Zyrtec-D

Patient Information

ZYRTEC-D® (cetirizine, pseudoephedrine) Tablets temporarily relieves these symptoms due to hay fever or other upper respiratory allergies:

• runny nose
• sneezing
• itchy, watery eyes
• itching of the nose or throat
• nasal congestion

Do not use

• if you have ever had an allergic reaction to this product or any of its ingredients or to an antihistamine containing hydroxyzine.
• if you are now taking a prescription monoamine oxidase inhibitor (MAOI) (certain drugs for depression, psychiatric, or emotional conditions, or Parkinson’s disease), or for 2 weeks after stopping the MAOI drug. If you do not know if your prescription drug contains an MAOI, ask a doctor or pharmacist before taking this product.

Ask a doctor before use if you have

• heart disease
• thyroid disease
• diabetes
• glaucoma
• high blood pressure
• trouble urinating due to an enlarged prostate gland
• liver or kidney disease. Your doctor should determine if you need a different dose.

Ask a doctor or pharmacist before use if you are taking tranquilizers or sedatives.

When using this product

• do not use more than directed
• drowsiness may occur
• avoid alcoholic drinks
• alcohol, sedatives, and tranquilizers may increase drowsiness
• be careful when driving a motor vehicle or operating machinery

Stop use and ask a doctor if

• an allergic reaction to this product occurs. Seek medical help right away.
• you get nervous, dizzy, or sleepless.
• symptoms do not improve within 7 days or are accompanied by fever.

If pregnant or breast-feeding

• If breast-feeding not recommended.
• If pregnant: ask a health professional before use.

Keep out of reach of children. In case of overdose, get medical help or contact a Poison Control Center right away.

Description

ZYRTEC-D® (cetirizine, pseudoephedrine) Tablets (cetirizine hydrochloride 5 mg and pseudoephedrine hydrochloride 120 mg) Extended Release Tablets for oral administration contain 5 mg of cetirizine hydrochloride for immediate release and 120 mg of pseudoephedrine hydrochloride for extended release in a bilayer tablet. Tablets also contain as inactive ingredients: colloidal silicon dioxide, croscarmellose sodium, hypromellose, lactose monohydrate, magnesium stearate, microcrystalline cellulose.

Cetirizine hydrochloride, one of the two active components of ZYRTEC-D (cetirizine, pseudoephedrine) Tablets, 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 hydrochloride is a racemic compound with an empirical formula of C₂₁H₂₅ClN₂O₃•2HCl. The molecular weight is 461.82. Cetirizine hydrochloride is a white, crystalline powder and is water-soluble.

Pseudoephedrine hydrochloride, the other active ingredient of ZYRTEC-D (cetirizine, pseudoephedrine) Tablets, is an adrenergic (vasoconstrictor) agent with the chemical name (1S.2S)-2-methylamino-1-phenyl-1-propanol hydrochloride. The molecular weight is 201.70. The molecular formula is C₁₀H₁₅NO•HCl. Pseudoephedrine hydrochloride occurs as fine, white to off-white crystals or powder, having a faint characteristic odor. It is very soluble in water, freely soluble in alcohol, and sparingly soluble in chloroform.

Active Ingredients

Inactive ingredients
colloidal silicon dioxide, croscarmellose sodium, hypromellose, lactose monohydrate, magnesium stearate, microcrystalline cellulose, polyethylene glycol, titanium dioxide

ZYRTEC-D® (cetirizine, pseudoephedrine) Tablets should be administered when both the antihistaminic properties of cetirizine hydrochloride and the nasal decongestant properties of pseudoephedrine hydrochloride are desired.

ZYRTEC-D (cetirizine, pseudoephedrine) Tablets are indicated for the relief of nasal and non-nasal symptoms associated with seasonal or perennial allergic rhinitis in adults and children 12 years of age and older.

Dosage And Administration

Do not break or chew tablet; swallow tablet whole

Adults and Children 12 Years and over:
take 1 tablet every 12 hours; do not take more than 2 tablets in 24 hours

Adults 65 years and over:
Ask a doctor

Children under 12 years of age:
Ask a doctor

Consumers with liver or kidney disease:
Ask a doctor

ZYRTEC-D (cetirizine, pseudoephedrine) Tablets may be given with or without food.

