トラゾリン
トラゾリンは非選択的競合的**α-アドレナリン受容体遮断薬**であり、獣医学においては主に馬や反芻動物における**キシラジン**の鎮静、鎮痛、および心血管系への作用を拮抗（リバース）するために使用されます。 * **臨床上のポイント**：キシラジンの拮抗には非常に有効ですが、デクスメデトミジンやデトミジンなどの新しい高選択性α2作動薬に対しては、特異性や効果が劣ると考えられています（これらの場合はアチパメゾールが推奨されます）。 * α1およびα2受容体の両方を遮断し、直接的な血管拡張作用を持つため、心血管系への影響が複雑で予測困難な場合があり、ゆっくりと慎重に投与する必要があります。
作用機序: Tolazoline acts as a competitive antagonist at both **α1-** and **α2-adrenergic receptors**. * **Central & Peripheral α2 Blockade** → Reverses the sedation, analgesia, and bradycardia induced by α2-agonists (like xylazine). * **Direct Smooth Muscle Relaxation** → Exerts a direct relaxant effect on vascular smooth muscle → **peripheral vasodilation** → decreases total peripheral resistance. * **Onset**: Rapid acting (usually within 5 minutes of IV administration), but has a short duration of action, meaning repeat doses may occasionally be required if re-sedation occurs.
動物種別の用量
- For reversal of xylazine effects · 2-4 mg/kg slow IV ; titrate to effect · IV · once · Slaughter withdrawal: 30 days. Not FDA-approved in the USA for use in food animals.
- For reversal of xylazine effects · 1-2 mg /kg IM. Give 50% of initial dose slow IV or IM and then determine if more is needed. · IM/IV · once
- For reversal of xylazine effects · 2-4 mg/kg slow IV ; titrate to effect · IV · once · Slaughter withdrawal: 30 days. Not FDA-approved in the USA for use in food animals.
- For reversal of xylazine effects · 1-2 mg /kg IM. Give 50% of initial dose slow IV or IM and then determine if more is needed. · IM/IV · once
- For reversal of xylazine effects · 4 mg/kg slow IV (4 mL/220 lb. of body weight); administration rate should approximate 1 mL/second · IV · once · High concentration (100 mg/mL) makes accurate dosing difficult; yohimbine or human-labeled tolazoline (25 mg/mL) may be safer alternatives. Not FDA-approved for cats.
- For reversal of xylazine effects · 2-4 mg/kg slow IV ; titrate to effect · IV · once · Slaughter withdrawal: 30 days. Not FDA-approved in the USA for use in food animals.
- For reversal of xylazine effects (Emergency) · 2 mg/kg IM · IM · once · Should not be administered IV rapidly as this can result in cardiac asystole. Effects of reversal should start to become evident about 10 minutes following IM administration.
投与経路
禁忌
- Horses exhibiting signs of stress, debilitation, or shock
- Cardiac disease or coronary artery disease
- Sympathetic blockage
- Hypovolemia
- Cerebrovascular disease
- Known hypersensitivity to the drug
- Foals (relative contraindication; adverse reactions and fatalities reported)
有害事象
- Transient tachycardia
- Peripheral vasodilation (sweating, injected mucous membranes of gingiva and conjunctiva)
- Hyperalgesia of the lips (licking, flipping of lips)
- Piloerection
- Clear lacrimal and nasal discharge
- Muscle fasciculations
- Apprehensiveness and anxiety
- Gastrointestinal hypermotility (flatulence, diarrhea, mild colic)
薬物相互作用
- Alcohol · Accumulation of acetaldehyde can occur if tolazoline and alcohol are given simultaneously.
- Epinephrine · If large doses of tolazoline are given with epinephrine, a paradoxical drop in blood pressure can occur followed by a precipitous increase in blood pressure.
- Norepinephrine · If large doses of tolazoline are given with norepinephrine, a paradoxical drop in blood pressure can occur followed by a precipitous increase in blood pressure.
モニタリング
- Reversal effects (efficacy of waking up/recovery)
- Heart rate and rhythm
- Blood pressure
- Adverse effects (sweating, GI hypermotility, anxiety)
過量投与
Overdoses can cause severe cardiovascular and gastrointestinal disturbances. * **Horses (5X overdose)**: Gastrointestinal hypermotility resulting in flatulence, defecation, mild colic, and transient diarrhea. Intraventricular conduction may be slowed (prolongation of the QRS-complex). Ventricular arrhythmias and death may occur at higher overdoses. * **Camelids (5X overdose in a llama)**: Anxiety, hyperesthesia, profuse salivation, GI tract hypermotility, diarrhea, convulsions, hypotension, and tachypnea. Successfully treated with IV diazepam, phenylephrine, IV fluids, and oxygen. * **Human Treatment Note**: Ephedrine (NOT epinephrine or norepinephrine) has been recommended to treat serious tolazoline-induced hypotension.
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