Yohimbine
Yohimbine is an indolealkylamine alkaloid and a specific **alpha-2 adrenergic antagonist**. It is primarily utilized in veterinary medicine to reverse the sedative and cardiovascular effects of alpha-2 agonists, particularly **xylazine**. Beyond anesthetic reversal, yohimbine is highly effective as an antidote for **amitraz toxicity** (often seen with tick dips or collars) and can even be used prophylactically before amitraz administration. While its use for reversing modern alpha-2 agonists like dexmedetomidine has largely been supplanted by atipamezole, yohimbine remains a valuable emergency and reversal agent. It has also been investigated for use as an antiemetic in specific clinical scenarios.
Mechanism: Yohimbine competitively blocks central and peripheral **presynaptic alpha-2 adrenergic receptors**. - **Mechanism:** By blocking these autoreceptors, yohimbine prevents the negative feedback loop that normally inhibits neurotransmitter release โ **increases synaptic norepinephrine** release โ enhances sympathetic outflow. - **Systemic Effects:** This surge in sympathetic tone results in increased heart rate, elevated blood pressure, CNS stimulation, and antidiuresis, effectively counteracting the profound sedation, bradycardia, and hypotension induced by alpha-2 agonists.
Dosing by species
- Xylazine reversal (Llamas/Camelids) ยท 0.25 mg/kg IV or IM ยท IV/IM ยท once ยท Dosing specifically reported for Llamas.
- Xylazine reversal ยท 0.125 mg/kg IV ยท IV ยท once
- Xylazine reversal (Routine/Emergency) ยท IM administration preferred for routine; 0.1 mg/kg IV for emergency ยท IM/IV ยท once ยท IM preferred to decrease CNS/CV risks. Wait 30-45 min post-IM or 15-30 min post-IV xylazine to allow ketamine/Telazol to resolve before reversing.
- Xylazine reversal ยท 0.075 mg/kg IV ยท IV ยท once ยท ARCI UCGFS Class 2 Drug.
- Alpha2-adrenergic agonist reversal (e.g., xylazine) ยท 0.1 mg/kg IV ยท IV ยท once
- Xylazine reversal (Rabbits) ยท 0.2 mg/kg IV ยท IV ยท as needed ยท Also partially antagonizes ketamine and acepromazine.
- Xylazine reversal (Mice/Rats) ยท 0.2 mg/kg IP ยท IP ยท as needed ยท Also partially antagonizes ketamine and acepromazine.
Routes of administration
Contraindications
- Hypersensitivity to yohimbine
- Renal disease (extrapolated from human medicine)
- Patients with active seizure disorders
Adverse effects
- Transient apprehension or anxiety
- CNS excitement
- Muscle tremors
- Hypersalivation
- Increased respiratory rate (panting)
- Hyperemic (red) mucous membranes
- Tachycardia
Drug interactions
- Tricyclic Antidepressants ยท May cause severe hypertension; concurrent use is not recommended.
- Other Alpha-2 Antagonists ยท Additive antagonistic effects; use with caution.
- CNS Stimulants ยท Additive CNS stimulation and increased risk of seizures or severe agitation.
Monitoring
- CNS status (arousal level, signs of excitement or apprehension)
- Cardiac rate and rhythm
- Blood pressure (if indicated and practical)
- Respiratory rate and effort
Overdose
Overdoses can cause significant CNS and cardiovascular overstimulation. - **Experimental Data:** Dogs receiving 0.55 mg/kg (5 times the recommended dose) exhibited clinical signs of transient seizures and muscle tremors. - **Clinical Reports (APCC):** Reported findings in dogs include diarrhea, disorientation, hyperactivity, panting, tachycardia, and hypersalivation. - **Treatment:** Primarily supportive and symptomatic. Avoid further CNS stimulation and manage seizures if they occur.
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.