右美托咪啶
> **右美托咪啶 (Detomidine)** 是一種強效的 α-2 腎上腺素受體激動劑，主要在馬匹醫學中用於提供深度的鎮靜與鎮痛效果。 * **效力：** 其效力約為甲苯噻嗪 (Xylazine) 的 50 到 100 倍。 * **臨床應用：** 廣泛用於馬匹的站立鎮靜、小型外科手術及鎮痛（特別是疝痛）。也曾標示外用於牛、小型反芻動物、駱駝科動物及鳥類。 * **重要注意事項：** 即使馬匹看起來已深度鎮靜，仍可能對外界刺激產生突然反應（例如踢腿）。併用鴉片類藥物（如布托啡諾）有助於緩和這種驚嚇反應並提升鎮靜品質。
作用機制: Detomidine acts as a potent and highly specific agonist at **alpha-2 adrenergic receptors** in the central and peripheral nervous systems. * **Sedation & Analgesia:** Activation of presynaptic alpha-2 receptors in the locus coeruleus and dorsal horn of the spinal cord → inhibition of norepinephrine release → decreased sympathetic outflow, resulting in profound sedation, muscle relaxation, and analgesia. * **Cardiovascular Effects:** Initial activation of peripheral postsynaptic alpha-2 receptors → transient vasoconstriction and **hypertension** → compensatory vagal reflex → profound **bradycardia** and potential AV block. Central sympatholytic effects then lead to a prolonged decrease in blood pressure.
各物種劑量
- Anesthesia · 0.01 mg/kg IM · IM · once · Followed by propofol at 3-5 mg/kg IV.
- Analgesia · 0.005-0.05 mg/kg IV or IM q3-6 hours (once) · IV/IM · q3-6h · once
- Anesthesia · 0.01 mg/kg IM · IM · once · Followed by propofol at 3-5 mg/kg IV.
- Analgesia · 0.005-0.05 mg/kg IV or IM q3-6 hours (once) · IV/IM · q3-6h · once
- Sedation/analgesia · 30-60 micrograms/kg (0.03-0.06 mg/kg) IV or IM · IV/IM · once · Not FDA-approved.
- Analgesia · 0.01 mg/kg IV · IV · once · 1/2 hour · Withdrawal times: Milk = 72 hours; Slaughter = 7 days.
- Sedation/analgesia · 20-40 micrograms/kg (0.02-0.04 mg/kg) IV or IM · IV/IM · once · IV only for analgesia. Lower dose provides 30-90 min sedation/30-45 min analgesia. Higher dose provides 90-120 min sedation/45-75 min analgesia.
- Sedation/analgesia (Sublingual Gel) · 0.04 mg/kg (0.018 mg/lb) (0.040 mg/kg) placed beneath the tongue · Sublingual · once · Not meant to be swallowed.
- Marked abdominal pain (not surgical candidates or long transport) · 0.01-0.02 mg/kg (10-20 micrograms/kg) IV or IM · IV/IM · once
給藥途徑
禁忌症
- Preexisting AV or SA heart block
- Severe coronary insufficiency
- Cerebrovascular disease
- Severe respiratory disease
- Chronic renal failure
不良反應
- Initial blood pressure increase (hypertension)
- Profound bradycardia and heart block (AV block)
- Piloerection
- Sweating
- Ataxia
- Salivation
- Slight muscle tremors
- Penile prolapse
- Decreased gastrointestinal motility
藥物相互作用
- Other Alpha-2 Agonists (e.g., xylazine, medetomidine, clonidine) · Not recommended to be used together as effects may be additive.
- Anesthetics, Opiates, Sedative/Hypnotics · Effects may be additive; dosage reduction required. Increased risk for arrhythmias with thiopental, ketamine, or halothane.
- Epinephrine · Do not use to treat cardiac effects caused by detomidine, as epinephrine possesses alpha agonist effects.
- Phenothiazines (e.g., acepromazine) · Severe hypotension can result.
- Potentiated Sulfonamides (e.g., trimethoprim/sulfa) · Fatal dysrhythmias may occur if used with intravenous potentiated sulfonamides.
監測
- Level of sedation and analgesia
- Cardiac rate and rhythm
- Blood pressure (if indicated)
過量
> **Toxicity Profile:** * Tolerated by horses at 5X the high dose level (0.2 mg/kg). * Doses of 10-40X recommended can cause severe respiratory and cardiovascular changes that can become irreversible and cause death. * **Reversal:** Alpha-2 antagonists such as **atipamezole** (50-100 micrograms/kg) or **yohimbine** can be successfully used to reverse some or all effects of inadvertent overdoses.
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