Indications : Rhinitis, perennial allergic; Rhinitis, seasonal allergic; Urticaria, chronic Pregnancy Category B FDA Approved 1995 Dec DRUG CLASS : Antihistamines BRAND NAMES : Alercet (Colombia); Alerid (Bahrain, Cyprus, Egypt, Iran, Iraq, Jordan, Kuwait, Lebanon, Libya, Oman, Qatar, Republic-of-Yemen, Saudi-Arabia, Syria, United-Arab-Emirates); Cesta (Korea); Cetrine (Colombia); Cetrizet (Thailand); Cistamine (Thailand); Histazine (Israel); Nosemin (Korea); Reactine (Canada); Riztec (Indonesia); Ryzen (Indonesia); Sancotec (Korea); Selitex (Korea); Triz (India); Virlix (France, Portugal, Spain, Italy, Mexico, Philippines); Zeran (Benin, Burkina-Faso, Ethiopia, Gambia, Ghana, Guinea, Ivory-Coast, Kenya, Liberia, Malawi, Mali, Mauritania, Mauritius, Morocco, Niger, Nigeria, Senegal, Seychelles, Sierra-Leone, Sudan, Tanzania, Tunia, Uganda, Zambia, Zimbabwe); Zirtin (India); Zyrtec (US); Zyrzine (Thailand); (International brand names outside U.S. in italics) DESCRIPTION : Cetirizine HCl is an orally active and selective H1-receptor antagonist. The chemical name is (±) – [2- [4- [ (4-chlorophenyl)phenylmethyl] -1- piperazinyl] ethoxy]acetic acid, dihydrochloride. Cetirizine HCl is a racemic compound with an empirical formula of C21H25C1N2O3·2HCl. The molecular weight is 461.82. Cetirizine HCl is a white, crystalline powder and is water soluble. Zyrtec tablets are formulated as white, film-coated, rounded-off rectangular shaped tablets for oral administration and are available in 5 and 10 mg strengths. Inactive Ingredients: Lactose; magnesium stearate; povidone; titanium dioxide; hydroxypropyl methylcellulose; polyethylene glycol; and corn starch. Zyrtec syrup is a colorless to slightly yellow syrup containing cetirizine HCl at a concentration of 1 mg/ml (5 mg/5 ml) for oral administration. The pH is between 4 and 5. Inactive Ingredients: Banana flavor; glacial acetic acid; glycerin; grape flavor; methylparaben; propylene glycol; propylparaben; sodium acetate; sugar syrup; and water. CLINICAL PHARMACOLOGY : Mechanism of Action Cetirizine, a human metabolite of hydroxyzine, is an antihistamine; its principal effects are mediated via selective inhibition of peripheral H1 receptors. The antihistaminic activity of cetirizine has been clearly documented in a variety of animal and human models. In vivo and ex vivo animal models have shown negligible anticholinergic and antiserotonergic activity. In clinical studies, however, dry mouth was more common with cetirizine than with placebo. In vitro receptor binding studies have shown no measurable affinity for other than H1 receptors. Autoradiographic studies with radiolabeled cetirizine in the rat have shown negligible penetration into the brain. Ex vivo experiments in the mouse have shown that systemically administered cetirizine does not significantly occupy cerebral H1 receptors. Pharmacokinetics Absorption: Cetirizine was rapidly absorbed with a time to maximum concentration (Tmax) of approximately 1 hour following oral administration of tablets or syrup in adults. Comparable bioavailability was found between the tablet and syrup dosage forms. When healthy volunteers were administered multiple doses of cetirizine (10 mg tablets once daily for 10 days), a mean peak plasma concentration (Cmax) of 311 ng/ml was observed. No accumulation was observed. Cetirizine pharmacokinetics were linear for oral doses ranging from 5 to 60 mg. Food had no effect on the extent of cetirizine exposure (AUC) but Tmax was delayed by 1.7 hours and Cmax was decreased by 23% in the presence of food. Distribution : The mean plasma protein binding of cetirizine is 93%, independent of concentration in the range of 25-1000 ng/ml, which includes the therapeutic plasma levels observed. Metabolism : A mass balance study in 6 healthy male volunteers indicated that 70% of the administered radioactivity was recovered in the urine and 10% in the feces. Approximately 50% of the radioactivity was identified in the urine as unchanged drug. Most of the rapid increase in peak plasma radioactivity was associated with parent drug, suggesting a low degree of first-pass metabolism. Cetirizine is metabolized to a limited extent by oxidative O-dealkylation to a metabolite with