ミルタザピン
ミルタザピンは非定型四環系抗うつ薬であり、獣医療においては主に犬や猫の強力な**食欲増進剤**および**制吐薬**として広く使用されています。 * **臨床上のポイント**: 慢性腎臓病（CKD）、うっ血性心不全、消化器疾患、肝疾患、または腫瘍の患者に特に有益であり、吐き気と食欲不振の両方を改善します。 * 難治性の嘔吐や化学療法誘発性の悪心・嘔吐（CINV）に対して、他の制吐薬と安全に併用できます。 * 主な用量制限となる副作用は鎮静ですが、猫では逆説的な興奮（鳴き声の増加、甘えん坊になるなど）が頻繁に観察されます。 > **重要**: 鎮静作用を最小限に抑えるため、常に最低有効量を使用してください。犬では1日30mgを超えないようにしてください。高用量では逆説的に食欲増進効果が失われます。
作用機序: Mirtazapine has a complex, multi-receptor pharmacological profile (often classified as a NaSSA - Noradrenergic and Specific Serotonergic Antidepressant): * **Central pre-synaptic α2-adrenergic receptors**: Antagonism blocks the negative feedback loop → **increases Norepinephrine (NE)** release → stimulates appetite via other α-receptors. * **5-HT3 receptors**: Potent antagonism in the Chemoreceptor Trigger Zone (CRTZ) and GI tract → provides robust **anti-nausea and antiemetic** effects. * **5-HT2 receptors**: Antagonism contributes to its anxiolytic profile. * **H1 (Histamine) receptors**: Potent antagonism → produces prominent **sedative effects**. * **Peripheral α1-adrenergic & Muscarinic receptors**: Moderate antagonism → may cause occasional orthostatic hypotension and mild anticholinergic effects.
動物種別の用量
- As an appetite stimulant and/or antiemetic · 3.75 mg (¼ of a 15 mg tablet) · PO · q72h (every 3 days)
- As an appetite stimulant and/or antiemetic · 3 mg per cat · PO · q72h (every 3 days)
- As an appetite stimulant and/or antiemetic · 3-4 mg per cat · PO · q72h (every 3 days)
- Appetite stimulation · 1.9 mg/cat · PO · q48h · Can double dose if needed or increase frequency to q24h but not both.
- As an appetite stimulant and/or antiemetic · 0.6 mg/kg · PO · q24h · Not to exceed 30 mg per day for appetite stimulation
- As an appetite stimulant and/or antiemetic · >75 lb. = 15 mg PO q12h or 30 mg PO q24h (once daily) · PO · q12h or q24h
- Appetite stimulation / Management of social fears · 1.1-1.3 mg/kg · PO · q24h · Anecdotal use for social fears.
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 mirtazapine
- Use of monoamine oxidase inhibitors (MAOIs, e.g., selegiline) within the past 14 days
- Pre-existing haematological disease
有害事象
- Drowsiness/sedation
- Vocalization (especially in cats)
- Increased affection (cats)
- Hypotension
- Tachycardia
- Sedation (common and can be profound)
- Increased vocalization (especially in cats)
- Altered behavior and increased interaction with others
- Blood dyscrasias (reported in humans)
薬物相互作用
- CLONIDINE · Mirtazapine may cause increases in blood pressure
- DIAZEPAM (and other benzodiazepines) · Minimal effects on mirtazapine blood levels, but may cause additive impairment of motor skills
- FLUVOXAMINE · May cause increased serum concentrations of mirtazapine
- LINEZOLID · Increased risk for serotonin syndrome
- SELEGILINE, AMITRAZ · Increased risk for serotonin syndrome; MAO inhibitors considered contraindicated with mirtazapine
- TRAMADOL · Increased risk for serotonin syndrome
- Other behaviour-modifying drugs (e.g., SSRIs, MAOIs) · Increased risk of serotonin syndrome · major
モニタリング
- Increased appetite
- Decreased episodes of vomiting
- Weight gain
- Adverse effects (sedation, vocalization, tachycardia)
- Appetite and body weight
- Behavioral changes (sedation, vocalization)
- Complete blood count (due to human risk of blood dyscrasias)
- Hepatic and renal function parameters
過量投与
Ingestion of upwards of 10-fold to 30-fold the therapeutic dose in humans exhibits minimal toxicity requiring no acute intervention other than observation. > **Treatment**: Despite the wide safety margin, standard overdose protocols (including the administration of **activated charcoal**) and monitoring are recommended in acute overdose situations.
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。