• Cetirizine may be used to treat the symptoms of an allergic reaction or insect bite.
• Cetirizine works selectively on peripheral histamine-1 (H-1) receptors (these are histamine receptors that are located outside of the brain and spinal cord) to block the effects of histamine. Histamine is a chemical that is released by mast cells in response to an allergen, and it is responsible for many of the symptoms of an allergic reaction, such as swelling of the mucous membranes, sneezing, and itching. Cetirizine binds to histamine receptors and prevents histamine from having an effect on those receptors, which reduces the symptoms of an allergic reaction. Because it acts on peripheral histamine receptors, cetirizine is much less likely to cause drowsiness compared with some older antihistamines.
• Cetirizine belongs to the group of drugs known as antihistamines. Cetirizine may also be called an H1-antihistamine, a second generation antihistamine, or a nonsedating antihistamine.

• Used to treat allergic-type reactions due to perennial or seasonal allergic rhinitis (hay fever).
• Effective at controlling symptoms such as sneezing, itching, watery eyes, and runny nose that occur as a result of other respiratory allergens.
• Can provide relief from itching that occurs as a result of chronic urticaria (hives). Symptoms of hives include raised, red, itchy bumps, streaks, or blotches on the skin.
• May be used in the treatment of allergic conjunctivitis, insect bites, and other allergic skin disorders.
• Is less likely to cause sedation than older antihistamines.
• Can be taken once a day. The dosage for adults and children over the age of 6 is one 10mg tablet once daily. 5mg may be appropriate for less severe symptoms.
• May be given daily on a regular basis when allergens are most prevalent (such as during spring or summer).
• Cetirizine has been demonstrated to be safe in children older than 6 months.
• No dosage adjustment is required in liver disease.
• An intravenous formulation is available called Quzyttir
• Available over-the-counter.
• Generic cetirizine is available.

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

• A headache, sore throat, abdominal pain, fatigue, drowsiness, or coughing. Other side effects are uncommon.
• Generally does not cause drowsiness, although more likely to do so at higher dosages. Caution should be exercised before driving or operating machinery until the full effects of cetirizine are known.
• The dosage of cetirizine should be reduced in kidney disease and caution should be exercised when cetirizine is used in people with seizure disorders.
• Cetirizine, like all other antihistamines, may decrease the response to skin prick tests. Discontinue cetirizine at least 72 hours prior to skin testing.
• Weigh up the risks versus benefits before using during pregnancy and breastfeeding.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

• May be taken with or without food. Cetirizine is usually taken once a day. During the pollen season, your doctor may advise you to take it every day if you suffer from seasonal allergic rhinitis.
• Although cetirizine is unlikely to make you drowsy, some people are susceptible to this effect, especially if they are taking dosages at the upper end of the recommended dosage range. Do not drive or operate machinery if cetirizine makes you drowsy. Alcohol and other sedative-like drugs may cause additional reductions in alertness if used with cetirizine.
• Seek urgent medical advice if you have hives and develop swelling of the face, throat, or tongue, dizziness, drooling, difficulty speaking, or shortness of breath.
• Cetirizine is not a substitute for epinephrine which is used for the treatment of severe allergies and anaphylaxis.
• Cetirizine is available as a suspension for adults and children who have difficulty swallowing tablets.
• See your doctor if your mild allergy symptoms have not improved after three days of treatment with cetirizine, or if your hives persist for more than six weeks despite taking cetirizine.
• Discontinue cetirizine once your allergy symptoms have resolved.
• Do not take cetirizine during pregnancy or while breastfeeding unless on the advice of your doctor.

• Peak concentrations are reached within one hour of administration of cetirizine tablets or syrup. The onset of effect occurs within 20 minutes in 50% of people and within an hour in 95%.
• Effects persist for at least 24 hours following a single dose of cetirizine. No tolerance has been found to cetirizine's antihistaminic effect. Once discontinued, the skin recovers its normal reactivity to histamine within three days.
• Taking 10mg of cetirizine is more effective than taking 5mg; taking 20mg appears not to provide any additional effect.
• Food has no effect on the overall absorption of cetirizine; however, it may increase the time it takes for peak levels of cetirizine to be reached in the blood.

Medicines that interact with cetirizine may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with cetirizine. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with cetirizine include:

• anticonvulsants, such as fosphenytoin, lamotrigine, levetiracetam, phenytoin, or valproic acid
• antidepressants, such as clomipramine, escitalopram, or fluvoxamine
• antipsychotics, such as aripiprazole, chlorpromazine, or clozapine
• baclofen
• barbituates, such as butabarbital
• benzodiazepines, such as diazepam or temazepam
• benztropine
• bupropion
• buspirone
• cannabis and cannabinoids
• clonidine
• HIV medications such as darunavir, lopinavir, ritonavir, or saquinavir
• duloxetine
• ketamine
• lithium
• monoamine oxidase antidepressants, such as phenelzine, isocarboxazid
• mumps skin test antigen
• opioids, such as codeine, fentanyl, hydrocodone
• other antihistamines, such as azatadine, azelastine, or brompheniramine
• sleeping medications, such as zolpidem
• St John's wort
• topiramate
• voriconazole.

Alcohol may increase the risk of sedation with cetirizine.

Note that this list is not all-inclusive and includes only common medications that may interact with cetirizine. You should refer to the prescribing information for cetirizine for a complete list of interactions.