negligible antihistaminic activity. The enzyme or enzymes responsible for this metabolism have not been identified. Elimination : The mean elimination half-life in 146 healthy volunteers across multiple pharmacokinetic studies was 8.3 hours and the apparent total body clearance for cetirizine was approximately 53 ml/min. Special Populations Pediatric Patients : When pediatric patients aged 7 to 12 years received a single, 5-mg oral cetirizine capsule, the mean Cmax was 275 ng/ml. Based on cross-study comparisons, the weight-normalized, apparent total body clearance was 33% greater and the elimination half-life was 33% shorter in this pediatric population than in adults. In pediatric patients aged 2 to 5 years who received 5 mg of cetirizine, the mean Cmax was 660 ng/ml. Based on cross-study comparisons, the weight-normalized apparent total body clearance was 81 to 111% greater and the elimination half-life was 33 to 41% shorter in this pediatric population than in adults. Geriatric Patients : Following a single, 10-mg oral dose, the elimination half-life was prolonged by 50% and the apparent total body clearance was 40% lower in 16 geriatric subjects with a mean age of 77 years compared to 14 adult subjects with a mean age of 53 years. The decrease in cetirizine clearance in these elderly volunteers may be related to decreased renal function. Effect of Gender : The effect of gender on cetirizine pharmacokinetics has not been adequately studied. Effect of Race: No race-related differences in the kinetics of cetirizine have been observed. Renal Impairment : The kinetics of cetirizine were studied following multiple, oral, 10-mg daily doses of cetirizine for 7 days in 7 normal volunteers (creatinine clearance 89-128 ml/min), 8 patients with mild renal function impairment (creatinine clearance 42-77 ml/min) and 7 patients with moderate renal function impairment (creatinine clearance 11-31 ml/min). The pharmacokinetics of cetirizine were similar in patients with mild impairment and normal volunteers. Moderately impaired patients had a 3-fold increase in half-life and a 70% decrease in clearance compared to normal volunteers. Patients on hemodialysis (n=5) given a single, 10-mg dose of cetirizine had a 3-fold increase in half-life and a 70% decrease in clearance compared to normal volunteers. Less than 10% of the administered dose was removed during the single dialysis session. Dosing adjustment is necessary in patients with moderate or severe renal impairment and in patients on dialysis (see DOSAGE AND ADMINISTRATION). Hepatic Impairment : Sixteen patients with chronic liver diseases (hepatocellular, cholestatic, and biliary cirrhosis), given 10 or 20 mg of cetirizine as a single, oral dose had a 50% increase in half-life along with a corresponding 40% decrease in clearance compared to 16 healthy subjects. Dosing adjustment may be necessary in patients with hepatic impairment (see DOSAGE AND ADMINISTRATION). Pharmacodynamics Studies in 69 adult normal volunteers (aged 20 to 61 years) showed that cetirizine at doses of 5 and 10 mg strongly inhibited the skin wheal and flare caused by the intradermal injection of histamine. The onset of this activity after a single 10-mg dose occurred within 20 minutes in 50% of subjects and within one hour in 95% of subjects; this activity persisted for at least 24 hours. Cetirizine at doses of 5 and 10 mg also strongly inhibited the wheal and flare caused by intradermal injection of histamine in 19 pediatric volunteers (aged 5 to 12 years) and the activity persisted for at least 24 hours. In a 35-day study in children aged 5 to 12, no tolerance to the antihistaminic (suppression of wheal and flare response) effects of cetirizine was found. The effects of intradermal injection of various other mediators or histamine releasers were also inhibited by cetirizine, as was response to a cold challenge in patients with cold-induced urticaria. In mildly asthmatic subjects, cetirizine at 5 to 20 mg blocked bronchoconstriction due to nebulized histamine, with virtually total blockade after a 20-mg dose. In studies conducted for up to 12 hours following cutaneous antigen challenge, the late phase recruitment of eosinophils, neutrophils and basophils, components