Cetirizine

Cetirizine is an antihistamine available in multiple products and formulations, each with specific approved uses:

• Oral tablets, capsules, and oral solutions (multiple brands) temporarily relieve hay fever and upper respiratory allergy symptoms: runny nose, sneezing, itchy or watery eyes, and itching of the nose or throat
• Cetirizine Hydrochloride Oral Solution is indicated for perennial allergic rhinitis (year-round allergies from dust mites, animal dander, or mold) in children 6 to 23 months of age
• Cetirizine Hydrochloride Oral Solution is indicated for chronic idiopathic urticaria (persistent hives of unknown cause) in children 6 months to 5 years of age
• Quzyttir (intravenous cetirizine) is indicated for the treatment of acute urticaria (sudden hives) in adults and children 6 months of age and older, administered in a medical setting
• Zerviate (cetirizine ophthalmic solution 0.24%) is indicated for eye itching associated with allergic conjunctivitis, applied directly to the eyes

Cetirizine blocks H1 receptors — the sites on cells that histamine binds to when your immune system detects an allergen. By occupying these receptors, cetirizine prevents histamine from triggering the familiar allergy cascade: the sneezing, itching, runny nose, and hives. Importantly, cetirizine has very little activity in the brain compared to older antihistamines, which is why it tends to be less sedating — though drowsiness can still happen.

Studies show cetirizine also helps suppress the later phase of allergic inflammation, including the recruitment of immune cells like eosinophils and basophils after allergen exposure. Its effects last at least 24 hours at standard doses, and tolerance (the drug becoming less effective over time) was not observed in studies up to 35 days in children.

Oral forms of cetirizine are generally taken once daily and can be taken with or without food — food doesn't affect how much is absorbed, though it may slightly delay how quickly you feel the effect. Cetirizine Hydrochloride Oral Solution may be given once daily or split into two doses depending on the child's age, as directed by a doctor.

• Quzyttir (intravenous) is given by a healthcare professional once every 24 hours as needed for acute hives — always in a clinical setting
• Zerviate eye drops are applied directly to the eye per your prescriber's instructions
• Always follow the directions on your specific product label or as directed by your prescriber — do not adjust doses on your own

Most people tolerate cetirizine well; the most commonly reported side effects include:

• Drowsiness or sleepiness
• Headache
• Dry mouth
• Abdominal pain or stomach upset
• Nausea or vomiting
• Diarrhea
• Fatigue or malaise
• Sore throat

Serious but rare reactions reported after cetirizine use include seizures, hallucinations, severe allergic reactions (anaphylaxis), liver inflammation, and severe low blood pressure. If you experience any of these, stop the medication and seek medical help right away. A small number of people have also reported new-onset itching after stopping cetirizine following long-term use.

• Drowsiness and impaired alertness: Cetirizine can cause sedation. Avoid driving or operating heavy machinery until you know how it affects you. Never combine it with alcohol, sedatives, or tranquilizers — the effect multiplies.
• Kidney and liver disease: Cetirizine is cleared mainly by the kidneys. If your kidney or liver function is reduced, it can build up in your body — talk to your doctor before use. Quzyttir is not recommended in children under 6 years old with impaired kidney or liver function.
• Rare but serious post-marketing events: These include seizures, hallucinations, severe hypotension (very low blood pressure), liver inflammation, hemolytic anemia (breakdown of red blood cells), and suicidal thoughts. Though uncommon, these are real and warrant immediate medical attention.
• Discontinuation itching: Some people experience new itching within a few days of stopping cetirizine after long-term use. Speak with your doctor before stopping if you've been using it for months or longer.

Cetirizine has few major drug interactions, but a few combinations deserve attention:

• Alcohol: Increases drowsiness and reduces mental sharpness — avoid while taking cetirizine
• Sedatives, tranquilizers, and CNS depressants: Combining these with cetirizine can significantly amplify sedation and impair your ability to function safely
• Theophylline (at higher doses): May reduce how quickly cetirizine is cleared from your body, potentially increasing its effects — let your doctor know if you take this medication

This is not a complete list of interactions. Always talk with your doctor or pharmacist before starting, stopping, or changing any medication.

• Do not use if you are allergic to cetirizine, hydroxyzine, levocetirizine, or any ingredient in the product
• Tell your doctor if you have kidney disease — cetirizine clears through the kidneys and may accumulate
• Tell your doctor if you have liver disease — monitor for increased side effects
• Quzyttir should not be used in children under 6 years of age who have impaired kidney or liver function
• Safety and effectiveness in children under 6 months of age have not been established
• If you are pregnant, ask a health professional before use — there are no adequate controlled studies in pregnant women
• Cetirizine passes into breast milk; breastfeeding is not recommended while using cetirizine
• Older adults may process cetirizine more slowly (due to reduced kidney function) and may be more sensitive to side effects like drowsiness
• Tell your doctor or pharmacist about all sedatives or tranquilizers you take before starting cetirizine

Taking too much cetirizine can cause significant drowsiness in adults; in young children, it may cause restlessness and irritability followed by drowsiness. There is no specific antidote — treatment focuses on supportive care based on symptoms. If you suspect an overdose, call Poison Control at 1-800-222-1222 or seek emergency medical help right away.

Cetirizine strongly inhibits the skin's wheal-and-flare reaction (the red bump and surrounding redness) caused by histamine, with this effect lasting at least 24 hours at standard doses. Studies in people with cold-induced hives showed it also blocked responses to cold triggers, and in mildly asthmatic subjects, it blocked airway narrowing caused by inhaled histamine. Cetirizine also suppresses the later wave of allergic inflammation — reducing the influx of immune cells like eosinophils and basophils after allergen exposure.

When taken by mouth, cetirizine is absorbed quickly, reaching peak levels in the blood within about one hour; food doesn't reduce the total amount absorbed but can delay that peak by about 1.7 hours. Its average half-life (time for the body to clear half the drug) is about 8.3 hours in healthy adults, though this extends significantly in older adults and people with reduced kidney function. Cetirizine is about 93% bound to plasma proteins and is excreted primarily through the urine — roughly 50% as unchanged drug. Children clear cetirizine considerably faster than adults on a weight-adjusted basis, meaning younger patients may need proportionally different dosing.

Store at 20° to 25°C (68° to 77°F) excursions permitted to 15° to 30°C (59° to 86°F) ; or Store refrigerated, 2° to 8°C (36° to 46°F).