アミトリプチリン
アミトリプチリンは第一世代の**三環系抗うつ薬 (TCA)**です。犬の原発性行動障害（分離不安など）の治療においては、クロミプラミンやSSRI（フルオキセチンなど）のような新しい薬剤に取って代わられつつありますが、獣医療においては依然として非常に汎用性の高い薬剤です。 **臨床のポイント**: そのマルチモーダルな受容体活性により、**神経障害性疼痛**、**そう痒症**（強力な抗ヒスタミン作用による）、および**猫特発性下部尿路疾患 (FLUTD/FIC)**の補助治療に特に有用です。また、鳥類の毛引き行動を管理するために使用されることもあります。
作用機序: Amitriptyline and its active metabolite, **nortriptyline**, exhibit a complex pharmacologic profile, affecting multiple receptor systems: * **Serotonin (SERT) & Norepinephrine (NET) Reuptake Inhibition**: Blocks the amine pump → increases synaptic levels of 5-HT and NE → mood stabilization and descending pain pathway modulation. * **H1-Receptor Antagonism**: Potent antihistamine effect → stabilizes mast cells and provides antipruritic action. * **M1-Muscarinic (Anticholinergic) Antagonism**: Causes smooth muscle relaxation (useful in FLUTD) but also leads to side effects like dry mouth and urine retention. * **Alpha-1 Adrenergic Antagonism**: Can cause mild vasodilation and sedation. * **NMDA Receptor & Sodium Channel Blockade**: Contributes to its efficacy in treating chronic, neuropathic pain.
動物種別の用量
- Adjunctive treatment of pruritus · 1-2 mg/kg PO q12h · PO · q12h
- Acral pruritic dermatitis · 2.2 mg/kg PO twice daily · PO · q12h · 2-4 week trial recommended · Only occasionally effective.
- Separation anxiety or generalized anxiety · 1-2 mg/kg PO q12h · PO · q12h · Use with behavior modification.
- Behavior disorders amenable to tricyclics · 1-4 mg/kg PO q12h. Begin at 1-2 mg/kg PO q12h for 2 weeks, increase by 1 mg/kg up to maximum dosage (4 mg/kg) as necessary. If no clinical response, decrease by 1 mg/kg PO q12h for 2 weeks until at initial dosage. · PO · q12h
- Behavior disorders amenable to tricyclics · 2.2-4.4 mg/kg PO q12h · PO · q12h
- Behavior disorders amenable to tricyclics · 0.25-1.5 mg/kg PO every 12-24h · PO · q12-24h
- Neuropathic pain · 1-2 mg/kg PO q12-24h · PO · q12-24h
- Adjunctive treatment of pain associated with appendicular osteosarcoma · 1-2 mg/kg PO q12-24h · PO · q12-24h
- Management of chronic anxiety, compulsive disorders, and separation anxiety · 1-2 mg/kg · PO · q12-24h · Clomipramine is an authorized preparation for dogs and is claimed to have better anticompulsive properties.
- Adjunctive treatment of feather plucking · 1-2 mg/kg PO q12-24 hours. Anecdotal reports indicate some usefulness. Barring side-effects, may be worth a more prolonged course of therapy to determine efficacy. · PO · q12-24h · Prolonged course
投与経路
禁忌
- Prior sensitivity to any tricyclic antidepressant
- Concomitant use with monoamine oxidase inhibitors (MAOIs)
有害事象
- Sedation
- Constipation
- Urinary retention
- Hyperexcitability (dogs)
- Seizures (rare)
- Cardiac dysrhythmias
- Bone marrow suppression
- Vomiting
- Diarrhea
- Hypersalivation (cats)
- Anorexia (cats)
- Thrombocytopenia
- Neutropenia
- Unkempt hair coat (cats)
- Ataxia
- Disorientation
薬物相互作用
- Anticholinergic agents · Increased effects; hyperthermia and ileus possible
- Cimetidine · May inhibit tricyclic antidepressant metabolism and increase the risk of toxicity · moderate
- Cisapride · May have additive effects on QTc interval; possible serious arrhythmias may result
- Monoamine Oxidase Inhibitors (selegiline, amitraz) · Potential life-threatening serotonin syndrome; use together not recommended
- CNS Depressants · Increased sedative effects
- Diazepam · Possible increased amitriptyline levels · moderate
- Quinidine · Increased risk for QTc interval prolongation and tricyclic adverse effects
- Selective-Serotonin Re-uptake Inhibitors (SSRIs, fluoxetine) · Potential increased amitriptyline levels, increased risk for serotonin syndrome; enhanced monitoring suggested if used together
- Sympathomimetic agents · May increase the risk of cardiac effects (arrhythmias, hypertension, hyperpyrexia)
- Thyroid agents · Increased risk for arrhythmias; monitor closely
- Monoamine oxidase inhibitors (MAOIs) · Risk of fatal serotonin syndrome. Requires a minimum 2-week washout period. · major
- Chlorphenamine · Metabolized by CYP2D6; may alter amitriptyline metabolism. · moderate
モニタリング
- Clinical efficacy (behavior, pain, or pruritus improvement)
- Adverse effects
- Baseline cardiac evaluation (ECG) prior to therapy
- Baseline CBC and serum chemistry panel prior to therapy
- Liver enzymes in cats (prior to therapy, 1 month after initial therapy, and yearly thereafter)
過量投与
Overdosage with tricyclics can be **life-threatening** (arrhythmias, cardiorespiratory collapse). Because toxicities and therapies are complicated, it is recommended to contact an animal poison control center immediately in any potential overdose situation. * **Dogs**: Common findings include lethargy and tachycardia. * **Cats**: Common findings include vocalization, ataxia, mydriasis (dilated pupils), tachycardia, disorientation, lethargy, and agitation.
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。