of the allergic inflammatory response, was inhibited by cetirizine at a dose of 20 mg. In four clinical studies in healthy adult males, no clinically significant mean increases in QTc were observed in cetirizine treated subjects. In the first study, a placebo-controlled crossover trial, cetirizine was given at doses up to 60 mg per day, 6 times the maximum clinical dose, for 1 week, and no significant mean QTc prolongation occurred. In the second study, a crossover trial, cetirizine 20 mg and erythromycin (500 mg every 8 hours) were given alone and in combination. There was no significant effect on QTc with the combination or with cetirizine alone. In the third trial, also a crossover study, cetirizine 20 mg and ketoconazole (400 mg per day) were given alone and in combination. Cetirizine caused a mean increase in QTc of 9.1 msec from baseline after 10 days of therapy. Ketoconazole also increased QTc by 8.3 msec. The combination caused an increase of 17.4 msec, equal to the sum of the individual effects. Thus, there was no significant drug interaction on QTc with the combination of cetirizine and ketoconazole. In the fourth study, a placebo-controlled parallel trial, cetirizine 20 mg was given alone or in combination with azithromycin (500 mg as a single dose on the first day followed by 250 mg once daily). There was no significant increase in QTc with cetirizine 20 mg alone or in combination with azithromycin. In a four-week clinical trial in pediatric patients aged 6 to 11 years, results of randomly obtained ECG measurements before treatment and after 2 weeks of treatment showed that cetirizine 5 or 10 mg did not significantly increase QTc versus placebo. The effects of cetirizine on the QTc interval at doses higher than the 10 mg dose have not been studied in children less than 12 years of age. The effect of cetirizine on the QTc interval in children less than 6 years of age has not been studied. In a six-week, placebo-controlled study of 186 patients (aged 12 to 64 years) with allergic rhinitis and mild to moderate asthma, cetirizine 10 mg once daily improved rhinitis symptoms and did not alter pulmonary function. In a two-week, placebo-controlled clinical trial, a subset analysis of 65 pediatric (aged 6 to 11 years) allergic rhinitis patients with asthma showed cetirizine did not alter pulmonary function. These studies support the safety of administering cetirizine to pediatric and adult allergic rhinitis patients with mild to moderate asthma. CLINICAL STUDIES : Nine multicenter, randomized, double-blind, clinical trials comparing cetirizine 5 to 20 mg to placebo in patients 12 years and older with seasonal or perennial allergic rhinitis were conducted in the United States. Five of these showed significant reductions in symptoms of allergic rhinitis, 3 in seasonal allergic rhinitis (1 to 4 weeks in duration) and 2 in perennial allergic rhinitis for up to 8 weeks in duration. Two 4-week multicenter, randomized, double-blind, clinical trials comparing cetirizine 5 to 20 mg to placebo in patients with chronic idiopathic urticaria were also conducted and showed significant improvement in symptoms of chronic idiopathic urticaria. In general, the 10-mg dose was more effective than the 5-mg dose and the 20-mg dose gave no added effect. Some of these trials included pediatric patients aged 12 to 16 years. In addition, four multicenter, randomized, placebo-controlled, double-blind 2-4 week trials in 534 pediatric patients aged 6 to 11 years with seasonal allergic rhinitis were conducted in the United States at doses up to 10 mg. INDICATIONS AND USAGE : Seasonal Allergic Rhinitis: Cetirizine is indicated for the relief of symptoms associated with seasonal allergic rhinitis due to allergens such as ragweed, grass and tree pollens in adults and children 2 years of age and older. Symptoms treated effectively include sneezing, rhinorrhea, nasal pruritus, ocular pruritus, tearing, and redness of the eyes. Perennial Allergic Rhinitis: Cetirizine is indicated for the relief of symptoms associated with perennial allergic rhinitis due to allergens such as dust mites, animal dander and molds in adults and children 2 years of age and older. Symptoms treated effectively include