Oxymorphone

Oxymorphone HCl

Opiate AgonistIVIMSCEpiduralRectalPODogsCatsSmall MammalsFerretsHorsesSwine

Also known as: Numorphan · Opana · 7,8-Dihydro-14hydroxymorphinone hydrochloride · oximorphone hydrochloride

Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference

Up to 0.2 mg/kg IM or IV ; initially a maximum of 5 mg total doseIM/IV· Once

Body weight— 🐕

Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.

Dosing by species

🌎 NA — North America🌍 EU — Europe

Dogs

Indication	Dose	Route	Frequency	Duration	Region
For sedation for minor procedures	Up to 0.2 mg/kg IM or IV ; initially a maximum of 5 mg total dose	IM/IV	Once	—	🌎 NA
For sedation for minor procedures	0.05-0.1 mg/kg IV or 0.1-0.2 mg/kg IM, SC	IV/IM/SC	Once	—	🌎 NA
For analgesia (acute pain)	0.1-0.2 mg/kg IM, IV, or SC	IM/IV/SC	q1-3h	—	🌎 NA
For analgesia (acute pain) in animals with cardiovascular disease	0.05-0.1 mg/kg IV, IM or SC	IV/IM/SC	q2-4h	—	🌎 NA
Epidural administration	0.05 mg/kg	Epidural	Once	—	🌎 NA
For acute pain	0.1-0.2 mg/kg IM or SC	IM/SC	q3-4h	—	🌎 NA
For analgesia	0.05-0.4 mg/kg IV, IM, or SC	IV/IM/SC	q2-4h	—	🌎 NA
For premedication to anesthesia in healthy dogs	0.05-0.1 mg/kg IM, IV ; 0.2 mg/kg for extra heavy sedation	IM/IV	Once	—	🌎 NA

For sedation for minor procedures: Combine with acepromazine 0.05-0.1 mg/kg IM or IV
Epidural administration: Recommend to dilute with sterile saline to a volume not to exceed 0.3 mL/kg to a maximum of 6 mL. Use of preservative-free opioids is best.
For premedication to anesthesia in healthy dogs: Maximum initial dose: 5 mg.

Cats

Indication	Dose	Route	Frequency	Duration	Region
As a preanesthetic/analgesic	0.05-0.1 mg/kg IM	IM	Once	—	🌎 NA
As an analgesic (acute pain)	0.05-0.1 mg/kg IM, SC or IV	IM/SC/IV	q1-3h	—	🌎 NA
As an analgesic (acute pain) for animals with cardiovascular disease	0.05-0.1 mg/kg IV, IM or SC	IV/IM/SC	q2-4h	—	🌎 NA
As an analgesic (acute pain)	0.025-0.1 mg/kg IV (IM or SC)	IV/IM/SC	q2-6h	—	🌎 NA
As an analgesic (acute pain)	0.02-0.1 mg/kg IV, IM, or SC	IV/IM/SC	q3-4h	—	🌎 NA

As a preanesthetic/analgesic: may cause dysphoria or excitement, add sedative.
As an analgesic (acute pain): concomitant tranquilization recommended

Small Mammals

Indication	Dose	Route	Frequency	Duration	Region
Analgesia	0.2 mg/kg IM	IM	q2-4h	—	🌎 NA
Anesthetic/analgesic for minor surgical procedures	0.15 mg/kg IM	IM	Once	—	🌎 NA
Analgesia	0.2-0.5 mg/kg SC, IM	SC/IM	q6-12h	—	🌎 NA
Analgesia	0.05-0.2 mg/kg SQ (or IM for rabbits only)	SQ/IM	q8-12 hrs	—	🌎 NA

Analgesia: Rabbits
Anesthetic/analgesic for minor surgical procedures: for a hamster-sized animal
Analgesia: Hamsters, Gerbils, Mice, Rats, Guinea pigs
Analgesia: Rabbits, Rats, Mice, Gerbils, Guinea Pigs, Hamsters, Chinchillas

Ferrets

Indication	Dose	Route	Frequency	Duration	Region
Analgesia	0.05-0.2 mg/kg IV or IM	IV/IM	2-4 times daily	—	🌎 NA
Analgesia	0.05-0.2 mg/kg SQ or IM	SQ/IM	q8-12 hrs	—	🌎 NA

Horses

Indication	Dose	Route	Frequency	Duration	Region
As an analgesic	0.01-0.02 mg/kg IV	IV	Once	—	🌎 NA
As an analgesic	0.01-0.022 mg/kg IV ; up to 15 mg total	IV	Once	—	🌎 NA
As an analgesic	0.02-0.03 mg/kg IM	IM	Once	—	🌎 NA
As an analgesic	0.015-0.03 mg/kg IV	IV	Once	—	🌎 NA
Anesthetic induction in severely compromised horses	0.01-0.022 mg/kg IV	IV	Once	—	🌎 NA

As an analgesic: divide dose into 3-4 increments and give several minutes apart
Anesthetic induction in severely compromised horses: after approx. 45 minutes, may be necessary to 'top off' with another 1/3 of the original dose

Swine

Indication	Dose	Route	Frequency	Duration	Region
To increase analgesia when used with ketamine/xylazine	0.075 mg/kg IV	IV	Once	—	🌎 NA

To increase analgesia when used with ketamine/xylazine: duration of anesthesia and recumbency: 20-30 minutes

Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.

