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Dosage differences depending on the route of administration, dosage variations between medications, and the overall status of the patient are some of the factors that physicians consider when calculating opioid conversions. Opioid conversion tables provide duration, half-life, route, and dosage adjustments between medications. Other factors not considered by these tools include dosage differences between regular and extended release forms of the same medications, specific medical conditions, or a change in patient status while taking the prescribed medication.
Physicians generally prescribe opioid medications for acute pain that follows surgical procedures or for moderate to severe chronic pain associated with arthritic conditions or cancer. Types of opioids commonly used include true opioids, semi-synthetic opioids, and synthetic opioids. Codeine and morphine contain 0.50% and 10% of opium, respectively, while oxycodone and oxycontin contain morphine and acetyl or other manmade compounds. Synthesized opioids include fentanyl and methadone.
The time in which patients experience the pain relief produced by opioids differs markedly depending on whether drug administration is oral, intramuscular, or intravenous (IV). Medication given IV infusion reaches the bloodstream immediately and generally requires a lower dose than other forms of the same medication. Patients prescribed IV opioid therapy in a hospital setting may continue the medication orally after discharge, which generally requires opioid conversion. Physicians may prescribe an extended release formula for patients who aren't receiving adequate pain control on routine doses of a regular formulation, which might require dosage adjustments because of the size of the patient or the intensity of the pain.
Patients who experience adverse reactions to one opioid medication might be switched to a different drug. Likewise, patients who react to the adhesive of a transdermal patch used to administer opioids may require a different form of the medication and accompanying dosage adjustment. Differences in potency generally require opioid conversion. Patients taking 200 milligrams (mg) of codeine orally every four to six hours only need 20 to 30 mg of hydrocodone every four to eight hours. Oral doses of oxymorphone may start at 10 mg every three to six hours.
After long-term use of opioids for chronic pain, a patient often develops a tolerance for the medication or the patient's pain may increase as their condition deteriorates. Both circumstances requires a stronger opioid for adequate pain management and might require opioid conversion between two different medications. Some patients suffer from hepatic or renal insufficiency, and typical oral dosages may cause an overdose, as their body cannot effectively eliminate the medication. Opioid conversion might be required under these circumstances as well.
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