sneezing, rhinorrhea, postnasal discharge, nasal pruritus, ocular pruritus, and tearing. Chronic Urticaria: Cetirizine is indicated for the treatment of the uncomplicated skin manifestations of chronic idiopathic urticaria in adults and children 2 years of age and older. It significantly reduces the occurrence, severity, and duration of hives and significantly reduces pruritus. CONTRAINDICATIONS : Cetirizine is contraindicated in those patients with a known hypersensitivity to it or any of its ingredients or hydroxyzine. PRECAUTIONS : Activities Requiring Mental Alertness : In clinical trials, the occurrence of somnolence has been reported in some patients taking cetirizine; due caution should therefore be exercised when driving a car or operating potentially dangerous machinery. Concurrent use of cetirizine with alcohol or other CNS depressants should be avoided because additional reductions in alertness and additional impairment of CNS performance may occur. Carcinogenesis, Mutagenesis, and Impairment of Fertility : In a 2-year carcinogenicity study in rats, cetirizine was not carcinogenic at dietary doses up to 20 mg/kg (approximately 15 times the maximum recommended daily oral dose in adults on a mg/m2 basis, or approximately 10 times the maximum recommended daily oral dose in children on a mg/m2 basis). In a 2-year carcinogenicity study in mice, cetirizine caused an increased incidence of benign liver tumors in males at a dietary dose of 16 mg/kg (approximately 6 times the maximum recommended daily oral dose in adults on a mg/m2 basis, or approximately 4 times the maximum recommended daily oral dose in children on a mg/m2 basis). No increase in the incidence of liver tumors was observed in mice at a dietary dose of 4 mg/kg (approximately 2 times the maximum recommended daily oral dose in adults on a mg/m2 basis, or approximately equal to the maximum recommended daily oral dose in children on a mg/m2 basis). The clinical significance of these findings during long-term use of cetirizine is not known. Cetirizine was not mutagenic in the Ames test, and not clastogenic in the human lymphocyte assay, the mouse lymphoma assay, and in vivo micronucleus test in rats. In a fertility and general reproductive performance study in mice, cetirizine did not impair fertility at an oral dose of 64 mg/kg (approximately 25 times the maximum recommended daily oral dose in adults on a mg/m2 basis). Pregnancy Category B : In mice, rats, and rabbits, cetirizine was not teratogenic at oral doses up to 96, 225, and 135 mg/kg, respectively (approximately 40, 180 and 220 times the maximum recommended daily oral dose in adults on a mg/m2 basis). There are no adequate and well-controlled studies in pregnant women. Because animal studies are not always predictive of human response, cetirizine should be used in pregnancy only if clearly needed. Nursing Mothers : In mice, cetirizine caused retarded pup weight gain during lactation at an oral dose in dams of 96 mg/kg (approximately 40 times the maximum recommended daily oral dose in adults on a mg/m2 basis). Studies in beagle dogs indicated that approximately 3% of the dose was excreted in milk. Cetirizine has been reported to be excreted in human breast milk. Because many drugs are excreted in human milk, use of cetirizine in nursing mothers is not recommended. Geriatric Use : In placebo-controlled trials, 186 patients aged 65 to 94 years received doses of 5 to 20 mg of cetirizine per day. Adverse events were similar in this group to patients under age 65. Subset analysis of efficacy in this group was not done. Pediatric Use : The safety of cetirizine, at daily doses of 5 or 10 mg, has been demonstrated in 376 pediatric patients aged 6 to 11 years in placebo-controlled trials lasting up to four weeks and in 254 patients in a non-placebo-controlled 12-week trial. The safety of cetirizine has been demonstrated in 168 patients aged 2 to 5 years in placebo-controlled trials of up to 4 weeks duration. On a mg/kg basis, most of the 168 patients received between 0.2 and 0.4 mg/kg of cetirizine HCl. The effectiveness of cetirizine for the treatment of seasonal and perennial allergic rhinitis and chronic idiopathic urticaria in pediatric patients aged 2 to 11 years is