曲馬多
曲馬多是一種合成的中樞作用**類鴉片鎮痛藥**，主要用於控制輕至中度疼痛，偶爾也作為鎮咳藥使用。 **主要臨床重點：** * 作為弱的 **mu-鴉片受體促效劑**，並能抑制**血清素**和**去甲腎上腺素**的再攝取。 * 在慢性疼痛（如骨關節炎或癌症）的**多模式鎮痛方案**中非常有用（例如與 NSAIDs、加巴噴丁或金剛烷胺合併使用）。 * 在慢性疼痛狀態下，可能需要長達**兩週**的時間才能達到完全的鎮痛效果。 * **臨床提示：** 雖然藥典指出其在美國非管制藥物，但由於人類濫用的潛力，**美國 DEA 已於 2014 年將曲馬多重新分類為第四級管制物質 (Schedule IV)**。 * 在狗中通常耐受性良好，最常見的副作用是鎮靜。貓可能會出現煩躁不安（dysphoria），且對此藥物的適口性極差。
作用機制: 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.
各物種劑量
- 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.
給藥途徑
禁忌症
- 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
不良反應
- 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
藥物相互作用
- 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
監測
- 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
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).
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