シプロヘプタジン
シプロヘプタジンは、強力な抗セロトニン作用を持つ第一世代の抗ヒスタミン薬です。獣医療においては、抗ヒスタミン作用よりも、その他の副次的な作用（適応外使用）を目的として頻繁に利用されます。 **主な獣医療での用途:** * **食欲増進剤:** 歴史的に猫の第一選択の食欲増進剤として使用されてきましたが、現代の臨床ではミルタザピンやカプロモレリンに取って代わられつつあります。しかし、他の選択肢が利用できない場合や禁忌の場合には、依然として有効な代替薬です。 * **セロトニン症候群の解毒剤:** 犬や猫におけるセロトニン毒性（例：ヒト用のSSRI/SNRIや5-HTPサプリメントの誤飲）に対する**標準的**な補助治療薬です。 * **馬の医療:** 馬の光原性ヘッドシェイキング（photic head shaking）の管理や、下垂体中葉機能障害（PPID / 馬クッシング症候群）の二次選択薬または補助療法として使用されます（ただし、PPIDにはペルゴリドの方がはるかに優れています）。 * **猫の喘息および瘙痒症:** 猫の好酸球性気道炎症やアレルギー性皮膚疾患に時折使用されますが、臨床的な有効性は限定的です。 > **臨床上のポイント:** シプロヘプタジンは肝臓で代謝され、腎臓から排泄されます。慢性腎臓病（CKD）の猫では用量の調整が推奨されます。
作用機序: Cyproheptadine exhibits a multi-receptor antagonism profile: * **Serotonin (5-HT) Antagonism:** Competitively binds to **5-HT2A receptors** in the hypothalamus → blocks serotonin-induced satiety → stimulates appetite. In serotonin syndrome, blocking these receptors reverses life-threatening neuromuscular and autonomic hyperactivity. * **Histamine (H1) Antagonism:** Competes with histamine for **H1-receptors** on effector cells → prevents histamine-mediated capillary permeability, smooth muscle spasm, and pruritus. It does *not* prevent histamine release. * **Anticholinergic Activity:** Weakly antagonizes **muscarinic receptors** → leads to common side effects like dry mouth and urinary retention. * **Calcium Channel Blockade:** Exhibits mild calcium channel blocking properties, which may contribute to its efficacy in equine photic head shaking.
動物種別の用量
- As an appetite stimulant · 2-4 mg per cat · PO · once or twice daily
- As an appetite stimulant · 1-4 mg/cat, or 0.35-1 mg/kg · PO · once or twice a day
- As an appetite stimulant · 2 mg per cat · PO · q12h
- As an appetite stimulant · 0.35-1 mg/kg · PO · q12h · May be dosed less frequently if inappetence is mild.
- As an appetite stimulant in cats with renal insufficiency · 1 mg per cat · PO · q12h
- As an antihistamine/antipruritic · 2 mg per cat · PO · q12h
- As an antihistamine/antipruritic · 2 mg per cat or 1.1 mg/kg · PO · q12h
- For feline asthma · 2 mg · PO · q12h · Particularly when cats are maxed out on dosages of corticosteroids and terbutaline. Therapeutic response may not be seen for 4-7 days, but CNS depression can occur in 24 hours.
- For adjunctive treatment of serotonin syndrome · 2-4 mg (total dose) · PO · q4-6h · until signs have resolved · In cases where PO dosing not possible (severe vomiting), may crush tablets and mix with saline and give rectally.
- Management of allergic disease / Appetite stimulation / Aortic thromboembolism · 0.1-0.5 mg/kg · PO · q8-12h
投与経路
禁忌
- Hypersensitivity to cyproheptadine
- Prostatic hypertrophy
- Bladder neck obstruction
- Severe cardiac failure
- Angle-closure glaucoma
- Pyeloduodenal obstruction
- Urinary retention (relative)
- Angle-closure glaucoma (relative)
- Pyloroduodenal obstruction (relative)
有害事象
- Sedation / CNS depression
- Paradoxical hyperexcitability or agitation (especially in cats)
- Anticholinergic effects (dry mucous membranes, urinary retention, tachycardia)
- Hemolytic anemia in cats (rare)
- Polyphagia (in dogs at higher doses)
- Mild depression, anorexia, or lethargy (in horses)
- Mild sedation
- Polyphagia
- Weight gain
- Reduced seizure threshold
薬物相互作用
- CNS Depressants (barbiturates, tranquilizers, etc.) · Additive CNS depression
- SSRIs (sertraline, fluoxetine, paroxetine, etc.) · Cyproheptadine may decrease the efficacy of the SSRI due to its serotonin antagonist properties
モニタリング
- Clinical efficacy (e.g., body weight if used for anorexia, resolution of neurologic signs if used for serotonin syndrome)
- Adverse effects (sedation, anticholinergic signs)
- Serum BUN/Creatinine in cats with long-term use
- Appetite and weight gain
- Resolution of allergic signs
- Neurological status (seizure activity)
過量投与
There are no specific antidotes available for cyproheptadine overdose. **Clinical Signs of Toxicity:** * Extensions of pharmacological effects: profound CNS depression (though paradoxical CNS stimulation/seizures may occur). * Severe anticholinergic effects: extreme drying of mucous membranes, tachycardia, urinary retention, hyperthermia. * Hypotension. **Management:** * **Decontamination:** Standard gut emptying protocols (emesis/activated charcoal) if caught early and patient is stable. * **Supportive Care:** IV fluids for hypotension, temperature regulation. * **Specific Interventions:** Physostigmine may be considered for life-threatening central anticholinergic effects. Diazepam should be employed to treat seizures if they occur. > *Note: Horses receiving 2x the recommended dose apparently showed no untoward effects.*
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。