クレンブテロール
**クレンブテロール（Clenbuterol）**は、強力で長時間作用型の**β2アドレナリン受容体作動薬**であり、獣医学においては主に馬の気管支拡張薬として、**反復性気道閉塞（RAO）**（以前の慢性閉塞性肺疾患（COPD）または「喘鳴症」）などの気道閉塞性疾患の管理に使用されます。 呼吸器系への応用に加え、牝馬の難産管理を補助するための**子宮弛緩薬（子宮収縮抑制薬）**として使用されることもあります。 ### 臨床上の重要なポイント： * **食肉用動物への使用厳禁**：クレンブテロールは高用量で再分配作用（筋肉量を増やし脂肪を減らす）を示します。汚染された肉を摂取した人間に重篤な**リレー毒性**（激しい振戦、頻脈、入院を要する事態）を引き起こすことが十分に証明されているため、食肉生産動物への使用は世界的に厳しく禁止されています。 * **乱用の可能性**：そのアナボリック（同化）様作用のため、人間のボディビルやダイエット目的で頻繁に乱用されます。獣医師は薬物の横流しに警戒する必要があります。 * **内分泌および心臓への影響**：馬への長期投与は、有酸素運動能力の低下、心肥大、心筋へのコラーゲン浸潤、および免疫機能の変化を引き起こす可能性があります。
作用機序: Clenbuterol selectively binds to and activates **beta-2 adrenergic receptors** on smooth muscle cells. ### Primary Pathway: **Beta-2 Receptor Activation** → Stimulates **G_s proteins** → Activates **Adenylyl Cyclase** → Increases intracellular **cyclic AMP (cAMP)** → Activates **Protein Kinase A (PKA)** → Decreases intracellular calcium concentrations → Results in **smooth muscle relaxation** (bronchial, vascular, and uterine). ### Secondary Mechanisms: * **Anti-inflammatory Effects**: Inhibits the release of pro-inflammatory cytokines (such as **Interleukin-1β** and **Tumor Necrosis Factor-α**) from pulmonary macrophages. * **Mucociliary Clearance**: Increases ciliary beat frequency in the respiratory tract, enhancing the clearance of excessive mucus associated with RAO.
動物種別の用量
- Bronchodilator · Initially, 0.8 micrograms/kg (practically: 0.5 mL of the commercially available syrup/100 lb. BW) twice daily for 3 days; if no improvement increase to 1.6 micrograms/kg (practically: 1 mL of the commercially available syrup/100 lb. BW) twice daily for 3 days; if no improvement increase to 2.4 micrograms/kg (practically: 1.5 mL of the commercially available syrup/100 lb. BW) twice daily for 3 days; if no improvement increase to 3.2 micrograms/kg (practically: 2 mL of the commercially available syrup/100 lb. BW) twice daily for 3 days; if no improvement discontinue therapy. · PO · q12h · Recommended duration of therapy is 30 days; then withdraw therapy and reevaluate. · ARCI UCGFS Class 3 Drug
- Adjunctive treatment for dystocia emergencies · 300 micrograms per 500 kg mare IV slowly · IV · Single dose · Parenteral formulation not available commercially in the USA. Fast onset allows quick decision if uterine relaxation will correct the problem. May be used with sedatives/analgesics; xylazine or detomidine may potentiate uterine relaxant effects.
- Adjunctive treatment for dystocia emergencies · 10 mls of clenbuterol syrup orally as the mare walks in the door. · PO · Single dose · Author's hospital protocol upon arrival of a dystocia.
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
- Food-producing animals (strictly banned by law)
- Horses suspected of having cardiovascular impairment
- Pregnant mares near full-term (unless used specifically for dystocia management)
有害事象
- Muscle tremors
- Sweating
- Restlessness
- Urticaria
- Tachycardia
- Creatine kinase (CK) elevations
- Ataxia (rare)
- Abortion in pregnant animals
- Cardiac hypertrophy and collagen infiltration (with chronic use)
薬物相互作用
- Inhalant Anesthetics (halothane, isoflurane, methoxyflurane) · May predispose the patient to ventricular arrhythmias, particularly with preexisting cardiac disease.
- Beta-Blockers (e.g., propranolol) · May antagonize clenbuterol's bronchodilating and tocolytic effects.
- Digoxin · May increase the risk of cardiac arrhythmias.
- Dinoprost (Prostaglandin F2alpha) · Clenbuterol may antagonize the ecbolic effects of dinoprost.
- Oxytocin · Clenbuterol may antagonize the uterine contracting effects of oxytocin.
- Other Sympathomimetic Amines (terbutaline, albuterol) · Concomitant administration may enhance the adverse cardiovascular and neurologic effects of clenbuterol.
- Tricyclic Antidepressants or MAOIs · May potentiate the vascular effects of clenbuterol.
モニタリング
- Clinical efficacy (improvement in respiratory rate, effort, and reduction of cough)
- Heart rate and rhythm (monitor for tachycardia or arrhythmias)
- Signs of muscle tremors, sweating, or restlessness
- Creatine kinase (CK) levels if myopathy is suspected
過量投与
Overdoses can cause severe sympathomimetic toxicity (extreme tachycardia, arrhythmias, severe muscle tremors, hypertension followed by hypotension, and hypokalemia). **Treatment**: * **Decontamination**: Emptying the gut (gastric lavage/activated charcoal) may be appropriate depending on the dosage and timing of ingestion. * **Medical Management**: Provide supportive therapy. Administration of parenteral **beta-blockers** (e.g., propranolol, esmolol) may be considered to control heart rate, rhythm, and elevated blood pressure.
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。