Usage
Cetirizine is primarily prescribed for the symptomatic relief of allergic conditions such as:
- Seasonal allergic rhinitis (hay fever): Nasal congestion, runny nose, sneezing, itchy nose and throat, and watery eyes caused by pollen, mold, and other allergens.
- Perennial allergic rhinitis: Similar symptoms to hay fever, but occurring year-round due to allergens like dust mites, pet dander, and cockroaches.
- Chronic idiopathic urticaria (hives): Itchy, raised welts on the skin.
Pharmacological Classification: Cetirizine is a second-generation antihistamine.
Mechanism of Action: Cetirizine competitively inhibits the binding of histamine to H1 receptors. This action reduces the vascular permeability and formation of edema associated with allergic reactions. It also decreases the release of other mediators of inflammation.
Alternate Names
- Cetirizine hydrochloride (the salt form)
- Several generic formulations are available.
Brand Names:
- Zyrtec
- Aller-Tec
- Alleroff
- Quzyttir
- Reactine (Canada)
- Benadryl Allergy (some formulations)
How It Works
Pharmacodynamics: Cetirizine primarily acts by blocking the effects of histamine at H1 receptors, reducing the symptoms of allergic reactions. It is considered a non-sedating antihistamine as it poorly penetrates the blood-brain barrier.
Pharmacokinetics:
- Absorption: Well-absorbed orally, with peak plasma concentrations reached in approximately 1 hour. Food does not significantly affect absorption but might slightly delay peak concentrations.
- Metabolism: Minimally metabolized in the liver.
- Elimination: Primarily excreted unchanged in the urine, with a half-life of about 8-11 hours.
Mode of Action: Cetirizine competitively binds to peripheral H1 receptors, preventing histamine from binding and triggering the cascade of events that lead to allergic symptoms.
Receptor Binding: Selective for H1 receptors, with minimal affinity for other receptors.
Enzyme Inhibition/Neurotransmitter Modulation: No significant enzyme inhibition or neurotransmitter modulation effects.
Elimination Pathways: Predominantly renal excretion.
Dosage
Standard Dosage
Adults:
- 10 mg orally once daily. A 5 mg dose may be sufficient for milder symptoms. The maximum dose is 10 mg per 24 hours.
Children:
- 6-11 years: 5 mg twice daily, or 10mg once daily.
- 2-5 years: 2.5 mg once daily, which may be increased to a maximum of 5 mg per day (either as a single dose or divided into two 2.5 mg doses 12 hours apart).
- 6 months - 23 months: 2.5 mg once daily.
- Under 6 months: Use is not recommended unless under direct medical supervision.
Special Cases:
- Elderly Patients: A starting dose of 5 mg once daily is often recommended due to potential age-related decrease in renal function.
- Patients with Renal Impairment: Dose reduction is necessary based on the degree of impairment. For moderate renal impairment, 5 mg once daily is usually recommended.
- Patients with Hepatic Dysfunction: Dose adjustments are generally not required unless there is concomitant renal impairment.
- Patients with Comorbid Conditions: Dose adjustments might be necessary on a case-by-case basis.
Clinical Use Cases
Cetirizine is not typically administered in clinical settings like intubation, surgical procedures, mechanical ventilation, or ICU. It is not indicated for emergency situations. However, it can be administered intravenously to treat acute urticaria in children and adults.
- Intravenous administration
- Children 6 months to 5 years: 2.5mg every 24 hours as needed
- Children 6-11 years: 5-10 mg every 24 hours depending on severity
- 12 years and older: 10mg every 24 hours
Dosage Adjustments
Dose adjustments are required for patients with renal impairment. Consult specific guidelines for creatinine clearance-based dose recommendations.
Side Effects
Common Side Effects:
- Somnolence (drowsiness)
- Fatigue
- Dry mouth
- Headache
Rare but Serious Side Effects:
- Angioedema (severe swelling)
- Anaphylaxis (severe allergic reaction)
- Severe skin reactions (e.g., Stevens-Johnson syndrome)
Long-Term Effects:
No significant long-term effects have been reported.