based on an extrapolation of the demonstrated efficacy of cetirizine in adults in these conditions and the likelihood that the disease course, pathophysiology and the drug’s effect are substantially similar between these two populations. The recommended doses for the pediatric population are based on cross-study comparisons of the pharmacokinetics and pharmacodynamics of cetirizine in adult and pediatric subjects and on the safety profile of cetirizine in both adult and pediatric patients at doses equal to or higher than the recommended doses. The cetirizine AUC and Cmax in pediatric subjects aged 2 to 5 years who received a single dose of 5 mg of cetirizine syrup and in pediatric subjects aged 6 to 11 years who received a single dose of 10 mg of cetirizine syrup were estimated to be intermediate between that observed in adults who received a single dose of 10 mg of cetirizine tablets and those who received a single dose of 20 mg of cetirizine tablets. The safety and effectiveness of cetirizine in pediatric patients under the age of 2 years have not yet been established. DRUG INTERACTIONS : Pharmacokinetic interaction studies with cetirizine in adults were conducted with pseudoephedrine, antipyrine, ketoconazole, erythromycin and azithromycin. No interactions were observed. In a multiple dose study of theophylline (400 mg once daily for 3 days) and cetirizine (20 mg once daily for 3 days), a 16% decrease in the clearance of cetirizine was observed. The disposition of theophylline was not altered by concomitant cetirizine administration. Drug-Drug Interactions: No clinically significant drug interactions have been found with theophylline at a low dose, azithromycin, pseudoephedrine, ketoconazole, or erythromycin. There was a small decrease in the clearance of cetirizine caused by a 400-mg dose of theophylline; it is possible that larger theophylline doses could have a greater effect. ADVERSE REACTIONS : Controlled and uncontrolled clinical trials conducted in the United States and Canada included more than 6000 patients aged 12 years and older, with more than 3900 receiving cetirizine at doses of 5 to 20 mg per day. The duration of treatment ranged from 1 week to 6 months, with a mean exposure of 30 days. Most adverse reactions reported during therapy with cetirizine were mild or moderate. In placebo-controlled trials, the incidence of discontinuations due to adverse reactions in patients receiving cetirizine 5 or 10 mg was not significantly different from placebo (2.9% vs. 2.4%, respectively). The most common adverse reaction in patients aged 12 years and older that occurred more frequently on cetirizine than placebo was somnolence. The incidence of somnolence associated with cetirizine was dose related, 6% in placebo, 11% at 5 mg and 14% at 10 mg. Discontinuations due to somnolence for cetirizine were uncommon (1.0% on cetirizine vs. 0.6% on placebo). Fatigue and dry mouth also appeared to be treatment-related adverse reactions. There were no differences by age, race, gender or by body weight with regard to the incidence of adverse reactions. TABLE 1 lists adverse experiences in patients aged 12 years and older which were reported for cetirizine 5 and 10 mg in controlled clinical trials in the United States and that were more common with cetirizine than placebo. TABLE 1 Adverse Experiences Reported in Patients Aged 12 Years and Older in Placebo-Controlled United States Cetirizine Trials (Maximum Dose of 10 mg) at Rates of 2% or Greater (Percent Incidence) Adverse Experience Cetirizine (N=2034) Placebo (N=1612) Somnolence 13.7 6.3 Fatigue 5.9 2.6 Dry Mouth 5.0 2.3 Pharyngitis 2.0 1.9 Dizziness 2.0 1.2 In addition, headache and nausea occurred in more than 2% of the patients, but were more common in placebo patients. Pediatric studies were also conducted with cetirizine. More than 1300 pediatric patients aged 6 to 11 years with more than 900 treated with cetirizine at doses of 1.25 to 10 mg per day were included in controlled and uncontrolled clinical trials conducted in the United States. The duration of treatment ranged from 2 to 12 weeks. Placebo-controlled trials up to 4 weeks duration included 168 pediatric patients aged 2 to 5 years who received cetirizine, the majority