Cetirizine HCl
(Zyrtec®)
Generic Name : Cetirizine hydrochloride
Dosage Form : syrup
Type of medicine : Antihistamine (non-drowsy)
Classification: Antihistamine
Pharmacology:
Cetirizine HCl is an active, human metabolite of hydroxyzine. It selectively binds peripheral histamine H1 receptors, competitively inhibiting the actions of histamine with no measureable affinity for histamine H2 receptors in in vitro studies. Unlike similar first generation H1-antagonists, cetirizine has a hydrophilic, carboxyl tail that effectively decreases CNS penetration resulting in minimal anticholinergic effects. While the mechanisms are unclear, cetirizine has also been shown to interfere with late phase inflammatory mediators.
Pharmacokinetics:
Absorption Following oral administration, cetirizine HCl is rapidly absorbed, reaching Tmax in approximately 1 hour. Food does not affect the AUC, but does delay Tmax by 1.7 hours and decreases Cmax by 23%.
Distribution Approximately 93% protein bound
Metabolism Cetirizine HCl undergoes limited first-pass metabolism. There is minimal metabolism via O-dealkylation resulting in a metabolite with negligible anti-histaminic activity.
Elimination Cetirizine HCl is excreted in the urine (70%) primarily unchanged and in the feces (10%). Mean elimination half-life is approximately 8.3 hours.
Indications:
Cetirizine is indicated for the treatment and management of symptoms of seasonal/perennial allergic rhinitis and chronic urticaria in adults and children as young as 6 months of age.
Dosage:
For adults and children over 6 years old, the initial recommended dose is 5 mg or 10 mg as a single dose depending on symptom severity. For children 2-5 years of age, the initial recommended dose is 2.5 mg daily, max 5 mg daily.
Contraindications:
• Hypersensitivity to cetirizine HCl or hydroxyzine
Precautions:
• Avoid activities requiring alertness until the effects are known
• Avoid concomitant use of CNS depressants
• Not recommended for lactating mothers, due to excretion in breast milk
• Renal/hepatic dysfunction requires dose adjustments
• Pregnancy Category B
Interactions:
Non-significant drug interactions have been reported with azithromycin, erythromycin, pseudoephedrine. Concomitant ketoconazole use has been associated with reports of transient ECG changes including QT prolongation of up to 17.4 msec, but these findings were considered to be non-clinically significant. Low-dose theophylline (400 mg) caused a non-clinically significant decrease in cetirizine HCl clearance.