4-[(4-chlorophenyl)methyl]-2- (1-methylazepan-4-yl)-phthalazin-1-one

Azelastine 是一個新的phthalazinone類衍生物，被歸類為長效性抗過敏化合物，並具特強的選擇性H1接收體阻斷之特性。根據體內和體外的研究顯示，Azelastine可以抑制過敏反應出奇及后齊之化學介質的合成及釋出，如leukotriene、histamine、PAF inhibitors和 serotonin。

Absorption：Bioavailability of nasal spray is approximately 40% and C max is 2 to 3 h. Absorption following ocular administration is relatively low, reaching a level of 0.02 to 0.25 ng/mL after 56 days of treatment.

Distribution：Vd is 14.5 L/kg. Approximately 88% (azelastine) and 97% (desmethylazelastine) are protein bound.

Metabolism：Oxidatively metabolized to desmethylazelastine (active) by CYP-450 system.

Elimination：The t ½ is 22 h for azelastine and 54 h for desmethylazelastine. Plasma Cl is 0.5 L/h/kg. Approximately 75% was excreted in the feces, with less than 10% as unchanged azelastine.

Special Populations
Renal Function Impairment
Based on oral doses, AUC and C max increased 70% to 75% in those with Ccr less than 50 mL/min.

Alcohol, other CNS depressants
Effects may be enhanced by azelastine.

Cimetidine
May increase azelastine plasma levels, increasing the risk of side effects.