Pre-anesthetic medications reduce anxiety, provide analgesia, and smooth induction and recovery. They allow lower doses of induction and maintenance agents, improving cardiovascular stability. Use the Anesthesia & Analgesia Reference for dose calculations and the Anesthesiology Specialist to discuss protocols.
The most commonly used pre-meds in small animal practice include phenothiazines, alpha-2 agonists, and opioids.
Acepromazine
Acepromazine is a phenothiazine tranquilizer that provides reliable sedation and antiemetic effects. It has no analgesic properties and causes dose-dependent vasodilation, which can exacerbate hypotension in hypovolemic patients. Typical dose: 0.01-0.05 mg/kg IM or IV. Avoid in breeds predisposed to drug sensitivity (e.g., some sighthounds) and in patients with seizure history. It cannot be reversed.
Dexmedetomidine
Dexmedetomidine is a potent alpha-2 agonist providing sedation, analgesia, and muscle relaxation. It reduces MAC (minimum alveolar concentration) for inhalants by up to 50%. Side effects include bradycardia and peripheral vasoconstriction. Typical dose: 5-20 mcg/kg IM for pre-medication. It is reversible with atipamezole (0.1-0.2 mg/kg IM), making it valuable when rapid recovery is desired.
Induction agents produce rapid unconsciousness to allow endotracheal intubation. Choice depends on patient status, procedure length, and clinician preference.
| Drug | Dose (IV) | Onset | Duration | Notes |
|---|---|---|---|---|
| Propofol | 2-6 mg/kg (to effect) | 30-60 sec | 5-10 min | Smooth induction; no analgesic; can cause apnea; use in well-premedicated patients |
| Alfaxalone | 1-3 mg/kg (dogs); 2-5 mg/kg (cats) | 30-60 sec | 5-15 min | Cardiovascularly stable; good for cats; no analgesic |
| Ketamine | 5-10 mg/kg IM (combined with sedative) | 2-5 min | 20-30 min | Combination drug; use with diazepam/midazolam to prevent seizures; good analgesia |
| Etomidate | 1-2 mg/kg IV | 30-60 sec | 3-5 min | Minimal cardiovascular effects; good for critical patients; adrenal suppression |
Propofol vs Alfaxalone
Propofol is lipid-based and supports bacterial growth—use within 6-12 hours of opening. Alfaxalone is water-based and has a longer shelf life. Both provide smooth induction; alfaxalone tends to cause less apnea and is often preferred in cats. Propofol is more economical for large dogs.
Isoflurane and sevoflurane are the primary inhalants used for maintenance. Both are halogenated ethers. Sevoflurane has lower blood solubility, allowing faster induction and recovery, and is less pungent—useful for mask induction in cats. Isoflurane is more economical. Desflurane is rarely used in veterinary medicine due to equipment requirements.
When rapid recovery is needed, reversal agents can shorten recovery time. Atipamezole reverses dexmedetomidine (0.1-0.2 mg/kg IM, typically 5x the dexmedetomidine volume). Naloxone reverses opioid effects (0.01-0.02 mg/kg IV). Flumazenil reverses benzodiazepines (0.01 mg/kg IV).
Warning: Reversal can cause acute pain if analgesia was opioid-based—ensure alternative analgesia is in place.
Anesthesia should always be performed under veterinary supervision. If your pet is scheduled for a procedure, discuss the anesthetic protocol with your veterinarian. Report any previous adverse reactions, breed-specific sensitivities, or concurrent medications. Post-anesthetic complications (prolonged sedation, vomiting, inappetence, or pain) warrant a call to your vet.
- Pre-meds (acepromazine, dexmedetomidine) reduce anxiety and allow lower induction doses.
- Propofol, alfaxalone, ketamine, and etomidate are common induction agents—choice depends on patient status.
- Sevoflurane offers faster induction/recovery; isoflurane is more economical.
- Reversal agents (atipamezole, naloxone, flumazenil) shorten recovery but require alternative analgesia.
- Always discuss anesthetic protocol with your vet and report breed sensitivities or prior reactions.