ドパミン
ドパミンは内因性の**カテコールアミン**であり、ノルアドレナリンの直接の代謝前駆体です。獣医療の集中治療において、主に適切な輸液蘇生を*行った後*の血行動態の不安定性（特に低血圧性ショックや急性心不全）を管理するため、持続静脈内投与（CRI）として使用されます。 ### 臨床上のハイライト * **用量依存性の効果**: ドパミンの受容体親和性は輸注速度によって劇的に変化し、ドパミン作動性（血管拡張）からβ1（強心作用）、そしてα1（昇圧作用）へと移行します。 * **腎用量に関する議論**: 歴史的に、「低用量」ドパミンは乏尿性急性腎障害における利尿を促進するために使用されてきました。しかし現代のエビデンスでは、糸球体濾過量（GFR）を有意に改善しないことが示されており、犬での使用は証明されていないか議論の余地があり、猫では有害となる可能性があります。 * **厳格な投与規則**: 専用の静脈ラインとシリンジポンプまたは輸液ポンプを使用して投与する必要があります。**血管外漏出**は重篤な組織壊死を引き起こします。
作用機序: Dopamine acts directly on **dopaminergic**, **β1-adrenergic**, and **α1-adrenergic** receptors, and indirectly by stimulating the release of endogenous norepinephrine from sympathetic nerve terminals. Its effects are highly dose-dependent: * **Low Dose (0.5–2 µg/kg/min)**: Primarily stimulates **D1 and D2 dopaminergic receptors** → vasodilation of renal, mesenteric, coronary, and intracerebral vascular beds. Increases renal blood flow and urine output, but does not appreciably increase GFR. * **Medium Dose (2–10 µg/kg/min)**: Stimulates **β1-adrenergic receptors** in the myocardium → increases intracellular cAMP → positive inotropic (increased contractility) and mild chronotropic (increased heart rate) effects. Improves cardiac output and organ perfusion. * **High Dose (>10–12 µg/kg/min)**: Overrides dopaminergic effects and strongly stimulates **α1-adrenergic receptors** in the vasculature → profound vasoconstriction → increases systemic vascular resistance (SVR) and blood pressure. Renal and peripheral blood flows are decreased at these rates.
動物種別の用量
- Vasodilatory shock if fluid resuscitation and dobutamine is not successful · 2.5-10 micrograms/kg/min · IV · CRI · Titrated to effect · If not successful may try adding norepinephrine.
- Treatment of severe hypotension/shock · 1-3 micrograms/kg/minute CRI; higher dosages of 3-10 micrograms/kg/min CRI are indicated if greater cardiotonic and BP support are indicated · IV · CRI · Titrated to effect · Not a substitute for adequate volume replacement therapy.
- Treatment of severe hypotension/shock after fluid correction and if dobutamine does not give desired effect · 1-10 micrograms/kg/min · IV · CRI · Titrated to effect
- Vasodilatory shock if fluid resuscitation and dobutamine is not successful · 2.5-10 micrograms/kg/min · IV · CRI · Titrated to effect · If not successful may try adding norepinephrine.
- Adjunctive therapy for acute heart failure · 1-10 micrograms/kg/min · IV · CRI · Titrated to effect · Initially, a dose of 2 micrograms/kg/min is usually used and titrated upward to desired clinical effect. Doses higher than 10 may increase peripheral vascular resistance and heart rate.
- Treatment of severe hypotension/shock · 1-3 micrograms/kg/minute CRI; higher dosages of 3-10 micrograms/kg/min CRI are indicated if greater cardiotonic and BP support are indicated · IV · CRI · Titrated to effect · Not a substitute for adequate volume replacement therapy.
- Treatment of severe hypotension/shock after fluid correction and if dobutamine does not give desired effect · 1-10 micrograms/kg/min · IV · CRI · Titrated to effect
投与経路
禁忌
- Pheochromocytoma
- Ventricular fibrillation
- Uncorrected tachyarrhythmias
- Uncorrected hypovolemia (must replace fluids first)
有害事象
- Nausea and vomiting
- Ectopic beats (arrhythmias)
- Tachycardia
- Palpitations
- Hypotension (at low doses) or Hypertension (at high doses)
- Dyspnea
- Vasoconstriction (reduced peripheral circulation)
- Severe tissue necrosis and sloughing (if extravasated)
薬物相互作用
- Alpha-adrenergic blockers (e.g., prazosin) · May antagonize the vasoconstrictive properties of high-dose dopamine.
- Halogenated hydrocarbon anesthetics (e.g., halothane) · May result in increased incidences of ventricular arrhythmias.
- Tricyclic antidepressants · May potentiate adverse cardiovascular effects.
- Beta-blockers (e.g., propranolol, metoprolol) · May antagonize the cardiac (inotropic/chronotropic) effects of dopamine.
- Diuretics · May potentiate urine production effects of low-dose dopamine.
- Monoamine oxidase inhibitors (MAOIs) · Can significantly prolong and enhance the effects of dopamine.
- Oxytocic drugs · May cause severe hypertension when used concurrently.
- Phenothiazines · May antagonize the renal and mesenteric vasodilatation effects of dopamine.
- Vasopressors/Vasoconstrictors · Concurrent use may cause severe hypertension.
モニタリング
- Continuous electrocardiogram (ECG) for cardiac rate and rhythm
- Direct or indirect blood pressure
- Urine output/flow
- IV catheter site (frequent checks for patency and signs of extravasation)
過量投与
Accidental overdosage is primarily manifested by **excessive blood pressure elevation** (severe hypertension) and arrhythmias. * **Treatment**: Because dopamine's half-life is extremely short (~2 minutes), treatment usually consists only of temporarily discontinuing the IV infusion or reducing the rate until parameters normalize. * If the patient's condition fails to stabilize rapidly after discontinuation, the alpha-adrenergic antagonist **phentolamine** may be administered.
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