Oxymorphone is a semi-synthetic opioid substitute for morphine. It is a potent analgesic. Opioid analgesics exert their principal pharmacologic effects on the CNS and the gastrointestinal tract. The principal actions of therapeutic value are analgesia and sedation. Opioids produce respiratory depression by direct action on brain stem respiratory centers. The mechanism of respiratory depression involves a reduction in the responsiveness of the brain stem respiratory centers to increases in carbon dioxide tension and to electrical stimulation.
Mechanism of action
Oxymorphone interacts predominantly with the opioid mu-receptor. These mu-binding sites are discretely distributed in the human brain, with high densities in the posterior amygdala, hypothalamus, thalamus, nucleus caudatus, putamen, and certain cortical areas. They are also found on the terminal axons of primary afferents within laminae I and II (substantia gelatinosa) of the spinal cord and in the spinal nucleus of the trigeminal nerve. Also, it has been shown that oxymorphone binds to and inhibits GABA inhibitory interneurons via mu-receptors. These interneurons normally inhibit the descending pain inhibition pathway. So, without the inhibitory signals, pain modulation can proceed downstream.