ロラタジン
**ロラタジン**は、第2世代の非鎮静性H1受容体拮抗薬であり、獣医療では主にアトピー性皮膚炎、ワクチン反応、虫刺されなどのアレルギー疾患の管理に使用されます。第一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、血液脳関門を容易に通過しないため、中枢神経系の抑制や鎮静の発生率が大幅に低下します。 > **臨床上の警告：** 人間用の市販ロラタジン製品に充血除去薬（**プソイドエフェドリン**など、「Claritin-D」と表記されることが多い）が含まれていないことを必ず確認してください。プソイドエフェドリンは犬や猫に対して非常に毒性が高く、致命的な心血管系および神経系の刺激を引き起こす可能性があります。
作用機序: Loratadine acts as a selective inverse agonist/antagonist at peripheral **H1 histamine receptors**. * **Histamine Blockade:** It competitively binds to H1 receptors on effector cells in the gastrointestinal tract, blood vessels, and respiratory tract → prevents histamine from binding and exerting its pro-inflammatory and vasodilatory effects. * **Non-sedating:** Due to its lipophobic nature and large molecular size, it has poor penetration across the blood-brain barrier, resulting in minimal to no central H1 receptor blockade.
投与経路
禁忌
- Known hypersensitivity to loratadine or desloratadine
- Use with caution in patients with severe hepatic impairment
- Use with caution in patients with keratoconjunctivitis sicca (dry eye)
有害事象
- Mild lethargy or sedation (rare compared to first-generation antihistamines)
- Vomiting
- Diarrhea
- Dry mouth (xerostomia)
- Decreased tear production
薬物相互作用
- Ketoconazole · May inhibit the metabolism of loratadine, increasing plasma concentrations · moderate
- Erythromycin · May inhibit the metabolism of loratadine, increasing plasma concentrations · moderate
- Cimetidine · May inhibit the metabolism of loratadine, increasing plasma concentrations · moderate
- Amiodarone · May increase loratadine levels via CYP inhibition · moderate
モニタリング
- Resolution of allergic clinical signs (e.g., reduced pruritus, erythema)
- Adverse gastrointestinal effects
- Tear production (Schirmer Tear Test) if dry eye is suspected
過量投与
Loratadine has a wide margin of safety. Massive overdosage may cause tachycardia, somnolence, and headache. **Treatment:** Consists of standard gastrointestinal decontamination (emesis induction, activated charcoal) if ingestion is recent, followed by symptomatic and supportive care. Loratadine is not significantly removed by hemodialysis.
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。