Methadone
Also known as: Dolophine, Methadose, Diskets, Comfortan, Synthadon
Methadone is a potent, strictly controlled opioid analgesic. When given by injection, it is typically administered in a hospital setting under direct veterinary supervision. If you are sent home with oral methadone for your pet's pain control: * **Strictly follow the prescribed dosage.** Do not give more or less without consulting your veterinarian. * > **EXTREME DANGER:** Keep this medication in a secure location, completely out of reach of children and other pets. Accidental ingestion by a human (especially a child) can cause fatal respiratory depression. * Watch for side effects such as mild sedation, panting, whining, or constipation. * **Seek immediate veterinary care** if your pet becomes extremely lethargic, has difficulty breathing, or if their breathing becomes abnormally slow.
Dosage must be set by your veterinarian for your specific pet. Never give human medication or another pet’s prescription without veterinary guidance.
Veterinary professional? See the full dosing-by-species reference on VetSheet →
What it is used for
- For perioperative pain control
- As a pre-anesthetic
- For moderate to severe pain
- For pain
- Analgesia
- Analgesia
- Analgesia
- As an analgesic
- As a pre-anesthetic
- For pain
- For perioperative pain control
- For analgesia
- Analgesia
- Analgesia
- Epidural analgesia
How it is given
Possible side effects
- Panting
- Whining or vocalization
- Sedation
- Defecation
- Constipation
- Bradycardia
- Respiratory depression
- Pronounced CNS excitement (in horses at IV doses ≥ 0.1 mg/kg)
- Respiratory depression (primarily under general anaesthesia)
- Transient excitation (when given IV)
- Salivation (when given via oral transmucosal route in cats due to preservatives)
- Constriction of gastrointestinal sphincters (e.g., pyloric sphincter)
- Reduction in gastrointestinal motility (with prolonged use)
- Neonatal sedation (crosses the placenta)
Cautions & contraindications
- Late-term pregnancy (due to risks of respiratory depression and stillbirths)
- Known hypersensitivity to methadone
- No specific contraindications available in the monograph, but use with caution in patients with severe respiratory compromise or hepatic impairment.
- All opiates should be used with caution in patients with **heart failure**, **hypertension**, **head injuries**, **elevated CSF pressures**, and in **geriatric or severely debilitated patients**. > **Note:** Methadone can increase plasma amylase and lipase values up to 24 hours following administration due to increased biliary tract pressure.
Drug interactions
- Class I & III Antiarrhythmics (e.g., lidocaine, procainamide, quinidine, amiodarone): May increase risks for arrhythmias
- Alpha2-Agonists (e.g., medetomidine, xylazine): Potentiates sedative and analgesic effects; combination with medetomidine may cause severe hypoxemia in dogs breathing room air
- Azole Antifungals (fluconazole, itraconazole, ketoconazole): May increase methadone levels in humans (does not appear to be true for dogs)
- Calcium Channel Blockers: May increase risks for arrhythmias
- CNS Depressants (anesthetics, antihistamines, phenothiazines, barbiturates, tranquilizers): May cause increased CNS or respiratory depression
- Corticosteroids (Mineralocorticoids): May increase potential for electrolyte abnormalities
- Diuretics: Opiates may decrease diuretic efficacy in CHF patients
- Macrolide Antibiotics (erythromycin, clarithromycin): May inhibit metabolism of methadone and increase levels in humans (does not appear to be true for dogs)
- Monoamine Oxidase Inhibitors (MAOIs) (e.g., amitraz, selegiline): Potential for severe CNS/behavioral reactions; concomitant use should be avoided
- Skeletal Muscle Relaxants: Methadone may enhance neuromuscular blockade
- Phenobarbital, Phenytoin: May decrease methadone levels in humans (probably does not affect dogs)
- Rifampin: May decrease methadone levels in humans (probably does not affect dogs)
- SSRI Antidepressants (fluoxetine, sertraline): May increase methadone levels
- St. John's Wort: May decrease methadone levels in humans (probably does not affect dogs)
- Tricyclic Antidepressants (clomipramine, amitriptyline): Methadone may exacerbate the effects of tricyclic antidepressants
- Warfarin: Opiates may potentiate anticoagulant activity
- Zidovudine: Methadone may increase zidovudine levels
- CNS depressants (anaesthetics, antihistamines, barbiturates, phenothiazines, tranquillizers): Increased CNS or respiratory depression
Frequently asked questions
What is Methadone used for in pets?
Methadone is a potent, strictly controlled opioid analgesic. When given by injection, it is typically administered in a hospital setting under direct veterinary supervision. If you are sent home with oral methadone for your pet's pain control: • Strictly follow the prescribed dosage. Do not give more or less without consulting your veterinarian. • > EXTREME DANGER: Keep this medication in a secure location, completely out of reach of children and other pets. Accidental ingestion by a human (especially a child) can cause fatal respiratory depression. • Watch for side effects such as mild sedation, panting, whining, or constipation. • Seek immediate veterinary care if your pet becomes extremely lethargic, has difficulty breathing, or if their breathing becomes abnormally slow.
Is Methadone safe for my pet?
Dosage must be set by your veterinarian for your specific pet. Never give human medication or another pet’s prescription without veterinary guidance.
This article is for general education and is not a substitute for professional veterinary advice. If your pet is unwell, please consult a veterinarian.
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