Wang D Y, Hanotte F, De Vos C, Clement P
National University of Singapore, Singapore.
Allergy. 2001 Apr;56(4):339-43. doi: 10.1034/j.1398-9995.2001.00775.x.
Cetirizine, an effective H1-receptor antagonist, is a racemate mixture of two enantiomers: levocetirizine (R enantiomer) and dextrocetirizine (S enantiomer).
To investigate the pharmacologic activity of the two enantiomers of cetirizine, we conducted a randomized, double-blind, four-way, crossover study to assess the effect of treatment with 5 mg levocetirizine, 5 mg dextrocetirizine, and 10 mg cetirizine and matched placebo, on histamine-induced changes in the nasal airways of 24 healthy volunteers. Four hours after a single oral intake, all subjects were challenged by nasal aerosol application with increasing doubling concentrations (from 0.25 to 32 mg/ml) of histamine in both nostrils. Nasal resistance was measured by passive anterior rhinomanometry (PAR), and changes in histamine threshold were calculated together with the absolute number of sneezes after each challenge.
Both levocetirizine and cetirizine significantly attenuated the histamine-induced increase in nasal airway resistance by nearly 50% (from a median resistance of 2.51 Pa per cm3/s to 1.29 and 1.31 Pa per cm3/s, respectively) at the maximal concentration, and they concomitantly increased the histamine threshold by fourfold (from 8 to 32 mg/ml), compared with placebo. Sneezing was also attenuated by both levocetirizine and cetirizine. However, these antihistaminic effects were not seen with dextrocetirizine.
This study shows a similar activity of levocetirizine and cetirizine on the inhibition of histamine-induced increase in nasal resistance, indicating that the antihistaminic properties of cetirizine are probably attributable to levocetirizine.
西替利嗪是一种有效的H1受体拮抗剂，是两种对映体的外消旋混合物：左西替利嗪（R对映体）和右西替利嗪（S对映体）。
为研究西替利嗪两种对映体的药理活性，我们进行了一项随机、双盲、四组交叉研究，以评估5毫克左西替利嗪、5毫克右西替利嗪、10毫克西替利嗪及匹配安慰剂治疗对24名健康志愿者鼻气道中组胺诱导变化的影响。单次口服4小时后，所有受试者双侧鼻孔用浓度成倍增加（从0.25至32毫克/毫升）的组胺鼻喷雾剂进行激发。通过被动前鼻测压法（PAR）测量鼻阻力，并计算每次激发后组胺阈值的变化以及喷嚏的绝对次数。
在最大浓度时，左西替利嗪和西替利嗪均显著减轻组胺诱导的鼻气道阻力增加近50%（中位阻力分别从每立方厘米每秒2.51帕降至1.29和1.31帕），并且与安慰剂相比，它们使组胺阈值增加了四倍（从8毫克/毫升增至32毫克/毫升）。左西替利嗪和西替利嗪也都减轻了喷嚏症状。然而，右西替利嗪未观察到这些抗组胺作用。
本研究表明左西替利嗪和西替利嗪在抑制组胺诱导的鼻阻力增加方面具有相似活性，表明西替利嗪的抗组胺特性可能归因于左西替利嗪。
