Tolazoline
Tolazoline is a non-selective, competitive **alpha-adrenergic antagonist** primarily utilized in veterinary medicine to reverse the sedative, analgesic, and cardiovascular effects of **xylazine**, particularly in equine and ruminant practice. * **Clinical Pearl**: While highly effective for reversing xylazine, tolazoline is generally considered less specific and less effective for newer, highly selective α2-agonists like dexmedetomidine or detomidine (where atipamezole is the preferred reversal agent). * Because it blocks both α1 and α2 receptors and has direct vasodilatory properties, its cardiovascular effects can be complex and sometimes unpredictable, necessitating slow and careful administration.
Mecanismo: 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.
Dosificación por especie
- 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.
Vías de administración
Contraindicaciones
- 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)
Efectos adversos
- 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)
Interacciones farmacológicas
- 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.
Monitoreo
- Reversal effects (efficacy of waking up/recovery)
- Heart rate and rhythm
- Blood pressure
- Adverse effects (sweating, GI hypermotility, anxiety)
Sobredosis
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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