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Overview

Oxymorphone is a potent, semi-synthetic opiate agonist used primarily as a sedative/restraining agent, analgesic, and preanesthetic in veterinary medicine.

Potency: It is approximately 10 times more potent than morphine on a per-weight basis.
Cardiovascular Effects: Its effects on the cardiovascular system are usually not clinically significant, making it a relatively safe choice for patients with cardiovascular disease.
Histamine Release: Unlike morphine or meperidine, oxymorphone does not appear to cause significant histamine release when administered intravenously.
Clinical Pearl: It is a Schedule II (C-II) controlled substance due to its high potential for abuse. While highly effective for moderate to severe pain, availability and expense can sometimes be limiting factors in veterinary practice.

Mechanism of action

Oxymorphone acts primarily as a full agonist at mu (μ) opioid receptors, with some possible activity at delta (δ) receptors.

Pathway: Binds to G-protein coupled mu-opioid receptors in the CNS (limbic system, spinal cord, thalamus, midbrain) and peripheral tissues (GI tract, urinary tract) → inhibits adenylate cyclase → decreases intracellular cAMP → promotes opening of potassium channels and inhibits voltage-gated calcium channels → hyperpolarizes nociceptive neurons and inhibits the release of pain neurotransmitters (e.g., Substance P).
Effects: This results in profound analgesia, sedation, respiratory depression, and altered GI motility.

Safety & warnings

Contraindications

Hypersensitivity to narcotic analgesics
Patients receiving monoamine oxidase inhibitors (MAOIs)
Diarrhea caused by a toxic ingestion (until toxin is eliminated)
Scorpion stings (Centruroides sculpturatus and C. gertschi)

Adverse effects

Respiratory depression
Bradycardia
Decreased GI motility (constipation)
Panting (commonly seen in dogs)
Ataxia, hyperesthesia, and behavioral changes (cats at high dosages)
CNS excitement (horses)

Precautions

Extreme Caution: Use with extreme caution in patients with head injuries, increased intracranial pressure, acute abdominal conditions (e.g., colic, as it may obscure diagnosis), respiratory disease, or acute respiratory dysfunction.

Caution: Use cautiously in patients with hypothyroidism, severe renal insufficiency, adrenocortical insufficiency, preexisting bradyarrhythmias, and in geriatric or severely debilitated patients.
Species Specifics: In cats, high dosages can produce bizarre behavioral changes; concomitant use of a tranquilizer is recommended. In horses, opiates can mask behavioral and cardiovascular signs of mild colic.

Drug interactions

Butorphanol, Buprenorphine, Nalbuphine

Potentially could antagonize opiate effects

CNS Depressants

Additive CNS effects possible

Diuretics

Opiates may decrease efficacy in CHF patients

Monoamine Oxidase Inhibitors (MAOIs)

Extreme caution; may cause signs of opiate overdose

Muscle Relaxants, Skeletal

Oxymorphone may enhance effects

Phenothiazines

May antagonize analgesic effects and increase risk for hypotension

Tricyclic Antidepressants

Oxymorphone may exacerbate the effects of tricyclic antidepressants

Warfarin

Opiates may potentiate anticoagulant activity

Monitoring

Respiratory rate/depth
CNS level of depression/excitation
Blood pressure (especially with IV use)
Analgesic activity
Cardiac rate

Pharmacokinetics

Half-life

CatsProlonged due to deficient glucuronidation

Absorption

Absorbed when given by IV, IM, SC, and rectal routes. Oral bioavailability is reduced due to a high first-pass effect. Analgesic efficacy usually occurs within 3-5 minutes after IV administration, and about 15 minutes after IM administration.

Distribution

Concentrates in the kidney, liver, and lungs; lower levels are found in the CNS. Crosses the placenta and is distributed into maternal milk.

Metabolism

Metabolized in the liver primarily by glucuronidation. Cats are deficient in this metabolic pathway, leading to prolonged half-lives.

Elimination

The kidneys excrete the glucuronidated metabolite.

Overdose

Massive overdoses may produce profound respiratory and/or CNS depression in most species. Other effects may include cardiovascular collapse, hypothermia, and skeletal muscle hypotonia.

Antidote: Naloxone is the agent of choice in treating respiratory depression.
Management: In massive overdoses, naloxone doses may need to be repeated. Animals should be closely observed as naloxone's effects sometimes diminish before sub-toxic levels of oxymorphone are attained. Mechanical respiratory support should be considered in cases of severe respiratory depression.

Available products

Formulations

Injection
Extended-Release Oral Tablets
Suppositories

Human-labeled

Oxymorphone HCl Oral Tablets: 5 mg & 10 mg; Opana®
Oxymorphone HCl Extended-Release Oral Tablets: 5 mg, 7.5 mg, 10 mg, 15 mg, 20 mg, 30 mg & 40 mg; Opana® ER
Oxymorphone HCl for Injection: 1 mg/mL in 1 mL amps; Opana®

Regulatory status

No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU

Storage & stability

The injection should be stored protected from light and at room temperature (15-30°C); avoid freezing. Commercially available suppositories should be stored at temperatures between 2-15°C.

Client information

When given parenterally, this agent should be used in an inpatient setting or with direct professional supervision.
Safety Warning: This is a potent opioid and a controlled substance. If dispensed for home use, keep strictly out of reach of children and other pets.

VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.