(±) - [2- [4- [ (4-chlorophenyl)phenylmethyl] -1- piperazinyl] ethoxy]acetic acid, dihydrochloride
1. 迅速抑制外生性組織胺。
2. 對內生性組織胺的釋出有抑制作用(如48/80之組織胺)。
3. 抑制由VIP(Vasoactive Intenstinal Polypetide)和Substance P所引起之過敏反應。
4. 顯著的降低氣喘患者的支氣管對組織胺的過度反應。
5. 降低由特殊過敏原引起的過敏反應。這些作用，由心智測驗及Quantified EEG得知，對中樞神經不會產生任何作用。
3-6歲孩童：一天一次，每次 5 毫克(即5ml)，於晚餐時服用。或分別於早、晚各服用2.5毫克(即2.5ml)。
6歲以上：每次10毫克(即10ml)，一天一次，於晚餐時與液體伴服。
腎功能不全的患者服用本藥時，其劑量應減半。
Absorption
Rapidly absorbed. T max is about 1 h. C max is 311 ng/mL.
Food
T max is delayed 1.7 h, and C max is decreased 23%.
Distribution
93% protein bound.
Metabolism
Cetirizine has a low degree of first-pass metabolism. It also is metabolized by oxidative O-dealkylation to an inactive metabolite.
Elimination
70% is excreted in the urine (50% as unchanged drug) and 10% in the feces. The elimination half-life is 8.3 h. Cl is about 53 mL/min.
Onset
20 to 60 min.
Duration
At least 24 h.
Special Populations
Renal Function Impairment
Moderate impairment (CrCl 11 to 31 mL/min)
The half-life is increased 3-fold, and Cl is decreased 70%. Dosage adjustment is recommended in those with moderate or severe impairment.
Hepatic Function Impairment
The half-life is increased 50%, and Cl is decreased 40%. Dosage adjustment is recommended.
Elderly
The half-life is prolonged 50%, and Cl is 40% lower. Dosage adjustment is recommended.
Children
Cl is increased, and half-life is decreased.
2. 動物實驗上，尚無引起畸型胎之報告，但懷孕及哺乳的婦人請謹慎使用。
3. 至今尚未有藥物交互作用方面的報告，但若同時服用安眠藥者，請謹慎使用
4. 實驗證明，對正常人投予20～25mg/天的劑量，不會影響正常的睡眠及活動時間。但從事駕及操作機械者，請小心使用，儘量不要過量服用。
現今尚無特別的解毒劑，在大量過量的情況下，應儘快進行胃腸灌洗。除將一般急救支援性治療外，還必須定時監察所有的生命參數。
