Converting between modes of administration or between opioids often becomes necessary due to disease progression, uncontrolled pain, or intolerable side effects. Most equianalgesic conversion data are based on older, single-dose studies, and there is wide variability in conversion ratios reported in the literature.
Opioid conversions should be performed on an individual basis, using dosage conversion tables as a general guide only. Close followup of patient response if necessary. Commonly used conversions:
Drug: Morphine
Oral/Rectal: 30mg
IV/SC: 10mg
Drug: Oxycodone
Oral/Rectal: 20mg
IV/SC: n/a
Drug: Hydromorphone
Oral/Rectal: 7.5mg
IV/SC: 1.5mg
Drug: Codeine
Oral/Rectal: 200mg
IV/SC: 120 (IM only)
Drug: Hydrocodone
Oral/Rectal: 30mg
IV/SC: n/a
Drug: Oxymorphone
Oral/Rectal: 10mg
IV/SC: 1mg
Drug: Fentanyl
Oral/Rectal: n/a
IV/SC: 100mcg (single dose)
Dose Route Conversions
Converting between routes of administration is often necessary due to uncontrolled pain or disease progression. For example, conversion from intravenous PCA administration to oral route may be necessary after hospital discharge. Conversely, when patients can no longer swallow oral medications, continuous subcutaneous infusion or intravenous delivery are safe and effective alternative ways to administer medication. Intramuscular injections are painful and usually unnecessary.
Practice dose conversions with the following examples (click here for Help with Dose Conversions).
Judy, a 54-year-old female with metastatic lung cancer, is hospitalized with pneumonia and inadequate pain control. She is started on morphine PCA with 0.5mg/hour basal infusion plus bolus dosing, which provides good pain control. In addition to the basal rate, Judy requires 28mg of morphine via PCA over a 24 hour period. What is the equivalent oral dose of extended-release morphine (given every 12 hours) for Judy? Here is the answer.
Michael, a 75-year-old male with end-stage renal failure, is no longer able to swallow medication. He is under the care of a home hospice agency. His pain was previously well controlled on 45mg extended-release morphone orally every 12 hours. What is the proper hourly dosage rate if converting Michael to a continuous subcutaneous infusion? Here is the answer.
Opioid Rotation
Converting between opioids is often necessary due to limitations of formulary, insurance, and medication availability. Conversion can also be utilized when patients experience unacceptable side effects associated with opioid treatment. Often a patient may experience more effective analgesia from a lower-than-equivalent dosage of another opioid. This phenomenon is known as incomplete cross-tolerance and is thought to be due to differences in opioid receptor affinities. When converting opioids, the relative dosage of the new agent can often be decreased by 25% to 50% to adjust for cross-tolerance.
Practice opioid conversions with the following examples: Rebecca, a 27-year-old female with AIDS, is no longer able to swallow and is experiencing myoclonic jerks with morphine. Her pain was previously well controlled on extended-release morphine 90mg every 12 hours and short-acting morphine 10mg every four hours. The goal is to transfer the patient over to a continuous subcutaneous infusion of hyromorphone. What is the hourly rate, if we correct for cross-tolerance by 50%? Here is the answer.
John, a 69-year-old male with laryngeal cancer and radiation esophagitis, has been treated with a hyrdomoprhone PCA pump. His pain is well controlled at 0.2mg/hour. Correcting for cross-tolerance by 25%, what would be the proper dose of extended release oxycodone (12-hour dosing)? Here is a bonus item: What dose of short-acting oxycodone would you suggest for breakthrough pain? Here is the answer.