents the development of tissue edema, relieves spasm of smooth muscles. It eliminates the skin reaction to the introduction of histamine, specific allergens, as well as cooling (with cold urticaria). It reduces histamine-induced bronchoconstriction in mild asthma.
Cetirizine does not have an anticholinergic and anti serotonin effect. In therapeutic doses, the drug practically does not cause a sedative effect. After taking a single Zyrtec dose of 10 mg, its effect develops after 20 minutes (in 50% of patients), after 60 minutes (in 95% of patients). The duration lasts more than 24 hours. On the background of course treatment, tolerance to the antihistamine action of cetirizine does not develop. After therapy discontinuation, the effect lasts up to 3 days.
- Treatment of symptoms of year-round and seasonal allergic rhinitis and allergic conjunctivitis (such as itching, sneezing, nasal congestion, rhinorrhea, lacrimation, conjunctival hyperemia);
- Hay fever (hay fever);
- Allergic dermatoses, including atopic dermatitis, accompanied by itching and rashes.
Dosage and administration
- Children over 6 years old and adults: the initial dose is 5 mg (1/2 tablet or 10 drops) 1 time per day, if necessary, you can increase the dose to 10 mg (1 tablet or 20 drops) 1 time per day. Sometimes an initial dose of 5 mg (1/2 tablet or 10 drops) may be sufficient to achieve a therapeutic effect. The daily dose is 10 mg (1 tablet or 20 drops).
- Children from 6 to 12 months: 2.5 mg (5 drops) 1 time per day.
- Children from 1 year to 2 years: 2.5 mg (5 drops) up to 2 times a day.
- Children from 2 to 6 years: 2.5 mg (5 drops) 2 times a day or 5 mg (10 drops) 1 time per day.
- In patients with renal failure, the dose decreases depending on the creatinine clearance: with Cl creatinine 30–49 ml/min – 5 mg once a day, with 10–29 ml/min – 5 mg every other day.
For all dosage forms, there are the following contraindications:
- hypersensitivity to cetirizine, hydroxyzine or piperazine derivatives, as well as other components of the drug;
- end-stage renal failure (Cl creatinine 10 ml/min, dosage adjustment is required);
- advanced age (possibly a decrease in glomerular filtration);
- epilepsy and patients with increased convulsive readiness;
- patients with predisposing factors for urinary retention.
For film-coated tablets, there are additional contraindications:
- hereditary galactose intolerance, lack of lactase or glucose-galactose malabsorption syndrome;
- children under 6 years old.
- Immune system: rarely – hypersensitivity reactions; very rarely – anaphylactic shock.
- Nervous system: often – headache, fatigue, dizziness, drowsiness; infrequently – paresthesia; rarely – cramps; very rarely – taste perversion, dyskinesia, dystonia, fainting, tremor, tic; frequency unknown – memory impairment, incl. amnesia.
- Psychiatric disorders: infrequently – agitation; rarely – aggression, confusion, depression, hallucinations, sleep disturbance; frequency unknown – suicidal ideation.
- The organ of vision: very rarely – a violation of accommodation, blurred vision, nystagmus.
- The organ of hearing: the frequency is unknown – vertigo.
- Digestive system: often – dry mouth, nausea; infrequently – diarrhea, abdominal pain.
- CCC: rarely – tachycardia.
- Respiratory system: often – rhinitis, pharyngitis.
- Metabolic system: rarely – weight gain.
- Urinary system: very rarely – dysuria, enuresis; frequency unknown – urinary retention.
- Laboratory indicators: rarely – a change in functional liver samples (increased activity of hepatic transaminases, alkaline phosphatase, GGT, and bilirubin concentration); very rarely – thrombocytopenia.
- Skin: infrequently – rash, itching; rarely – urticaria; very rarely – angioedema, persistent erythema.
- General disorders: infrequently – asthenia, malaise; rarely – peripheral edema; frequency unknown – increased appetite.
- When studying the drug interaction of cetirizine with pseudoephedrine, cimetidine, ketoconazole, erythromycin, azithromycin, diazepam, glipizide and antipyrine, no clinically significant adverse interactions were detected.
- With simultaneous use with theophylline (400 mg/day), the total clearance of cetirizine is reduced by 16%.
- With simultaneous use with ritonavir, AUC of cetirizine increased by 40%, while a similar indicator of ritonavir slightly changed (−11%).
- With simultaneous use with macrolides (azithromycin, erythromycin) and ketoconazole, no ECG changes were observed.
- When using the drug in therapeutic doses, no data were obtained on interaction with alcohol (at a blood alcohol concentration of 0.5 g / l). Nevertheless, one should refrain from drinking alcohol during drug therapy in order to avoid CNS suppression.
- Before prescribing allergological tests, a 3-day “washing” period is recommended due to the fact that H1-histamine receptors block the development of allergic skin reactions.