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One selection filters the source overview, clinical facts, reports and dose calculator. Literature references are not species-filtered.
Choose one species for its overview and dose calculator, or all species to browse the full evidence.
Source overview
Recorded excerpts for one species. Each dose remains a separate source entry; no regimen is selected.
Choose one species to view its source overview. All-species evidence remains available below.
View full clinical evidence and sources ↓Clinical evidence
Pending clinical review (PROPOSED)Rule-based (RULE_BASED)— applies to the facts and dose entries in this species selection; individual source records retain their own status.
Indications2
Analgesia, sedation, anesthetic adjunct
DogCatExtra-label (EXTRA_LABEL)2 source records · View provenance
- Dog · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Indications table · Not applicable · Extra-label (EXTRA_LABEL) · Pending clinical review (PROPOSED) · Rule-based
Original excerpt: Analgesia, sedation, anesthetic adjunct — Extra-label (US); licensed formulation exists in Europe
- Cat · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Indications table · Not applicable · Extra-label (EXTRA_LABEL) · Pending clinical review (PROPOSED) · Rule-based
Original excerpt: Analgesia, sedation, anesthetic adjunct — Extra-label (US); licensed formulation exists in Europe
- Dog · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Indications table · Not applicable · Extra-label (EXTRA_LABEL) · Pending clinical review (PROPOSED) · Rule-based
Dose regimens4
This calculator performs arithmetic only on the sourced dosing field shown for each result — it does not verify the field's accuracy, does not select which field to use for a patient, and does not replace a veterinarian's order. Not for clinical use. Confirm every result against the primary source before dispensing.
Choose one species above to view its dose calculator.
Adverse effects203
Panting, sedation, defecation, constipation, bradycardia — Common, generally milder than morphine
DogNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Dog · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Side Effects / Adverse Effects table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Less excitation/vomiting than other mu-agonists — Comparatively favorable profile
CatNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Cat · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Side Effects / Adverse Effects table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
CNS excitement at IV ≥0.1 mg/kg — Dose-related
HorseNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Horse · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Side Effects / Adverse Effects table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
These are counts of spontaneously reported events, not proven adverse effects, causal relationships, or incidence rates.
Bars compare report counts within each species; they do not show incidence.
More reportsFewer reportsDog
- Lethargy (see also Central nervous system depression in Neurological)48 reports
- Death by euthanasia37 reports
- Diarrhoea37 reports
- Not eating35 reports
- Vomiting34 reports
- Elevated serum alkaline phosphatase (ALP)28 reports
- Fever26 reports
- Hypotension26 reports
- Tachycardia25 reports
- Decreased appetite24 reports
- Lack of efficacy - NOS24 reports
- Pain NOS24 reports
Cat
- Death17 reports
- Not eating17 reports
- Behavioural disorder NOS14 reports
- Hyperactivity11 reports
- Lethargy (see also Central nervous system depression in Neurological)10 reports
- Bradycardia9 reports
- Cardiac arrest9 reports
- Anorexia8 reports
- Dehydration8 reports
- Dilated pupils8 reports
- Hyperglycaemia8 reports
- Hypotension7 reports
Monitoring1
Analgesic/preanesthetic efficacy; respiratory status at higher doses
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Monitoring Parameters · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Contraindications1
Hypersensitivity
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Contraindications & Warnings table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Precautions3
Heart failure, hypertension, head injury/↑ICP, geriatric/debilitated patients
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Contraindications & Warnings table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Causes less histamine release, sedation, and vomiting than morphine — often preferred where available.
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Clinical pearl · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Oral bioavailability in dogs is too poor for oral dosing; buccal route is a cat-specific option, not a dog one.
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Clinical pearl · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Interactions6
Chloramphenicol — ↓ clearance, ↑ methadone plasma levels (documented in dogs)
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Drug Interactions table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Alpha-2 agonists (medetomidine, xylazine) — Potentiates sedation/analgesia — watch for hypoxemia in room-air-breathing patients
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Drug Interactions table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
MAO inhibitors (amitraz, selegiline) — Avoid — risk of severe CNS/behavior reaction (extrapolated from meperidine data)
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Drug Interactions table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Azole antifungals, macrolides — May increase methadone levels in other species (not clearly demonstrated in dogs)
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Drug Interactions table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
SSRIs — May increase methadone levels
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Drug Interactions table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Pharmacokinetics4
Potency — ~1–1.5x morphine, more lipid-soluble
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Pharmacokinetics table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Half-life — 1.75–4h IV (dog); ~11h after SC (wide variability); ~1–2h (horse)
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Pharmacokinetics table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Metabolism — Hepatic; CYP3A not a major pathway in dogs (unlike humans)
DogNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Dog · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Pharmacokinetics table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Elimination — Renal/hepatic (human data extrapolated)
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Pharmacokinetics table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Pregnancy / lactation considerations1
Relatively safe at low doses in first two trimesters (human data); avoid late-term — respiratory depression/stillbirth risk reported in humans. Compatible with breastfeeding per AAP (human guidance).
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 794–796; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 501–503 — Pregnancy & Lactation · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Literature references9
References are linked to this drug. Species applicability is not recorded here, so the species filter does not narrow this list. Imported dates do not retain their original precision; confirm dates in the original citation.
- Use of epidural anaesthesia as analgesic management in an asiatic lion (Panthera leo persica).
Study summary not available in the imported record. Open the original citation to review the study.
- Keeping an eye on pain: Characterization of pain behaviours in cats undergoing ophthalmic surgery.
Study summary not available in the imported record. Open the original citation to review the study.
- Evaluation of cardiac effects of a medetomidine-vatinoxan and methadone combination in healthy dogs: radiographic and echocardiographic assessment.
Study summary not available in the imported record. Open the original citation to review the study.
- Linalool, linalyl acetate, and lavender essential oil: evaluation of metabolism and drug interactions using canine liver microsomes and recombinant enzymes.
Study summary not available in the imported record. Open the original citation to review the study.
- Lignocaine and phenylephrine spray prior to brachycephalic obstructive airway syndrome surgery in dogs reduces postoperative regurgitation: a prospective, randomized, controlled trial.
Study summary not available in the imported record. Open the original citation to review the study.
Sources: PubMed, National Library of Medicine; openFDA, U.S. Food and Drug Administration; Plumb DC. Plumb's Veterinary Drug Handbook. 7th ed. PharmaVet Inc; 2011.
Owner information handout
Plain-language medication information to review with the owner. Open the handout to print it or download a PDF.
Available products
Products listed in the Health Canada Drug Product Database for this active ingredient. A listing does not establish that a product is authorized for the clinical uses described on this page.