納曲酮
納曲酮是一種合成的長效**純鴉片類受體拮抗劑**。雖然結構上與納洛酮（naloxone）相似，但其口服生物利用度更高，作用時間更長。 在獸醫學中，它主要作為標示外用藥，用於**強迫性行為障礙**的輔助治療，例如： - 肢端舔舐性皮膚炎（舔舐肉芽腫） - 追尾行為 - 吸吮側腹行為 - 其他自我傷害或刻板行為 **臨床要點**：其應用於行為醫學的原理，源於刻板行為會刺激內源性鴉片類物質（腦內啡）釋放，進而強化該行為的假說。透過阻斷這些受體，納曲酮消除了內在的「獎勵」機制，有助於消除強迫行為。
作用機制: Naltrexone acts as a **competitive antagonist** at opioid receptors, with the highest affinity for **μ (mu)** receptors, followed by **κ (kappa)** and **δ (delta)** receptors. - **Mechanism in Behavior Disorders**: Compulsive behaviors → Release of endogenous endorphins → Binding to μ-receptors → Reinforcement/Analgesia. - Naltrexone **blocks** these receptors → Prevents endorphin binding → Eliminates the auto-reinforcing reward loop of the stereotypic behavior.
各物種劑量
- As adjunctive therapy in behavior disorders · 25-50 mg/cat · PO · q24h · Note: has a bitter taste
- As adjunctive therapy in behavior disorders (tail chasing or excessive licking) · 1-2 mg/kg · PO · daily · Long-term therapy may be required · First give 0.01 mg/kg SC of naloxone to determine if narcotic antagonists may be effective, if so give naltrexone.
- As adjunctive therapy in behavior disorders · 2-5 mg/kg · PO · once daily
- As adjunctive therapy in behavior disorders · 1-2.2 mg/kg · PO · q8-12h
- For the adjunctive treatment of acral pruritic dermatitis · 2.2 mg/kg · PO · once daily · one-month trial · Some dogs exhibit drowsiness and minor changes in behavior. 50-60% of patients have benefited. Expense is of concern.
劑量為持牌獸醫專業人員的臨床參考。請務必對照最新藥品說明書及個別病患確認。
給藥途徑
不良反應
- Drowsiness
- Minor changes in behavior
- Elevated hepatic enzymes (AST, ALT)
藥物相互作用
- Opioid partial-agonists (e.g., butorphanol, pentazocine, nalbuphine) · May antagonize the effects of these agents, including respiratory depression and analgesia.
- Clonidine · Naltrexone may reduce the hypotensive and bradycardic effects of clonidine.
- Yohimbine · Naltrexone may increase the CNS effects of yohimbine (anxiety, tremors, nausea, palpitations) and increase plasma cortisol levels.
監測
- Clinical efficacy (reduction in stereotypic behaviors)
- Liver enzymes (AST, ALT) if using very high doses with prolonged therapy
過量
Specific overdosage information is not provided in the monograph. However, as an opioid antagonist, massive overdoses could theoretically cause dysphoria or precipitate withdrawal in opioid-dependent patients. Monitor liver enzymes if very high doses are ingested.
VetSheet 藥物參考供持牌獸醫專業人員作臨床決策輔助之用,不能取代專業判斷或廠方最新藥品說明書。