Adverse Drug Reactions (ADR):
Any severe allergic reaction (anaphylaxis, angioedema) should be treated as a medical emergency.
Contraindications
- Hypersensitivity to cetirizine or hydroxyzine.
- Severe renal impairment (end-stage renal disease).
Drug Interactions
- CNS Depressants: Alcohol or other drugs with sedative properties can enhance the sedative effects of cetirizine.
- Theophylline: May decrease the clearance of cetirizine.
Pregnancy and Breastfeeding
- Pregnancy Safety Category: Category B. While generally considered safe, use only if clearly needed.
- Breastfeeding: Cetirizine is excreted in breast milk. Use with caution in breastfeeding mothers.
Drug Profile Summary
- Mechanism of Action: Competitive H1 receptor antagonist.
- Side Effects: Somnolence, fatigue, dry mouth, headache. Rarely, angioedema, anaphylaxis.
- Contraindications: Hypersensitivity, severe renal impairment.
- Drug Interactions: CNS depressants, theophylline.
- Pregnancy & Breastfeeding: Category B; use with caution if breastfeeding.
- Dosage: Adults: 10 mg/day; Children: refer to pediatric dosage charts.
- Monitoring Parameters: No specific routine monitoring required. Monitor for adverse effects.
Popular Combinations
Cetirizine is sometimes combined with pseudoephedrine (a decongestant) for the relief of combined nasal congestion and allergy symptoms.
Precautions
- General Precautions: Patients with renal or hepatic impairment may require dosage adjustments.
- Specific Populations: Elderly patients should start at a lower dose. Use with caution during pregnancy and breastfeeding.
- Lifestyle Considerations: Avoid alcohol and other CNS depressants that may exacerbate drowsiness. Caution with activities requiring alertness (e.g., driving).
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Cetirizine?
A: Adults and children 12 years and older: 10 mg once daily. Children 6-11 years: 5 mg twice daily or 10mg once daily. Children 2-5 years: 2.5 mg once daily (can increase to 5mg/day). Children 6 months - 23 months: 2.5 mg once daily. Adjust dosage for renal impairment.
Q2: Can cetirizine be used in pregnant women?
A: Cetirizine is Pregnancy Category B. It’s generally considered safe, but use only when clearly needed and after assessing the potential risks and benefits with the patient.
Q3: Does cetirizine cause drowsiness?
A: Although a second-generation antihistamine, cetirizine can cause some drowsiness in certain individuals. It is generally less sedating than first-generation antihistamines. Advise patients about potential drowsiness and recommend caution when driving or operating machinery.
Q4: How long does it take for cetirizine to work?
A: Cetirizine starts working relatively quickly, usually within 1-2 hours after administration.
Q5: What are the most common side effects of cetirizine?
A: The most common side effects are somnolence, fatigue, dry mouth, and headache.
Q6: Are there any drug interactions with cetirizine?
A: Yes. Cetirizine can interact with CNS depressants (e.g., alcohol, sedatives), enhancing drowsiness. It can also interact with theophylline.
Q7: Can cetirizine be used in patients with renal impairment?
A: Yes, but dose reduction is necessary. For moderate renal impairment, 5 mg once daily is usually recommended. Consult specific guidelines for severe renal impairment.
Q8: Can cetirizine be used in patients with liver disease?
A: Dose adjustments are usually not necessary unless there is concomitant renal impairment.
Q9: What should patients do if they miss a dose of cetirizine?
A: Take the missed dose as soon as they remember. However, if it is almost time for the next dose, skip the missed dose and continue with their regular dosing schedule. Do not double the dose.
Q10: What is the difference between cetirizine and levocetirizine?
A: Levocetirizine is the active enantiomer of cetirizine. It has a similar mechanism of action but is generally considered slightly more potent.
