Veterinary Drug Handbook (VDH) is the reference veterinarians turn to when they want an independent source of information on the drugs that are used in veterinary medicine today.


Chemistry - A Rauwolfia or indolealkylamine alkaloid, yohimbine HCl has a molecular weight of390.9. It is chemically related to reserpine.

Storage, Stability, Compatibility

Yohimbine injection should be stored at room temperature(15-30°C); (Antagonil®-store in refrigerator), and protected from light and heat.

Pharmacology - YOHIMBINE HCL

Yohimbine is an alpha2-adrenergic antagonist that can antagonize the effects ofxylazine. Alone, yohimbine increases heart rate, blood pressure, causes CNS stimulation and antidiuresis, and has hyperinsulinemic effects.
By blocking central alpha2-receptors, yohimbine causes sympathetic outflow (norepinephrine) tobe enhanced. Peripheral alpha2-receptors are also found in the cardiovascular system, genitourinarysystem, GI tract, in platelets, and adipose tissue.
Uses, Indications - Yohimbine is indicated to reverse the effects of xyalzine in dogs, but it is beingused clinically in several other species as well.
Yohimbine may be efficacious in reversing some of the toxic effects associated with other agentsas well (e.g., amitraz), but additional research must be performed before additional recommendations for its use can be made.

Pharmacokinetics - YOHIMBINE HCL

The pharmacokinetics of this drug have been reported in steers, dogs, andhorses (Jernigan et al. 1988). The apparent volume of distribution (steady-state) is approximately 5
L/kg in steers, 2 - 5 L/kg in horses, and 4.5 L/kg in dogs. The total body clearance is approximately70 ml/min/kg in steers, 35 ml/min/kg in horses, and 30 ml/min/kg in dogs. The half-life of the drugis approximately 0.5 - 1 hours in steers, 0.5 - 1.5 hours in horses, and 1.5 - 2 hours in dogs.
Yohimbine is believed to penetrate the CNS quite readily and when used to reverse the effects ofxylazine, onset of action generally occurs within 3 minutes. The metabolic fate of the drug is notknown.

Contraindications, Precautions, Reproductive Safety

Yohimbine is contraindicated in patientshypersensitive to it. In humans, yohimbine is contraindicated in patients with renal disease.
Yohimbine should be used cautiously in patients with seizure disorders. When used to reverse theeffects xyalzine, normal pain perception may result.
Safe use of yohimbine in pregnant animals has not been established.

Adverse Effects, Warnings

Yohimbine may cause transient apprehension or CNS excitement, muscle tremors, salivation, increased respiratory rates, and hyperemic mucous membranes. Adverseeffects appear to be more probable in small animals than in large animals.

Overdosage, Acute Toxicity

Dogs receiving 0.55 mg/kg (5 times recommended dose) exhibitedsymptoms of transient seizures and muscle tremors.

Drug Interactions

Little information is available, use with caution with other alpha2-adrenergicantagonists or other drugs that can cause CNS stimulation. In humans, yohimbine is recommendednot to be used with antidepressants or other mood-altering agents.

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