Dexmedetomidine

Pharmacology:

• Dexmedetomidine is an α2-adrenergic receptor agonist.

• It is the dextrorotatory enantiomer of medetomidine, about twice as potent.

• Dexmedetomidine is highly specific for α2 receptors, leading to CNS depression, analgesia, peripheral vasoconstriction, bradycardia, respiratory depression, and more.

• It has varying effects on intestinal muscle tone, blanched mucous membranes, and can cause prolonged hypertension.

Pharmacokinetics:

• In dogs (IM administration), it has 60% bioavailability, reaching peak levels in about 35 minutes.

• Volume of distribution is 0.9 L/kg, with an elimination half-life of 40-50 minutes.

• It's metabolized in the liver and eliminated primarily in urine and feces.

• In cats (IM administration), peak levels occur in about 15 minutes.

• Volume of distribution is 2.2 L/kg, with an elimination half-life of approximately 1 hour.

• Metabolites are primarily eliminated in urine and feces.

Adverse Effects:

• Adverse effects include bradycardia, vasoconstriction, muscle tremors, transient hypertension, reduced tear production, AV blocks, decreased respiration, hypothermia, urination, vomiting, hyperglycemia, and pain on IM injection.

• Rare effects may include prolonged sedation, paradoxical excitation, hypersensitivity, pulmonary edema, apnea, and circulatory failure.

Clinical Applications: 

•  Dexmedetomidine can be administered intranasally and has been effective in reducing stress in dogs.

• It is commonly used as a sole sedative or in combination with opioids for general anesthesia or improving sedation quality.

• Administering it epidurally or as a constant-rate infusion extends the duration of local regional blocks.

Contraindications/Precautions:

• Cardiovascular diseases, including valvular regurgitation or arrhythmias, are contraindications.

• Bradyarrhythmias are frequent and may require treatment with anticholinergics or lidocaine.

• Dexmedetomidine is contraindicated in patients with renal insufficiencies, anuria, or a blocked urinary system.

• Avoid use in geriatric, pregnant, pediatric, sick, or debilitated patients.

Practical Notes:

• Patients may experience transient hyperglycemia after administration.

• Provide a quiet, darkened room with minimal stimulus.

• Monitor patients and have reversal agents like atipamezole available.

• Vasoconstriction may affect mucous membrane color and pulse oximetry.

• Low doses are suitable for premedication in cats with HCM.

• Dexmedetomidine is more likely to cause vomiting in cats compared to xylazine; consider maropitant for premedication.

Dexmedetomidine Doses:

• Intranasal: A study showed that 0.02 mg/kg dexmedetomidine produced effective sedation in dogs.

• Oral transmucosal (OTM, buccal) administration in cats: Dexmedetomidine at 40 micrograms/kg appears to give similar levels as IM administration.

• Dexmedetomidine combined with buprenorphine in cats: Used at 20 micrograms/kg for IM administration.

• Dexmedetomidine combined with local anesthetic for regional anesthesia: Used at 0.001 mg/kg.

References:

• Grimm, KA. Veterinary Anesthesia and Analgesia the 5th Edition of Lumb and Jones. 2015. 

• Plumb, DC. Plumb’s Veterinary Drug Handbook. 7th edition. Pharma Vet Inc. 2011. 

• Shelby, AM. Small Animal Anesthesia Techniques. 2nd ed. Wiley Blackwell. 2023.