of whom received single daily doses of 5 mg. The majority of adverse reactions reported in pediatric patients aged 2 to 11 years with cetirizine were mild or moderate. In placebo-controlled trials, the incidence of discontinuations due to adverse reactions in pediatric patients receiving up to 10 mg of cetirizine was uncommon (0.4% on cetirizine vs. 1.0% on placebo). TABLE 2 lists adverse experiences which were reported for cetirizine 5 and 10 mg in pediatric patients aged 6 to 11 years in placebo-controlled clinical trials in the United States and were more common with cetirizine than placebo. Of these, abdominal pain was considered treatment-related and somnolence appeared to be dose-related, 1.3% in placebo, 1.9% at 5 mg and 4.2% at 10 mg. The adverse experiences reported in pediatric patients aged 2 to 5 years in placebo-controlled trials were qualitatively similar in nature and generally similar in frequency to those reported in trials with children aged 6 to 11 years. TABLE 2 Adverse Experiences Reported in Pediatric Patients Aged 6 to 11 Years in Placebo-Controlled United States Cetirizine Trials (5 or 10 mg Dose) Which Occurred at a Frequency of 2% in Either the 5-mg or the 10-mg Cetirizine Group, and More Frequently Than in the Placebo Group Cetirizine Adverse Experiences Placebo (N=309) 5 mg (N=161) 10 mg (N=215) Headache 12.3% 11.0% 14.0% Pharyngitis 2.9% 6.2% 2.8% Abdominal Pain 1.9% 4.4% 5.6% Coughing 3.9% 4.4% 2.8% Somnolence 1.3% 1.9% 4.2% Diarrhea 1.3% 3.1% 1.9% Epistaxis 2.9% 3.7% 1.9% Bronchospasm 1.9% 3.1% 1.9% Nausea 1.9% 1.9% 2.8% Vomiting 1.0% 2.5% 2.3% The following events were observed infrequently (less than 2%), in either 3982 adults and children 12 years and older or in 659 pediatric patients aged 6 to 11 years who received cetirizine in U.S. trials, including an open adult study of six months duration. A causal relationship of these infrequent events with cetirizine administration has not been established. Autonomic Nervous System : Anorexia, flushing, increased salivation, urinary retention. Cardiovascular : Cardiac failure, hypertension, palpitation, tachycardia. Central and Peripheral Nervous Systems : Abnormal coordination, ataxia, confusion, dysphonia, hyperesthesia, hyperkinesia, hypertonia, hypoesthesia, leg cramps, migraine, myelitis, paralysis, paresthesia, ptosis, syncope, tremor, twitching, vertigo, visual field defect. Gastrointestina l: Abnormal hepatic function, aggravated tooth caries, constipation, dyspepsia, eructation, flatulence, gastritis, hemorrhoids, increased appetite, melena, rectal hemorrhage, stomatitis including ulcerative stomatitis, tongue discoloration, tongue edema. Genitourinary : Cystitis, dysuria, hematuria, micturition frequency, polyuria, urinary incontinence, urinary tract infection. Hearing and Vestibular : Deafness, earache, ototoxicity, tinnitus. Metabolic/Nutritional: Dehydration, diabetes mellitus, thirst. Musculoskeletal : Arthralgia, arthritis, arthrosis, muscle weakness, myalgia. Psychiatric : Abnormal thinking, agitation, amnesia, anxiety, decreased libido, depersonalization, depression, emotional lability, euphoria, impaired concentration, insomnia, nervousness, paroniria, sleep disorder. Respiratory System : Bronchitis, dyspnea, hyperventilation, increased sputum, pneumonia, respiratory disorder, rhinitis, sinusitis, upper respiratory tract infection. Reproductive : Dysmenorrhea, female breast pain, intermenstrual bleeding, leukorrhea, menorrhagia, vaginitis. Reticuloendothelial : Lymphadenopathy. Skin : Acne, alopecia, angioedema, bullous eruption, dermatitis, dry skin, eczema, erythematous rash, furunculosis, hyperkeratosis, hypertrichosis, increased sweating, maculopapular rash, photosensitivity reaction, photosensitivity toxic reaction, pruritus, purpura, rash, seborrhea, skin disorder, skin nodule, urticaria. Special Senses : Parosmia, taste loss, taste perversion. Vision : Blindness, conjunctivitis, eye pain, glaucoma, loss of accommodation, ocular hemorrhage, xerophthalmia. Body as a Whole : Accidental injury, asthenia, back pain, chest pain, enlarged abdomen, face edema, fever, generalized edema, hot flashes, increased weight, leg edema, malaise, nasal polyp, pain, pallor, periorbital