トラマドール
トラマドールは、主に軽度から中等度の疼痛管理に使用され、時には鎮咳薬としても使用される、合成の中枢性**オピオイド様鎮痛薬**です。 **主な臨床的特徴：** * 弱い**μ-オピオイド受容体作動薬**として働き、**セロトニン**および**ノルアドレナリン**の再取り込みを阻害します。 * 変形性関節症やがんなどの慢性疼痛に対する**マルチモーダル鎮痛プロトコル**（NSAIDs、ガバペンチン、アマンタジンなどとの併用）の一部として非常に有用です。 * 慢性疼痛状態において、完全な鎮痛効果が得られるまでに最大**2週間**かかる場合があります。 * **臨床のポイント：** モノグラフには米国では規制薬物ではないと記載されていますが、ヒトでの乱用の可能性があるため、**米国DEAは2014年にトラマドールをスケジュールIVの規制物質に再分類しました**。 * 犬では一般的に忍容性が高く、鎮静が最も一般的な副作用です。猫では不快感（dysphoria）を経験することがあり、薬の嗜好性が非常に悪いです。
作用機序: Tramadol provides analgesia through a dual mechanism of action: 1. **Opioid Activity:** Tramadol and its active metabolite **O-desmethyltramadol (M1)** bind to **mu-opioid receptors** in the central nervous system. 2. **Monoaminergic Activity:** It inhibits the synaptic reuptake of **serotonin (5-HT)** and **norepinephrine (NE)** → enhancing descending inhibitory pathways of pain transmission in the spinal cord. **Pharmacologic Pearl:** The M1 metabolite is 6 times more potent as an analgesic and has 20 times greater affinity for mu-receptors than the parent drug. Dogs produce very little of the M1 metabolite compared to cats and humans, which explains why tramadol's opioid-mediated efficacy in dogs is often erratic and heavily reliant on its serotonin/norepinephrine reuptake inhibition. Naloxone only partially antagonizes tramadol's analgesic effects.
動物種別の用量
- Starting dose · 2 mg/kg twice daily · PO · q12h · Based upon the pharmacokinetics of tramadol and ODT in cats.
- Current dosing recommendations · 1-2 mg/kg PO q12h · PO · q12h · Maximum analgesic effects may be delayed up to 14 days for chronic pain.
- Chronic pain · 1-4 mg/kg PO 2-3 times a day · PO · q8-12h · Reasonable for mild pain; dose and interval may need adjustment for more severe pain.
- Analgesia · 2-4 mg/kg · PO · q8h · Oral preparations are highly unpalatable to cats. Watch for dysphoria.
- Analgesia · 1-2 mg/kg · IV · as needed
- Analgesia · 1-2 mg/kg · SC · as needed
- Chronic laminitis pain · 5 mg/kg PO twice daily for seven days, alone or with ketamine at 0.6 mg/kg/hr IV during six hours each day for the first 3 days of treatment · PO/IV · q12h · 7 days · Pain relief was enhanced.
- General/Non-responsive pain · 5 mg/kg PO q6-8h and up to 10 mg/kg PO q6-8h · PO · q6-8h · Maximum analgesic effects may not occur immediately and may be delayed up to 14 days for chronic pain conditions.
- Analgesic · 2-5 mg/kg four times daily · PO · q6h · Suggested starting dose.
投与経路
禁忌
- Hypersensitivity to tramadol or other opioids
- Combination products containing acetaminophen (e.g., Ultracet) are STRICTLY CONTRAINDICATED in cats
- Concurrent use with MAOIs (e.g., selegiline, amitraz) due to risk of serotonin syndrome
- Patients with a history of epilepsy or seizure disorders
- Concurrent use with MAOIs
有害事象
- Dogs: Excessive sedation, agitation, anxiety, tremor, dizziness
- Dogs: Inappetence, vomiting, constipation, diarrhea
- Cats: Dysphoria, mydriasis, dose avoidance (unpalatability)
- Humans: Pruritus (approx. 10%)
- Injectable form: Respiratory and cardiac depression
- Sedation (especially at high doses in dogs)
- Dysphoria (more likely in cats)
- Nausea
- Behavioral changes
- Increased risk of seizures
薬物相互作用
- Digoxin · Rarely linked to digoxin toxicity in humans.
- MAO Inhibitors (amitraz, selegiline) · Potential for fatal serotonin syndrome; concurrent use should be avoided.
- Ondansetron · May reduce the effectiveness of both drugs.
- Quinidine · May increase tramadol concentrations and decrease M1 (active metabolite) concentrations.
- SAMe (S-adenosylmethionine) · Theoretically could cause additive serotonergic effects.
- Sevoflurane · Pretreatment with tramadol reduced MAC values by approximately 30% in dogs and 40% in cats.
- SSRI Antidepressants (fluoxetine, sertraline, paroxetine) · Can inhibit the metabolism of tramadol to its active metabolites, decreasing efficacy and increasing the risk of toxicity (serotonin syndrome, seizures).
- Tricyclic Antidepressants (clomipramine, amitriptyline) · Increased risk for seizures; amitriptyline may inhibit tramadol metabolism.
- Warfarin · Increased PT and INR reported in humans (relatively rare).
- Amitriptyline · Increased risk of serotonin syndrome · major
- Selegiline · Increased risk of serotonin syndrome · major
- SSRIs (e.g., Fluoxetine) · Increased risk of serotonin syndrome · major
モニタリング
- Clinical efficacy (pain scoring, mobility, comfort levels)
- Adverse effects (excessive sedation, GI upset, dysphoria, agitation)
- Pain scores to assess efficacy
- Signs of sedation or dysphoria
- Signs of serotonin syndrome (hyperthermia, hypertension, agitation, tremors)
- Seizure activity in susceptible individuals
過量投与
Acute oral overdoses may cause either **CNS depressive signs** or **serotonin syndrome**. * **Clinical Signs:** Lethargy, mydriasis, ataxia, and vomiting are most common. Stimulatory signs such as tachycardia, tremors, vocalization, agitation, and seizures may also occur. Cats frequently show mydriasis, hypersalivation, and tachycardia. * **Treatment:** Primarily supportive (maintaining respiration, treating seizures with benzodiazepines or barbiturates). * > **Important:** Naloxone may **NOT** be useful in tramadol overdoses. It only partially reverses effects and may actually **increase the risk of seizures**. Cyproheptadine and phenothiazines can be used to treat stimulatory signs (serotonin syndrome).
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。