Brand Name, Dosage Format and Strength
Alnix 5 mg/5 mL Syrup
H1-receptor antagonist, Corticosteroid, Antihistamine,Nasal Corticosteroid, H1-receptor antagonist, Alpha adrenergic agonist, Ethanolamine
Cetirizine is a potent H1-receptor antagonist. It is the carboxylic acid metabolite of hydroxyzine and is the principal human metabolite of hydroxyzine. The presence of the carboxylic group in cetirizine makes the molecule more polar and less likely to cross the blood-brain barrier. Cetirizine is therefore, less likely to cause sedation compared with the first generation antihistamines.
Cetirizine is rapidly and almost completely absorbed after oral administration. It reaches mean peak plasma concentration within 1 hr after administration of 10 mg and 20 mg doses. Food does not reduce the extent of cetirizine absorption, although it may slightly reduce the rate of absorption. The AUC increases proportionately with dose, with values 2.87 and 5.80 mg×hr/L following 10 mg and 20 mg doses respectively, in adults and 2.87 and 6.37 mg×hr/L following 5 mg and 10 mg doses in children. Cetirizine’s Vd at steady state is 33.2 L after oral administration of a single 20 mg dose and 40.8 L after a single administratin of 10 mg dose in healthy volunteers. There is no published information on the extent to which cetirizine is excreted in breast milk, nor on its placental transfer. The plasma concentration of cetirizine decreases bioexponentially; the terminal elimination half-life in healthy adults ranges from 6.7 hrs to 10.9 hrs. Cetirizine’s t½ is slightly shorter in children than in adults, with values of 6.9-7.1 hrs reported. The total body clearance of cetirizine, assuming complete absorption, is 0.04-0.05 L/hr/kg in adults and 0.06-0.07L/hr/kg in children. In young children, under 4 yrs old, the average half-life of cetirizine is 5.55 hrs. Elimination is slightly prolonged in the elderly compared with younger adults (t½: 11.8 hrs vs. 7.4 hrs) due to impaired renal function. The t½ is increased markedly in renal dysfunction, with values of 19 and 21 hrs in patients with mild and moderate renal impairment, respectively (CLCR: 1.9-3.6 L/hr and 0.42-1.8 L.hr). In patients with moderate renal impairment, the Tmax (2.2 hrs) is also significantly prolonged. The t½ is slightly prolonged in patients with hepatic dysfunction. Adjustment of dosage is necessary in patients with renal and hepatic impairment. Cetirizine is eliminated mainly by renal excretion of the unchanged drug, although there is a small amount of metabolism in the liver. Approximately 70% of the dose is excreted in the urine over 5 days, 60% over the first 24 hrs, with only 10% in the feces over 5 days.