Oxymorphone, a Schedule II semi-synthetic opiate derived from thebaine, possesses a structure similar to that of morphine, which makes it part of phenanthrenes group1. Additionally, this drug is a µ receptor agonist and is 5-10 times more potent than morphine1,2. It is prescribed as a narcotic analgesic for moderate to moderately severe pain under the following trade name: Opana. Prescriptions for oxymorphone have increased from approximately 268,000 in 2007 to 1.22 million in 20123.
Oxymorphone is administered orally in tablet form with typical doses of 5-10 mg or as an extended release with a dose of 5-40 mg. Additionally, it may be administered as a 1 mg/mL solution for parenteral injection5.
Following a 5-20 mg oral dose of oxymorphone, peak plasma concentrations occurred around 0.5 hours with a half-life of 4-12 hours5.
Oxymorphone is extensively metabolized via glucuronidation and reduction, with greater than 95% of the dose metabolized to form conjugated oxymorphone along with minor amounts of 6-oxymorphol5.
Approximately 1.9% of parent drug, 44% of conjugated hydromorphone, and traces of minor metabolites are excreted in the 120 hour urine5.
For qualitative analysis, oxymorphone demonstrates poor cross-reactivity with the opiate assay; therefore, the highly specific oxycodone screening Enzyme Immunoassay (EIA) methodology is utilized with an approximately equivalent cutoff concentration of 300 ng/mL6. Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS/MS) is used to confirm and quantify oxymorphone, with a cutoff concentration of 20 ng/mL. The urine samples are hydrolyzed prior to analysis and the total oxymorphone concentration is reported.
The interpretation of patients prescribed oxymorphone should be conducted with caution since it is a prescription drug and a metabolite of oxycodone. Patients prescribed oxymorphone should not have oxycodone present in their urine. However, oxymorphone preparations may contain hydromorphone and oxycodone as an impurity up to 0.1% and 0.4%, respectively7.