indication

For the treatment of moderate-to-severe pain.

pharmacology

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.

toxicity

Oxymorphone overdosage is characterized by respiratory depression, extreme somnolence progressing to stupor or coma, skeletal muscle flaccidity, cold and clammy skin, and sometimes bradycardia and hypotension. In a severe case of overdose, apnea, circulatory collapse, cardiac arrest, and death may occur. Intravenous mouse LD₅₀ is 172 mg/kg.

biotransformation

Oxymorphone undergoes extensive hepatic metabolism in humans. After a 10 mg oral dose, 49% was excreted over a five-day period in the urine. Of this, 82% was excreted in the first 24 hours after administration. The recovered drug-related products contained the oxymorphone (1.9%), the conjugate of oxymorphone (44.1%), the 6(beta)-carbinol produced by 6-keto reduction of oxymorphone (0.3%), and the conjugates of 6(beta)-carbinol (2.6%) and 6(alpha)-carbinol (0.1%).

half life

1.3 (+/-0.7) hours

route of elimination

Oxymorphone is highly metabolized, principally in the liver, and undergoes reduction or conjugation with glucuronic acid to form both active and inactive products. Because oxymorphone is extensively metabolized, <1% of the administered dose is excreted unchanged in the urine.

drug interactions

Cimetidine: Increases the effect of the narcotic

Triprolidine: The CNS depressants, Triprolidine and Oxymorphone, may increase adverse/toxic effects due to additivity. Monitor for increased CNS depressant effects during concomitant therapy.