Generic Name: Cetirizine (multiple generics available)
Common Brand Name: Zyrtec (Pfizer Labs – U.S.)
Popularity: 34th most commonly prescribed drug between 2002-2009 (U.S.)
Class: antihistamine, H1-receptor antagonist
Treatment Uses — For reduction of symptoms associated with perennial and/or seasonal allergic rhinitis. Reduces symptoms associated with pollen induced asthma (in conjunction with asthma meds).
Provides symptom relief in atopic (allergic) eczema. Effective for uncomplicated skin manifestations of chronic idiopathic urticaria. A small number of studies show cetirizine may be effective treatment for allergic cough in children exposed to pollen. May lower the incidence of pregnancy related nausea and vomiting.
There is one case report of cetirizine use to decrease gastrointestinal symptoms of an egg allergy. May be effective against cold urticaria symptoms, especially when used with other meds. Ineffective in preventing motion sickness or preventing drug induced rash from antiretroviral HIV treatments.
Cetirizine is one of four second-generation antihistamines available in the U.S. The other three are fexofenadine, astemizole, and loratadine. For a complete discussion of antihistamines, see the earlier Drug Whys column on fexofenadine.
From a selection perspective, cetirizine is the only of the four second-generation antihistamines often associated with side effects of sedation, dry mouth and urinary retention. All four have once daily dosing schedules. Astemizole has been associated with torsades de pointes, a lethal cardiac arrhythmia. Onset of action for astemizole is longest (five days) versus the other three agents (1 to 4 hours).
Dosing and Administration — The recommended dose of cetirizine in adults and children aged 6 and older is 5 to 10 milligrams, taken orally once daily. For children between the ages of 2 and 5, dosing is recommended at 2.5 to 5 milligrams orally, once daily or 2.5 milligrams twice daily.
For children from 6 to 23 months old, dosing is recommended at 2.5 milligrams orally, given once daily. For children ages 12 months to 23 months, the dose can be increased to a maximum of 5 milligrams daily, given as 2.5 milligrams twice each day.
Dosing for all ages depends on symptom severity. Some patients will respond nicely to lower doses, others may require higher doses. Some adults require up to 20 milligrams daily for adequate symptom relief. There are some small studies that suggest continuous treatment with cetirizine provides better symptom relief than demand treatment (dosing only when symptoms are present). Additional studies are needed to confirm this.
Food has no effect on absorption of cetirizine however the time to maximum concentration in the blood is delayed by 1.7 hours and decreased by 23 percent when taken with food.
In patients with moderate renal impairment, the clearance of cetirizine decreases by 70 percent. Dosing in patients with moderate to severe renal insufficiency (creatinine clearance less than 31 milliliters per minute) should be reduced to 5 milligrams daily (adults and children over 6 years old).
Cetirizine is not completely removed by hemodialysis but is altered, reducing its clearance by 70 percent. For patients on dialysis, a 5 milligram dose given three times a week just prior to the start of dialysis was found safe and quite effective in reducing pruritus (chronic itching).
Clearance in patients with hepatic insufficiency decreases by 40 percent and dosing in this population should also be limited to 5 milligrams daily. Cetirizine should not be used in children under 6 with renal or hepatic impairment. The manufacturer also recommends 5 milligram daily dosing for patients aged 77 and older based on an observed 40 percent reduction in clearance.
Overdoses of cetirizine have been reported. Somnolence has been the primary symptom. An adult overdose of 150 milligrams had no other clinical signs or symptoms. A pediatric (18 month) overdose of 180 milligrams experienced restlessness and irritability initially, followed by drowsiness. Citirizine is not effectively removed by dialysis. Lethal doses in mice are 237 milligrams per kilogram; in rats, 562 milligrams per kilogram.
Pharmacology/Pharmacokinetics/Stability – Following oral administration, initial antihistaminic activity is observed in 20 minutes with a peak response in 1 hour and duration of activity of 24 hours.
The kidneys excrete 60 percent of cetirizine within the first 24 hours and an additional 10 percent over the next four days. Ten percent of each dose is excreted in the feces. Elimination is significantly impaired in patients with liver or kidney dysfunction.
The number of women worldwide who have taken cetirizine during pregnancy is too small to completely rule out fetal risk. The low molecular weight of cetirizine makes it highly likely to cross the placental barrier during pregnancy.
Cetirizine is an active metabolite of hydoxyzine (a first generation antihistamine), which is generally considered safe for use during pregnancy. Cetirizine would not be anticipated to cause harm either.
Observational studies of women who have taken cetirizine have not discovered any differences in rates of malformations or other problems compared to control groups. Cetirizine is excreted in human breast milk; the potential for adverse effects to the infant are unknown. Animal studies would suggest there is minimal infant risk when taken by breastfeeding mothers.
Cetirizine is a potent H1-receptor antagonist or antihistamine. This means its mechanism of action is to inhibit histamine release from mast cells. It is less lipophilic than first generation antihistamines, which means it is far less likely to cross the blood-brain barrier to produce CNS effects (like sedation).
Cetirizine comes in 5 and 10 milligram tablets, chewable tablets and in a liquid syrup formulation concentrated at 1 milligram per milliliter. A cetirizine nasal spray formulation was available in the past but is no longer manufactured. Tablet colors and sizes vary by manufacturer.
Cetirizine is also marketed as a combination product, often mixed with the decongestant pseudoephedrine. Cetirizine tablets should be stored at room temperature (between 68 and 77 F) with excursions permitted between 59 to 86 F.
Cautions and Warnings — Patients should be cautioned about the potential for somnolence. Activities that require mental alertness such as operating heavy machinery or driving should be limited until individual effects of cetirizine are ascertained.
Important Side Effects and Interactions – The most common treatment-related adverse effects are somnolence (13.7 percent), fatigue (5.9 percent), headache (7.5 percent), and dry mouth (5 percent).
Clinical trials have shown that sedation may be dose dependent. In one study, sedation occurred in 23 percent and 25 percent of patients receiving cetirizine 10 milligrams and 20 mg, respectively, as opposed to 9 percent and 6 percent of patients receiving cetirizine 5 mg and placebo, respectively.
Currently, there is one drug reported to interact with cetirizine (ritonavir, a protease inhibitor most often used in treatment of HIV infection). This interaction is insignificant to prehospital and emergency medicine providers.
Average Costs — U.S.
• 5 and 10 milligram mg tablet (generic)*
Patient cost: $0.XX each
Large Hospital cost: $0.06 each (either strength)
*Wal Mart® and Target don’t include this med in their $4/month programs
References:
1. MICROMEDEX® Healthcare Series: Thomson Micromedex, Greenwood Village, Colorado (accessed March, 2011).
2. Albany Medical Center Pharmacy, Albany, New York.
