プロカインおよびアドレナリン
プロカインは短時間作用型のエステル型局所麻酔薬です。アドレナリンは血管収縮薬として添加され、作用時間を延長し全身への吸収速度を低下させることで、全身毒性のリスクを軽減します。 **臨床のポイント：** プロカインは血漿中の偽コリンエステラーゼによって急速に加水分解されるため比較的安全ですが、アドレナリンを添加しないと作用時間は非常に短くなります。主に局所浸潤麻酔や神経ブロックに使用されます。
作用機序: Procaine causes a reversible blockade of the **voltage-gated sodium channels** → prevents the influx of sodium → inhibits the propagation of action potentials along the nerve fiber. Sensory nerve fibers are blocked before motor nerve fibers, allowing a selective sensory blockade at low doses. Epinephrine stimulates **alpha-1 adrenergic receptors** → local vasoconstriction → delays systemic absorption of procaine, increasing its local duration of action.
投与経路
禁忌
- Intravenous administration
- Use in areas supplied by end-arteries (e.g., tail, ears, digits) due to risk of ischemic necrosis
- Known hypersensitivity to ester-type local anesthetics or PABA
- Epidural use (depending on specific formulation preservatives)
有害事象
- Local tissue irritation
- Ischemia or tissue necrosis (due to epinephrine)
- CNS excitation followed by depression (at toxic doses)
- Cardiovascular depression, hypotension, or arrhythmias (at toxic doses)
- Allergic reactions (ester anesthetics are metabolized to PABA, a known allergen)
薬物相互作用
- Sulfonamide antibiotics · Procaine is metabolized to PABA, which competitively antagonizes the antibacterial effect of sulfonamides. · major
- Alpha-adrenergic blockers · May antagonize the vasoconstrictive effects of epinephrine. · moderate
- Halothane · Sensitizes the myocardium to catecholamines; increased risk of arrhythmias with epinephrine. · major
モニタリング
- Heart rate and rhythm
- Blood pressure
- Signs of CNS toxicity (tremors, seizures)
- Tissue perfusion at the injection site
過量投与
Overdose or accidental IV injection can lead to systemic toxicity. * **CNS signs:** Restlessness, tremors, seizures, followed by severe CNS depression. * **Cardiovascular signs:** Arrhythmias, hypotension, and cardiovascular collapse. * **Treatment:** Supportive care, oxygen therapy, control seizures with diazepam or midazolam, and manage arrhythmias. Intravenous lipid emulsion (ILE) therapy may be considered for severe local anesthetic systemic toxicity (LAST).
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