How Supplied

ZYRTEC-D (cetirizine, pseudoephedrine) Tablets are white, round, biconvex, bilayer tablets containing 5 mg cetirizine hydrochloride in an immediate release layer and 120 mg pseudoephedrine hydrochloride in an extended release layer. ZYRTEC-D (cetirizine, pseudoephedrine) Tablets are supplied in high-density polyethylene bottles of 100 tablets fitted with polypropylene child-resistant closures (NDC 0069-1630-66).

ZYRTEC-D (cetirizine, pseudoephedrine) Tablets are engraved with ZYRTEC-D (cetirizine, pseudoephedrine) on one side.

STORAGE: Store at 20°C to 25°C (68° to 77°F)

For questions contact McNEIL-PPC, Inc at 1.800.343.7805

ZYRTEC-D (cetirizine, pseudoephedrine) Tablets

In two double-blind, placebo-controlled trials (n = 2094) in which 701 patients with seasonal allergic rhinitis were treated with ZYRTEC-D (cetirizine, pseudoephedrine) Tablets (cetirizine hydrochloride 5 mg and pseudoephedrine hydrochloride 120 mg) twice daily for two weeks, the percent of patients who withdrew prematurely due to adverse events was 2.0% in the ZYRTEC-D (cetirizine, pseudoephedrine) group, compared with 1.1% in the placebo group. All adverse events that were reported by greater than 1% of patients in the ZYRTEC-D (cetirizine, pseudoephedrine) group are listed in Table 1.

TABLE 1. ADVERSE EXPERIENCES REPORTED IN PATIENTS AGED 12 YEARS AND OLDER IN SEASONAL ALLERGIC RHINITIS TRIALS OF ZYRTEC-D (cetirizine, pseudoephedrine) TABLETS AT RATES OF 1% OR GREATER (PERCENT INCIDENCE)

ZYRTEC Tablets

Controlled and uncontrolled clinical trials of cetirizine 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 mg 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 2 lists adverse experiences in patients aged 12 years and older that were reported for cetirizine 5 and 10 mg in controlled clinical trials in the United States and were more common with cetirizine than placebo.

TABLE 2. 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)

In addition, headache and nausea occurred in more than 2% of the patients, but were more common in placebo patients.

The following events were observed infrequently (less than 2%), in 3982 adults and children 12 years and older or in 659 pediatric (6 to 11 years) patients who received cetirizine in U.S. trials, including an open 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.

Gastrointestinal: 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 has been reported.

In foreign marketing experience or experience in the post market period, the following additional rare, but potentially severe adverse events have been reported: anaphylaxis, cholestasis, glomerulonephritis, hemolytic anemia, hepatitis, orofacial dyskinesia, severe hypotension, stillbirth, thrombocytopenia, aggressive reaction and convulsions.

Pseudoephedrine Hydrochloride

Pseudoephedrine hydrochloride may cause mild CNS stimulation in hypersensitive patients.

Nervousness, excitability, restlessness, dizziness, weakness, or insomnia may occur. Headache, nausea, drowsiness, tachycardia, palpitation, pressor activity, and cardiac arrhythmias have been reported. Sympathomimetic drugs have also been associated with other untoward effects such as fear, anxiety, tenseness, tremor, hallucinations, seizures, pallor, respiratory difficulty, dysuria, and cardiovascular collapse.

Cetirizine hydrochloride and pseudoephedrine hydrochloride do not influence the pharmacokinetics of each other when administered concomitantly.

No clinically significant drug interactions have been found with cetirizine and theophylline at a low dose, azithromycin, 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.

Due to the pseudoephedrine component, ZYRTEC-D (cetirizine, pseudoephedrine) Tablets are contraindicated in patients taking monoamine oxidase (MAO) inhibitors and for 14 days after stopping use of an MAO inhibitor. Concomitant use with antihypertensive drugs that interfere with sympathetic activity (e.g., methyldopa, mecamylamine, and reserpine) may reduce their antihypertensive effects. Increased ectopic pacemaker activity can occur when pseudoephedrine is used concomitantly with digitalis. Care should be taken in the administration of ZYRTEC-D (cetirizine, pseudoephedrine) Tablets concomitantly with other sympathomimetic amines because combined effects on the cardiovascular system may be harmful to the patient (see WARNINGS).

Sympathomimetic amines should be used judiciously and sparingly in patients with hypertension, diabetes mellitus, ischemic heart disease, increased intraocular pressure, hyperthyroidism, renal impairment, or prostatic hypertrophy (see CONTRAINDICATIONS). Sympathomimetic amines may produce central nervous system stimulation with convulsions or cardiovascular collapse with accompanying hypotension. The elderly are more likely to have adverse reactions to sympathomimetic amines.

