セチリジン
**セチリジン (Cetirizine)** は**第2世代ヒスタミンH1受容体拮抗薬**であり、人間医療で広く使用されているほか、犬や猫のアレルギーおよびヒスタミン介在性のそう痒（かゆみ）の補助治療として獣医療でも利用が増えています。 * **非鎮静作用**：第1世代の抗ヒスタミン薬（ジフェンヒドラミンなど）とは異なり、セチリジンは標準用量で血液脳関門を通過しにくいため、眠気を引き起こしにくい特徴があります。 * **活性代謝物**：ピペラジン系誘導体であり、ヒドロキシジンの主要なヒト活性代謝物です。 * **臨床的有用性**：主に犬や猫のアトピー性皮膚炎、猫の慢性鼻副鼻腔炎の補助治療、および馬のアレルギー症状に使用されます。ペットの重度のアレルギー発作に対する単独療法としての効果は人間ほど高くありませんが、ステロイドの減量を目的とした多角的アプローチの一部として有用です。
作用機序: Cetirizine acts as a highly selective, competitive antagonist at peripheral **H1 receptors**. * **Allergic cascade**: Allergen exposure → Mast cell/basophil degranulation → **Histamine** release → Binds to **H1 receptors** on sensory nerve endings and blood vessels → Pruritus, vasodilation, and edema. * Cetirizine competitively blocks this binding, preventing histamine-mediated effects. * It also appears to decrease histamine release from basophils in some species, though experimental studies in cats showed it does not reduce eosinophilic airway inflammation. * It lacks significant anticholinergic or anti-serotonergic activity, and tolerance to its antihistaminic effects is not thought to occur.
動物種別の用量
- For adjunctive treatment of non-responsive chronic rhinosinusitis · 5 mg (total dose) PO q12h · PO · q12h
- General antihistamine use · 5 mg (total dose) per cat PO once daily · PO · q24h · No controlled studies evaluating effectiveness against other antihistamines.
- For adjunctive treatment of pruritus · 2.5-5 mg (total dose) per cat once daily · PO · q24h
- Antihistamine · 0.2-0.4 mg/kg PO q12h · PO · q12h · Based on pharmacokinetic and pharmacodynamic data, may be a useful antihistamine in horses.
- For atopic dermatitis · 1 mg/kg PO once daily with or without food · PO · q24h · Satisfactory control of pruritus in 18% of dogs evaluated in the study.
- For atopic dermatitis · 5-10 mg (total dose) PO once daily · PO · q24h
- For allergic dermatitis · 1 mg/kg PO q12h · PO · q12h
- For adjunctive treatment of pruritus · 0.5-1 mg/kg or 5-10 mg total dose once to twice daily · PO · q12-24h
用量は獣医療従事者向けの臨床リファレンスです。必ず最新の添付文書と個々の患者で確認してください。
投与経路
禁忌
- Hypersensitivity to cetirizine or hydroxyzine
- Combination products containing pseudoephedrine (e.g., Zyrtec-D) are strictly contraindicated in dogs and cats
有害事象
- Vomiting
- Hypersalivation (drooling)
- Somnolence (drowsiness/sedation, especially in small dogs at higher dosages)
- Dry mouth (reported in humans)
薬物相互作用
- CNS Depressants · Additive CNS depression if used concurrently with cetirizine · minor
モニタリング
- Clinical efficacy (reduction in pruritus or allergic signs)
- Adverse effects (vomiting, hypersalivation, somnolence)
過量投与
Cetirizine generally has a wide margin of safety. * **Massive Overdose**: May cross the blood-brain barrier in overdose situations, leading to neurologic signs (hyperactivity or severe sedation). * **Cardiovascular Safety**: Unlike earlier non-sedating antihistamines (terfenadine and astemizole), cetirizine does not appreciably prolong the QT interval on ECG at high serum levels. * > **TOXICITY ALERT**: Overdoses of cetirizine products that also contain pseudoephedrine (e.g., Zyrtec-D 12 Hour) are highly dangerous and potentially fatal. Immediate veterinary intervention and consultation with an animal poison control center are required.
VetSheet の薬剤リファレンスは、獣医療従事者向けの臨床意思決定支援を目的としており、専門的判断やメーカーの最新添付文書に代わるものではありません。