レミフェンタニル
**レミフェンタニル**は、フェンタニルに構造が類似した強力かつ超短時間作用型の合成**μ-オピオイド作動薬**です。獣医療においては、主に全身麻酔時の鎮痛補助薬として、特に全静脈麻酔（TIVA）プロトコルで利用されます。 主な薬理学的特徴： * **臓器非依存性代謝**：肝代謝や腎排泄に依存する他の多くのオピオイドとは異なり、血漿、赤血球、組織中の非特異的エステラーゼによって急速に分解されます。そのため、重度の肝機能または腎機能障害を持つ患者に対しても非常に安全です。 * **急速な作用消失**：作用時間が極めて短いため、持続点滴の期間に関わらず、迅速かつ予測可能な覚醒が得られ、他のオピオイドで見られるような長時間の鎮静を最小限に抑えます。 * **天井効果**：麻酔補助薬として使用される他のオピオイドと同様に、用量を増やしても鎮痛効果は増強されず、副作用のリスクのみが高まる天井効果を示します。 > **臨床上のポイント**：点滴を中止すると術後の残存鎮痛効果が全く得られないため、急性覚醒時せん妄や疼痛を防ぐために、レミフェンタニルの投与終了前に長時間作用型の鎮痛薬（NSAIDs、ブプレルノルフィン、局所神経ブロックなど）を投与することが不可欠です。
作用機序: Remifentanil acts as a selective agonist at **mu-opioid receptors** (G-protein coupled receptors) located primarily in the pain-regulating areas of the central nervous system (limbic system, spinal cord, thalamus, midbrain). **Mechanism Pathway**: Remifentanil binds to **mu-receptors** → inhibits adenylate cyclase → decreases intracellular cAMP → promotes opening of potassium channels and inhibits voltage-gated calcium channels → hyperpolarization of nociceptive neurons → suppression of substance P release and profound analgesia. **Metabolism**: It is rapidly metabolized via hydrolysis of its propanoic acid-methyl ester linkage by **nonspecific blood and tissue esterases** (not plasma pseudocholinesterase). The principal carboxylic acid metabolite (GR90291) is virtually inactive (4000 times less potent in dogs).
動物種別の用量
- Analgesic adjunct to general anesthesia · 0.2 micrograms/kg/minute (for OHE) to 0.3 micrograms/kg/minute (to reduce stimulus-induced movement) · IV · CRI · In propofol-anesthetized (0.3 mcg/kg/min) cats.
- Analgesic adjunct to general anesthesia · 4 micrograms/kg bolus IV, followed by 6-20 micrograms/kg/hr CRI. · IV · CRI · Do not confuse mcg/kg/hr with mcg/kg/min.
- Analgesic adjunct to general anesthesia · 1 microgram/kg IV loading dose slowly over 2-3 minutes, followed by a 0.1-0.2 microgram/kg/minute CRI. · IV · CRI · Do not confuse mcg/kg/hr with mcg/kg/min.
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 remifentanil or other fentanyl analogs
- Epidural or intrathecal administration (contraindicated due to the presence of glycine in the formulation)
有害事象
- Respiratory depression
- Apnea
- Bradyarrhythmias
- Hypotension
- Hyperthermia (noted in cats)
- Anaphylaxis (rare)
薬物相互作用
- CNS Depressants (e.g., propofol, isoflurane, thiopental) · Additive CNS and respiratory depression; remifentanil significantly reduces MAC and induction agent requirements.
- Diuretics · Opiates may decrease diuretic efficacy in patients with congestive heart failure.
- Monoamine Oxidase Inhibitors (e.g., amitraz, selegiline) · Severe and unpredictable opiate potentiation may occur; use is generally not recommended if an MAOI has been used within 14 days.
- Skeletal Muscle Relaxants · Remifentanil may enhance neuromuscular blockade.
- Nitrous Oxide · High doses of remifentanil combined with nitrous oxide may cause cardiovascular depression.
- Tricyclic Antidepressants (e.g., clomipramine, amitriptyline) · May exacerbate the effects of tricyclic antidepressants.
- Warfarin · Opiates may potentiate anticoagulant activity.
モニタリング
- Cardiac rate and rhythm (ECG)
- Respiratory rate and depth / Capnography (ETCO2)
- Pulse oximetry (SpO2) or arterial blood gas
- Blood pressure (direct or indirect)
- Body temperature (especially in cats)
過量投与
Overdosage manifests as an enhancement of the drug's pharmacological effects. **Clinical Signs**: * Apnea and severe respiratory depression * Chest-wall rigidity * Hypoxemia * Hypotension and severe bradycardia * Seizures **Treatment**: 1. **Discontinue drug administration immediately.** 2. Provide supportive therapy, primarily **mechanical ventilation** and oxygen administration. Because the drug is cleared so rapidly by tissue esterases, this is often the only intervention required. 3. Administer IV fluids, and use **glycopyrrolate or atropine** to manage bradycardia or hypotension. 4. **Naloxone** may be used to reverse mu-opioid activity, but caution is advised as it can lead to acute pain and sympathetic hyperactivity.
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。