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Many of the effects described below are common to the class of opioid analgesics, including NUMORPHAN (oxymorphone) .
Central Nervous System (CNS)
Opioid analgesics exert their principal pharmacologic effects on the CNS and the gastrointestinal tract. The principal actions of therapeutic value are analgesia and sedation. The precise mechanism of the analgesic action is unknown. However, specific CNS opiate receptors have been identified and likely play a role in the expression of analgesic effects.
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. Opioids depress the cough reflex by direct action on the cough center in the medulla. Opioids cause miosis. Pinpoint pupils are a common sign of opioid overdose but are not pathognomonic. Marked mydriasis may be seen with worsening hypoxia.
Gastrointestinal Tract and Other Smooth Muscle
Opioids decrease gastric, biliary, and pancreatic secretions. These drugs cause a reduction in motility associated with an increase in tone in the antrum of the stomach and duodenum. Digestion of food in the small intestine is delayed and propulsive contractions are decreased. Propulsive peristaltic waves in the colon are decreased while tone is increased to the point of spasm. The end result is constipation. Opioids can cause a marked increase in biliary tract pressure as a result of spasm of the sphincter of Oddi.
Opioids increase smooth muscle tone in the urinary tract and can induce spasms. Urinary urgency and difficulty with urination may result. These effects, in conjunction with the central effect of these drugs on release of vasopressin, may produce oliguria.
The onset of action of parenterally administered NUMORPHAN (oxymorphone) is rapid; initial effects are usually perceived within 5 to 10 minutes. Its duration of action is approximately 3 to 6 hours.
Distribution: After an IV dose, the steady state volume of distribution was 3.08 ± 1.14 L/kg in healthy male and female subjects.
Metabolism: 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 6β-carbinol produced by 6-keto reduction of oxymorphone (0.3%), and the conjugates of 6β-carbinol (2.6%) and 6α-carbinol (0.1%).
Elimination: In healthy subjects, the mean terminal half-life of oxymorphone was 1.3 ± 0.7 hours. The mean systemic clearance was 2.0 ± 0.5 L/min.
Last reviewed on RxList: 6/24/2008
This monograph has been modified to include the generic and brand name in many instances.
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