Due to its pseudoephedrine component, ZYRTEC-D (cetirizine, pseudoephedrine) Tablets should be used with caution in patients with hypertension, diabetes mellitus, ischemic heart disease, increased intraocular pressure, hyperthyroidism, renal impairment, or prostatic hypertrophy (see WARNINGS and CONTRAINDICATIONS). Patients with decreased renal function should be given a lower initial dose (one tablet per day) because they have reduced elimination of cetirizine and pseudoephedrine (see CLINICAL PHARMACOLOGY and DOSAGE AND ADMINISTRATION).

Activities Requiring Mental Alertness

In clinical trials, the occurrence of somnolence has been reported in some patients taking cetirizine or ZYRTEC-D (cetirizine, pseudoephedrine) Tablets; due caution should therefore be exercised when driving a car or operating potentially dangerous machinery after taking ZYRTEC-D (cetirizine, pseudoephedrine) Tablets. Concurrent use of ZYRTEC-D (cetirizine, pseudoephedrine) Tablets 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

There are no carcinogenicity trials of pseudoephedrine and cetirizine in combination.

Cetirizine: In a 2-year study in rats, cetirizine was not carcinogenic at dietary doses up to 20 mg/kg (approximately 15 times the maximum recommended daily dose in adults on a mg/m² basis). In a 2-year 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 dose in adults 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 dose in adults on a mg/m² basis). The clinical significance of these findings during long-term use of ZYRTEC-D (cetirizine, pseudoephedrine) Tablets is not known.

Pseudoephedrine: Two-year studies in rats and mice conducted under the auspices of the National Toxicology Program (NTP) demonstrated no evidence of carcinogenic potential with ephedrine sulfate, a structurally related drug with pharmacological properties similar to pseudoephedrine, at dietary doses up to 10 and 27 mg/kg, respectively (approximately 1/3 and 1/2, respectively, the maximum recommended daily dose of pseudoephedrine in adults on a mg/m² basis).

Cetirizine was not mutagenic in the Ames test or mouse lymphoma test and not clastogenic in the human lymphocyte assay or the in vivo rodent micronucleus test. Likewise, the combination of cetirizine and pseudoephedrine in a 1:24 ratio was not mutagenic or clastogenic in these tests. However, the Ames and mouse lymphoma assays did not strictly adhere to test standards.

In a reproductive toxicity study in rats, combination oral doses of cetirizine and pseudoephedrine up to 6/154 mg/kg (approximately 5 times the maximum recommended daily dose in adults on a mg/m² basis) had no effect on fertility.

Pregnancy Category C

In rats, the combination of cetirizine and pseudoephedrine caused developmental toxicity when administered orally at 6/154 mg/kg (approximately 5 times the maximum recommended daily dose in adults on a mg/m² basis). When rats were dosed throughout pregnancy with oral doses of cetirizine/pseudoephedrine, 6/154 mg/kg increased the number of fetal skeletal malformations (rib distortions) and variants (unossified sternebrae). When dosing was continued through lactation, 6/154 mg/kg also decreased the viability and weight gain of offspring. These effects were not observed at 1.6/38 mg/kg (approximately equivalent to the maximum recommended daily dose in adults on a mg/m² basis). No embryofetal toxicity was observed when rabbits were dosed throughout organogenesis with oral doses of cetirizine/pseudoephedrine of up to 6/154 mg/kg (approximately 10 times the maximum recommended daily dose in adults on a mg/m² basis). Because there are no adequate and well-controlled trials in pregnant women, ZYRTEC-D (cetirizine, pseudoephedrine) Tablets should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Nursing Mothers

In rats the combination of cetirizine/pseudoephedrine decreased the viability and weight gain of offspring when administered orally to dams throughout pregnancy and lactation at 6/154 mg/kg (approximately 5 times the maximum recommended daily dose in adults on a mg/m² basis). This effect was not observed at 1.6/38 mg/kg (approximately equivalent to the maximum recommended daily dose in adults on a mg/m² basis). For cetirizine administered alone, studies in dogs indicate that approximately 3% of the dose is excreted in milk, and cetirizine has been reported to be excreted in human breast milk. For pseudoephedrine administered alone, 0.4-0.7% of the dose has been reported to be excreted in human breast milk.

Because cetirizine and pseudoephedrine are excreted in milk, use of ZYRTEC-D (cetirizine, pseudoephedrine) Tablets in nursing mothers is not recommended.