edema, peripheral edema, rigors. Occasional instances of transient, reversible hepatic transaminase elevations have occurred during cetirizine therapy. Hepatitis with significant transaminase elevation and elevated bilirubin in association with the use of cetirizine HCl has been reported. In foreign marketing experience the following additional rare, but potentially severe adverse events have been reported: anaphylaxis, cholestasis, glomerulonephritis, hemolytic anemia, hepatitis, orofacial dyskinesia, severe hypotension, stillbirth, and thrombocytopenia. DRUG ABUSE AND DEPENDENCE : There is no information to indicate that abuse or dependency occurs with cetirizine. OVERDOSAGE : Overdosage has been reported with cetirizine. In one adult patient who took 150 mg of cetirizine, the patient was somnolent but did not display any other clinical signs or abnormal blood chemistry or hematology results. In an 18-month-old pediatric patient who took an overdose of cetirizine (approximately 180 mg), restlessness and irritability were observed initially; this was followed by drowsiness. Should overdose occur, treatment should be symptomatic or supportive, taking into account any concomitantly ingested medications. There is no known specific antidote to cetirizine. Cetirizine is not effectively removed by dialysis, and dialysis will be ineffective unless a dialyzable agent has been concomitantly ingested. The acute minimal lethal oral doses were 237 mg/kg in mice (approximately 95 times the maximum recommended daily oral dose in adults on a mg/m2 basis, or approximately 55 times the maximum recommended daily oral dose in children on a mg/m2 basis) and 562 mg/kg in rats (approximately 460 times the maximum recommended daily oral dose in adults on a mg/m2 basis, or approximately 270 times the maximum recommended daily oral dose in children on a mg/m2 basis). In rodents, the target of acute toxicity was the central nervous system, and the target of multiple-dose toxicity was the liver. DOSAGE AND ADMINISTRATION : Adults and Children 12 Years and Older : The recommended initial dose of cetirizine is 5 or 10 mg per day in adults and children 12 years and older, depending on symptom severity. Most patients in clinical trials started at 10 mg. Cetirizine is given as a single daily dose, with or without food. The time of administration may be varied to suit individual patient needs. Children 6 to 11 Years : The recommended initial dose of cetirizine in children aged 6 to 11 years is 5 or 10 mg (1 or 2 teaspoons) once daily depending on symptom severity. The time of administration may be varied to suit individual patient needs. Children 2 to 5 Years : The recommended initial dose of cetirizine syrup in children aged 2 to 5 years is 2.5 mg (½ teaspoon) once daily. The dosage in this age group can be increased to a maximum dose of 5 mg per day given as 1 teaspoon (5 mg) once daily, or as ½ teaspoon (2.5 mg) given every 12 hours, depending on symptom severity and patient response. Dose Adjustment for Renal and Hepatic Impairment : In patients 12 years of age and older with decreased renal function (creatinine clearance 11-31 ml/min), patients on hemodialysis (creatinine clearance less than 7 ml/min), and in hepatically impaired patients, a dose of 5 mg once daily is recommended. Similarly, pediatric patients aged 6 to 11 years with impaired renal or hepatic function should use the lower recommended dose. Because of the difficulty in reliably administering doses of less than 2.5 mg (½ teaspoon) of cetirizine syrup and in the absence of pharmacokinetic and safety information for cetirizine in children below the age of 6 years with impaired renal or hepatic function, its use in this impaired patient population is not recommended. HOW SUPPLIED : Zyrtec Tablets White, film-coated, rounded-off rectangular shaped containing 5 mg or 10 mg cetirizine HCl. 5 mg tablets are engraved with “ZYRTEC” on one side and “5” on the other. 10 mg tablets are engraved with “ZYRTEC” on one side and “10” on the other. Storage : Store at room temperature 15-30°C (59-86°F). Zyrtec Syrup Colorless to slightly yellow with a banana-grape flavor. Each teaspoonful (5 ml) contains 5 mg cetirizine HCl. Storage : Store at 5-30°C (41-86°F).