エピネフリン
**エピネフリン**（一般にアドレナリンとして知られる）は、副腎髄質で産生される強力な内因性カテコールアミンです。交感神経系の主要な「闘争か逃走か」のホルモンです。 獣医学においては、主に以下の目的で使用される極めて重要な救命救急薬です： * **心肺脳蘇生法 (CPCR):** 心停止（心静止）時の自己心拍再開を促すため。 * **重度のアナフィラキシー:** 気管支拡張と血管収縮を誘発し、生命を脅かすアレルギー反応を急速に回復させるため。 * **局所麻酔の補助:** 局所麻酔薬（リドカインなど）に添加し、局所の血管収縮を引き起こすことで、全身への吸収を遅らせ、麻酔効果を延長し、部位の出血を減少させるため。 > **臨床上のポイント:** エピネフリンは非常に強力であり、治療域が非常に狭いです。正しい濃度が使用されていることを確認するために細心の注意を払う必要があります。**1:1,000 (1 mg/mL) の濃度と 1:10,000 (0.1 mg/mL) の濃度を絶対に混同しないでください。**
作用機序: Epinephrine is a direct-acting, non-selective adrenergic agonist that stimulates both alpha (α) and beta (β) receptors via G-protein coupled pathways (activating **adenylyl cyclase** → ↑ **cAMP**). * **α1-receptors:** → Induces profound smooth muscle contraction and vasoconstriction, increasing systemic vascular resistance and blood pressure. * **β1-receptors:** → Directly stimulates the heart, increasing both chronotropy (heart rate) and inotropy (contractility), which increases cardiac output and myocardial oxygen demand. * **β2-receptors:** → Relaxes smooth muscle, leading to profound bronchodilation (relieving bronchospasm in anaphylaxis), vasodilation in skeletal muscle, and increased glycogenolysis (raising blood sugar). * **Histamine Antagonism:** Physiologically antagonizes the effects of histamine released during anaphylaxis. *Hemodynamic effects depend on the route and rate of administration:* Rapid IV injection causes direct cardiac stimulation and increased systolic BP. Slow IV infusion produces a modest rise in systolic pressure, a decrease in diastolic pressure, and decreased total peripheral resistance due to dominant β2 effects.
動物種別の用量
- Anaphylaxis · 0.5-1 mL/100 lbs. body weight of 1:1,000 (dilute to 1:10,000 if using IV) · SC, IM, IV · may be repeated at 15 minute intervals · Often used in conjunction with corticosteroids and diphenhydramine.
- Anaphylaxis · 0.5-1 mL/100 lbs. body weight of 1:1,000 (dilute to 1:10,000 if using IV) · SC, IM, IV · may be repeated at 15 minute intervals · Often used in conjunction with corticosteroids and diphenhydramine.
- Cardiac resuscitation (asystole) · 0.01 mg/kg · IV · Repeat every 3-5 minutes if no return of spontaneous circulation (ROSC) · Part of CPCR protocol after ABCs. Vasopressin may be alternated.
- Cardiac resuscitation · 0.1-0.2 mg/kg (high dose) or 0.01-0.02 mg/kg (low dose) · IV or IO · Repeat at 3-5 minute intervals if no response · Low dose generally attempted first.
- Cardiac resuscitation · 0.01-0.02 mg/kg (IV) or 0.03-0.1 mg/kg (IT) · IV, IT · every 3-5 minutes · For IT, dilute in 5-10 mL of sterile water or normal saline.
- Neonatal resuscitation (when respiratory support/compressions fail) · 0.1-0.3 mg/kg · IV or IO
- Anaphylaxis · 0.01-0.02 mg/kg · IV, IT, IM, SC · Dosage may be doubled and given via endotracheal tube if IV line not established. Less severe cases may use IM or SC.
- Anaphylaxis · 0.2-0.5 mg (total dose) · SC or IM
投与経路
禁忌
- Narrow-angle glaucoma
- Hypersensitivity to epinephrine
- Shock due to non-anaphylactoid causes
- During general anesthesia with halogenated hydrocarbons or cyclopropane
- During labor (may delay the second stage)
- Cardiac dilatation or coronary insufficiency
- Conditions where vasopressors are contraindicated (e.g., thyrotoxicosis, diabetes, hypertension, toxemia of pregnancy)
- Injection with local anesthetics into small appendages (toes, ears, etc.) due to risk of necrosis
有害事象
- Anxiety and fear
- Tremors and excitability
- Vomiting
- Hypertension (especially with overdosage)
- Cardiac arrhythmias (especially with pre-existing heart disease)
- Hyperuricemia
- Lactic acidosis (with prolonged use or overdose)
- Tissue necrosis and sloughing at the injection site (with repeated injections or injection into small appendages)
薬物相互作用
- Alpha-blockers (phentolamine, phenoxybenzamine, prazosin) · May negate the therapeutic effects of epinephrine.
- Alpha-2 agonists (detomidine, dexmedetomidine, xylazine) · Do NOT use epinephrine to treat cardiac effects caused by alpha-2 agonists; may worsen hemodynamics.
- General Anesthetics (halogenated hydrocarbons, cyclopropane) · Increased risk of developing severe arrhythmias. Propranolol may be used to treat if they occur.
- Antihistamines (diphenhydramine, chlorpheniramine) · May potentiate the effects of epinephrine.
- Beta-blockers (propranolol) · May potentiate hypertension and antagonize epinephrine's cardiac and bronchodilating effects.
- Digoxin · Increased risk of arrhythmias if used concurrently.
- Nitrates · May reverse the pressor effects of epinephrine.
- Levothyroxine · May potentiate the effects of epinephrine.
- Oxytocic agents · Hypertension may result if used concurrently. · moderate
- Other Sympathomimetic agents (isoproterenol) · Should not be administered together as increased toxicity may result.
- Phenothiazines · May reverse the pressor effects of epinephrine.
- Reserpine · May potentiate the pressor effects of epinephrine.
モニタリング
- Cardiac rate and rhythm (ECG)
- Respiratory rate and auscultation (especially during anaphylaxis)
- Urine flow (if possible)
- Blood pressure
- Blood gases (if indicated and possible)
過量投与
Clinical signs of overdosage or inadvertent IV administration of SC/IM doses include: * Sharp rises in systolic, diastolic, and venous blood pressures * Cardiac arrhythmias * Pulmonary edema and dyspnea * Vomiting, headache, and chest pain * Cerebral hemorrhages (due to severe hypertension) * Renal failure, metabolic acidosis, and cold skin **Treatment:** Because epinephrine has a relatively short duration of effect, treatment is mainly supportive. If necessary, an alpha-adrenergic blocker (e.g., phentolamine) or a beta-adrenergic blocker (e.g., propranolol) can be used to treat severe hypertension and cardiac arrhythmias. Prolonged periods of hypotension may follow, requiring treatment with norepinephrine.
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