Geriatric Use

Clinical trials of ZYRTEC-D (cetirizine, pseudoephedrine) Tablets did not include sufficient numbers of patients aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients, although the elderly are more likely to have adverse reactions to sympathomimetic amines. In general, dosing in an elderly patient should be cautious, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

The cetirizine and pseudoephedrine components of ZYRTEC-D (cetirizine, pseudoephedrine) Tablets are known to be substantially excreted by the kidney, and the risk of toxic reactions to this drug may be greater in patients with impaired renal function. Because elderly patients are more likely to have decreased renal function, care should be taken in dose selection, and it may be useful to monitor renal function (see CLINICAL PHARMACOLOGY).

Cetirizine: Of the total number of subjects in clinical trials of cetirizine alone, 186 were 65 years and over, while 39 were 75 years and over. No overall differences in safety were observed between these subjects and younger subjects, and other reported experience has not identified differences in responses between the elderly and younger patients, but greater sensitivity of some older individuals cannot be ruled out. With regard to efficacy, clinical trials of cetirizine for each approved indication did not include sufficient numbers of subjects aged 65 years and over to determine whether they respond differently than younger patients.

Pediatric Use

ZYRTEC-D (cetirizine, pseudoephedrine) Tablets contain 120 mg of pseudoephedrine hydrochloride in an extended release formulation. This dose of pseudoephedrine exceeds the recommended dose for pediatric patients under 12 years of age. Therefore, clinical trials of ZYRTEC-D (cetirizine, pseudoephedrine) Tablets have not been conducted in patients under 12 years of age.

Information regarding acute overdosage is limited to experience with cetirizine alone and the marketing history of pseudoephedrine hydrochloride.

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 in mice and rats were 237 and 562 mg/kg, respectively (approximately 95 and 460 times the maximum recommended daily dose in adults 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.

In large doses, sympathomimetics may give rise to giddiness, headache, nausea, vomiting, sweating, thirst, tachycardia, precordial pain, palpitations, difficulty in micturition, muscular weakness and tenseness, anxiety, restlessness, and insomnia. Many patients can present a toxic psychosis with delusions and hallucinations. Some may develop cardiac arrhythmias, circulatory collapse, convulsions, coma and respiratory failure.

ZYRTEC-D (cetirizine, pseudoephedrine) Tablets are contraindicated in patients with a known hypersensitivity to any of its ingredients or to hydroxyzine.

Due to its pseudoephedrine component, ZYRTEC-D (cetirizine, pseudoephedrine) Tablets are contraindicated in patients with narrow-angle glaucoma or urinary retention, and in patients receiving monoamine oxidase (MAO) inhibitor therapy or within fourteen (14) days of stopping such treatment (see PRECAUTIONS, Drug Interactions section). It is also contraindicated in patients with severe hypertension, or severe coronary artery disease, and in those who have shown hypersensitivity or idiosyncrasy to its components, to adrenergic agents, or to other drugs of similar chemical structures. Manifestations of patient idiosyncrasy to adrenergic agents include insomnia, dizziness, weakness, tremor, or arrhythmias.

Mechanisms of Action

Cetirizine, a metabolite of hydroxyzine, is an antihistamine; its principal effects are mediated via selective inhibition of 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 trials, 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.

Pseudoephedrine hydrochloride is an orally active sympathomimetic amine and exerts a decongestant action on the nasal mucosa. Pseudoephedrine hydrochloride is recognized as an effective agent for the relief of nasal congestion due to allergic rhinitis. Pseudoephedrine produces peripheral effects similar to those of ephedrine and central effects similar to, but less intense than, amphetamines. It has the potential for excitatory side effects.

Pharmacokinetics

Absorption

The bioavailability of cetirizine hydrochloride and pseudoephedrine hydrochloride from ZYRTEC-D (cetirizine, pseudoephedrine) Tablets is not significantly different from that achieved with separate administration of a cetirizine 5 mg tablet and a pseudoephedrine 120 mg extended release caplet. Co-administration of cetirizine and pseudoephedrine does not significantly affect the bioavailability of either component.

Following a single dose of the ZYRTEC-D (cetirizine, pseudoephedrine) Tablet, a mean peak plasma concentration (Cmax) of 114 ng/mL at a time (Tmax) of 2.2 hours postdose was observed for cetirizine and a mean Cmax of 309 ng/mL at a Tmax of 4.4 hours postdose was observed for pseudoephedrine.

