Toxicity
In common with other opioids, 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.
At equianalgesic doses oxymorphone is marginally more toxic than morphine but less so than fully synthetic opioids such as methadone and pethidine. At therapeutic doses, toxicity is primarily manifested as miosis, nausea, and possibly occasional mild involuntary muscle movements especially in the distal portions of the extremities and the shoulder area in some cases. This is most common in patients taking a number of other drugs for their condition, especially muscle relaxants and some adjuvant analgesics, and also appears to happen most often during and immediately after a significant upward titration in the single-dose and per 24 hour doses.
Instances of the body suddenly jerking bolt upright from a more relaxed sitting position is a sign of high and/or rapidly increasing serum levels of opioids and all of the above movements are likely due to the anticholinergic or anticholinergic-like effects of opioids and/or other medications prescribed at the same time, as they manifest in patients on atropine-like drugs as well. The primary risk here involves dropping objects, spilling liquids, striking body parts against walls, and potentially losing footing on flat ice surfaces.
While all this can be frightening at first, more than 85 percent of patients do not experience it at any time during treatment, and oxymorphone does not appear to induce seizures in neurologically healthy patients as does the pethidine series of opioids (pethidine, anileridine, alphaprodine, piminodine and others) nor does it have toxic metabolites that accumulate in the system as do pethdine synthetic opioids. There is also no real evidence that oxymorphone significantly lowers the seizure threshold like tramadol and some of the other synthetics mentioned above.
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