Tolazoline
Tolazoline hydrochloride
Also known as: Tolazine ยท Priscoline ยท Vaso-Dilatan ยท benzazoline hydrochloride ยท tolazolinium chloratum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
๐ NA โ North America๐ EU โ Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| 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 | โ | ๐ NA |
- For reversal of xylazine effects: 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 dogs.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| 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 | โ | ๐ NA |
- For reversal of xylazine effects: 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.
Birds
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| As a reversal agent for alpha2-adrenergic agonists (e.g., xylazine, detomidine, etc.) | 15 mg/kg IV | IV | once | โ | ๐ NA |
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| 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 | โ | ๐ NA |
- For reversal of xylazine effects: FDA-approved for use in horses.
Cattle
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| For reversal of xylazine effects | 2-4 mg/kg slow IV ; titrate to effect | IV | once | โ | ๐ NA |
| For reversal of xylazine effects (Emergency) | 2 mg/kg IM | IM | once | โ | ๐ NA |
- For reversal of xylazine effects: Slaughter withdrawal: 30 days. Not FDA-approved in the USA for use in food animals.
- For reversal of xylazine effects (Emergency): 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.
Sheep
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| For reversal of xylazine effects | 2-4 mg/kg slow IV ; titrate to effect | IV | once | โ | ๐ NA |
| 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 | โ | ๐ NA |
- For reversal of xylazine effects: Slaughter withdrawal: 30 days. Not FDA-approved in the USA for use in food animals.
Goats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| For reversal of xylazine effects | 2-4 mg/kg slow IV ; titrate to effect | IV | once | โ | ๐ NA |
| 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 | โ | ๐ NA |
- For reversal of xylazine effects: Slaughter withdrawal: 30 days. Not FDA-approved in the USA for use in food animals.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
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 ฮฑ2-agonists like dexmedetomidine or detomidine (where atipamezole is the preferred reversal agent).
- Because it blocks both ฮฑ1 and ฮฑ2 receptors and has direct vasodilatory properties, its cardiovascular effects can be complex and sometimes unpredictable, necessitating slow and careful administration.
Mechanism of action
Tolazoline acts as a competitive antagonist at both โฮฑ1-โ and โฮฑ2-adrenergic receptorsโ.
- Central & Peripheral ฮฑ2 Blockade โ Reverses the sedation, analgesia, and bradycardia induced by ฮฑ2-agonists (like xylazine).
- Direct Smooth Muscle Relaxation โ Exerts a direct relaxant effect on vascular smooth muscle โ peripheral vasodilation โ 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.
Safety & warnings
Contraindications
- 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)
Adverse effects
- 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)
Precautions
WARNING: Rapid IV Administration Acute death and cardiac asystole have been reported after rapid IV administration of tolazoline at high dosages, particularly in camelids and cattle. Always administer IV slowly (e.g., 1 mL/second) or consider the IM route.
- High Concentration Risk: The veterinary formulation is highly concentrated (100 mg/mL), making accurate dosing difficult in small animals (dogs/cats). Yohimbine or atipamezole are generally safer alternatives for small animals.
- Human Safety: Humans with coronary artery or cerebrovascular disease should use extra caution when handling this agent.
Drug interactions
Accumulation of acetaldehyde can occur if tolazoline and alcohol are given simultaneously.
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.
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.
Monitoring
- Reversal effects (efficacy of waking up/recovery)
- Heart rate and rhythm
- Blood pressure
- Adverse effects (sweating, GI hypermotility, anxiety)
Pharmacokinetics
Half-life
Absorption
Rapid acting after IV administration (usually within 5 minutes).
Distribution
Widely distributed. Animal studies have demonstrated that tolazoline is concentrated in the liver and kidneys.
Overdose
Overdoses can cause severe cardiovascular and gastrointestinal disturbances.
- โHorses (5X overdose)โ: 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.
- โCamelids (5X overdose in a llama)โ: 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.
Available products
Formulations
- Injection: 100 mg/mL (Veterinary)
- Injection: 25 mg/mL (Human-labeled, historically)
Veterinary
- Tolazoline HCl Injection: 100 mg/mL in 100 mL multi-dose vials (Tolazineยฎ)
Regulatory status
No regulatory data for: ๐บ๐ธ US ยท ๐ช๐บ EU ยท ๐ฌ๐ง UK ยท ๐ญ๐ฐ HK ยท ๐น๐ผ TW ยท ๐ฏ๐ต JP ยท ๐ฐ๐ท KR ยท ๐ฆ๐บ AU
Storage & stability
Commercially available injection products should be stored between 15-30ยฐC and protected from light. Reportedly physically compatible with commonly used IV solutions.
Client information
Tolazoline is a medication administered exclusively by veterinary professionals to "wake up" (reverse the sedation of) your animal after a procedure or examination.
- What to Expect: As your animal wakes up, you may notice temporary side effects such as sweating, lip smacking or licking, anxiety, or muscle twitching.
- Duration: These effects are generally mild and should diminish and disappear within 2 hours of dosing.
- Safety: Because of the rapid changes in heart rate and blood pressure that can occur, your animal will be closely monitored by the veterinary team during the recovery period.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.