When healthy volunteers were administered multiple doses of the ZYRTEC-D (cetirizine, pseudoephedrine) Tablet to reach steady-state concentrations (cetirizine hydrochloride 5 mg and pseudoephedrine hydrochloride 120 mg twice daily for seven days), a mean Cmax of 178 ng/mL was observed for cetirizine and 526 ng/mL for pseudoephedrine.

Food had no significant effect on the extent of cetirizine absorption (AUC), but Tmax was delayed by 1.8 hours and Cmax was decreased by 30%. Food had no significant effect on the pharmacokinetics of pseudoephedrine. ZYRTEC-D (cetirizine, pseudoephedrine) Tablets may be given with or without food (see DOSAGE AND ADMINISTRATION).

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. The apparent volume of distribution (V/F) of pseudoephedrine has been reported to be 2.6-3.3 L/kg. No plasma protein binding data in humans are available.

Metabolism

A human mass balance study of cetirizine 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 low 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.

One to seven percent of the pseudoephedrine dose appeared to be metabolized to norpseudoephedrine by N-demethylation after a single dose.

Elimination

After administration of the ZYRTEC-D (cetirizine, pseudoephedrine) Tablet, the mean elimination half-life of cetirizine was 7.9 hours and the mean elimination half-life of pseudoephedrine was 6.0 hours.

It was reported that 0.4-0.7% of the pseudoephedrine dose was estimated to be excreted in the breast milk over 24 hours after a single dose. The pattern of the relative milk/plasma drug concentration profile showed that pseudoephedrine concentrations in milk were 2- to 3-fold higher than those in plasma.

DRUG INTERACTIONS

Pharmacokinetic interaction trials 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.

Special Populations

Pediatrics: Although cetirizine pharmacokinetics have been studied in children, ZYRTEC-D (cetirizine, pseudoephedrine) Tablets contain 120 mg of pseudoephedrine hydrochloride, which exceeds the recommended dose for patients less than 12 years of age. Therefore, ZYRTEC-D (cetirizine, pseudoephedrine) Tablets are not recommended for patients under 12 years of age.

Geriatrics: Following a single, 10-mg oral dose of cetirizine, 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.

The pharmacokinetics of pseudoephedrine has not been adequately studied in geriatric subjects.

Gender: The effect of gender on cetirizine or pseudoephedrine pharmacokinetics has not been adequately studied.

Race: The effect of race on cetirizine or pseudoephedrine pharmacokinetics has not been adequately studied.

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.

About 55-75% of an administered dose of pseudoephedrine hydrochloride is excreted unchanged in the urine; the remainder is apparently metabolized in the liver. Therefore, pseudoephedrine may accumulate in patients with renal insufficiency.

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.

The effect of hepatic impairment on pseudoephedrine pharmacokinetics is unknown.

Dosing adjustment may be necessary in patients with hepatic impairment (see DOSAGE AND ADMINISTRATION).

Pharmacodynamics: Trials in 69 adult normal volunteers (aged 20-61 years) showed that cetirizine at doses of 5 and 10 mg 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. The effects of intradermal injection of various other mediators or histamine releasers were also inhibited by cetirizine. 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 trials 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. The clinical significance of these findings is not known.

In four clinical trials 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 six-week, placebo-controlled study of 186 patients (aged 12-64 years) with allergic rhinitis and mild to moderate asthma, cetirizine 10 mg once daily improved rhinitis symptoms and did not alter pulmonary function. This study supports the safety of administering cetirizine to allergic rhinitis patients with mild to moderate asthma.

Clinical Trials

ZYRTEC-D (cetirizine, pseudoephedrine) Tablets: Two multicenter, randomized, double-blind, placebo-controlled clinical trials (n = 1094 and n = 1000) comparing ZYRTEC-D (cetirizine, pseudoephedrine) Tablets (cetirizine hydrochloride 5 mg and pseudoephedrine hydrochloride 120 mg) to active control and placebo for two weeks in patients 12 years and older with seasonal allergic rhinitis were conducted in the United States. In the two trials, 390 patients were aged 12 to 17 years. The primary efficacy measure in both trials was the mean change from baseline in the subject-rated Total Symptom Severity Complex (TSSC) score, which included the following symptoms: sneezing, runny nose, itchy nose, itchy eyes, watery eyes, postnasal drip, and nasal congestion. In both trials patients who received ZYRTEC-D (cetirizine, pseudoephedrine) showed a significant reduction in the TSSC score compared to those who received placebo.

Zyrtec Tablets: 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. 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.