Oxycodone and oxymorphone are both powerful medications used to manage pain, and while their names sound similar, they are distinct opioid drugs. Both are prescribed for their strong analgesic properties, yet they have differences in their chemical makeup and how they are used in medical practice.
Defining Oxycodone and Oxymorphone
Oxycodone is a semi-synthetic opioid analgesic, meaning it is derived from natural opium alkaloids but modified in a laboratory. It is commonly prescribed for the relief of moderate to severe pain. This medication is available in various forms, including immediate-release and extended-release tablets, and can also be found in combination products with other analgesics like acetaminophen or aspirin.
Oxymorphone is also a potent semi-synthetic opioid, used for the treatment of severe pain. It was first introduced for medical use in the United States in 1959. Like oxycodone, it is available in immediate-release and extended-release oral tablet forms, and was historically available as an injectable and rectal suppository.
Common Ground: Similarities as Opioids
Both oxycodone and oxymorphone are opioid analgesics. Both medications work by binding to opioid receptors located in the brain and spinal cord, which helps to block pain signals and alter the body’s perception of pain. This action on opioid receptors, particularly the mu-opioid receptor, is responsible for their pain-relieving effects and also contributes to their potential for euphoria.
Both oxycodone and oxymorphone are Schedule II controlled substances, indicating a high potential for abuse and the risk of developing physical dependence and addiction. They are both prescribed for the management of moderate to severe pain, whether acute or chronic, when other pain management strategies are insufficient. The side effects associated with these opioids are also broadly similar, commonly including constipation, nausea, vomiting, and drowsiness.
Key Differences in Chemistry and Clinical Application
Oxymorphone exhibits significantly greater potency compared to oxycodone. Studies have shown that oxymorphone can be 12.5 to 14 times more potent than oxycodone when administered intravenously. When taken orally, oxymorphone is also considered more potent per milligram than oral oxycodone or morphine.
The metabolism of these two opioids differs considerably. Oxycodone is primarily metabolized in the liver by two main enzymes: CYP3A4, which converts it into noroxycodone, and CYP2D6, which converts it into oxymorphone. While oxymorphone is an active metabolite of oxycodone and has a higher affinity for opioid receptors, the parent drug, oxycodone, is responsible for the majority of its analgesic effect.
In contrast, oxymorphone is not significantly metabolized by the CYP450 enzyme system, unlike oxycodone. Its primary metabolism occurs through a process called glucuronidation. This difference in metabolic pathways means oxymorphone does not rely on CYP2D6 for activation, which can affect how quickly it works and how long its effects last in different individuals.
Regarding onset and duration of action, immediate-release oxycodone begins to relieve pain within 10 to 30 minutes, with effects lasting up to six hours. For immediate-release oxymorphone, pain relief begins in about 30 minutes after oral administration, with effects lasting approximately 3 to 4 hours. Extended-release formulations of both medications are designed to provide longer-lasting relief for about 12 hours.
Physicians consider these differences, including potency and metabolic pathways, when choosing the appropriate medication for a patient’s pain, especially considering their individual metabolic profile and the nature of their pain.