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Oxymorphone Hydrochloride (Numorphan®)

By: Dr. Nicholas Dodman

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  • Oxymorphone hydrochloride is a painkilling drug chemically similar to morphine, but 10 times more powerful.
  • Like morphine, oxymorphone can produce dependence, and sudden withdrawal may result in a withdrawal syndrome.
  • The body contains various opiate receptors involved in pain detection and regulation. Oxymorphone acts on certain ("opioid") receptors, primarily mu receptors, resulting in analgesia (pain relief).
  • Oxymorphone affects various body functions. Dogs and cats may vomit after administration. However, oxymorphone typically produces less vomiting than morphine.
  • Pharmacological difference between oxymorphone and morphine include the fact that oxymorphone does not release histamine, is a weaker cough suppressant, and may produce less vomiting.
  • Oxymorphone is a prescription drug. It is classified as a schedule II controlled substance.
  • This drug is not approved for use in animals by the Food and Drug Administration (FDA) but may be prescribed legally by veterinarians as an extra-label drug.

    Brand Names and Other Names

  • This drug is registered for use in humans only.
  • Human formulations: Numorphan® (Endo Labs)
  • Veterinary formulations: None

    Uses of Oxymorphone

  • Oxymorphone is used in the management of moderate to severe pain and for chemical restraint. It is often used in combination with a neuroleptic drug.
  • Oxymorphone is also used as a premedicant and as an anesthetic induction agent.

    Precautions and Side Effects

  • While generally safe and effective when prescribed by a veterinarian, oxymorphone may cause side effects in some animals.
  • Oxymorphone should not be used in animals with known hypersensitivity or allergy to the drug.
  • It should be used with care in patients prone to, or exhibiting, heart rhythm disorders.
  • Oxymorphone should be used with caution in patients with reduced thyroid function, kidney disorders, hormonal disorders, and in elderly or weakened patients.
  • It should also be used with caution in patients with head injuries.
  • Side effects include depressed breathing, so this drug should be used with caution in patients with respiratory conditions.
  • Oxymorphone interacts with some other medications. Consult your veterinarian to determine if medications your pet is receiving could interact with morphone. Such drugs include central nervous system depressants and monoamine oxidase inhibitors.
  • Oxymorphone can cause vomiting.

    How Oxymorphone is Supplied

  • The injectable form is available in a concentration of 1.0 or 1.5 mg/mL oxymorphone.
  • The suppository form contains 5 mg of oxymorphone.

    Dosing Information

  • Medication should never be administered without first consulting your veterinarian.
  • Oxymorphine is typically only used in a hospital setting.
  • In dogs, oxymorphone is dosed at 0.025 to 0.1 mg per pound (0.05 to 0.2 mg/kg) intravenously, subcutaneously, or intramuscularly.
  • The maximum dose is 3 mg per dog.
  • The epidural dose of oxymorphone in dogs is 0.025 mg per pound (0.05 mg/kg).
  • In cats, oxymorphone is dosed at 0.0125 to 0.025 mg per pound (0.025 to 0.05 mg/kg) intravenously, subcutaneously, or intramuscularly.

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