PERT Program

Tip of the Month: June 2003


Calculating Equianalgesic And Breakthrough Opioid Dosing


To ensure good pain management, it is important for nurses to be skilled in calculating equianalgesic and breakthrough (aka "rescue") dosing of opioids. While nurses are not independently responsible for choosing the dose of a prescribed medication, they are responsible for recognizing and ensuring a proper dose prior to the administration of any drug — including opioids. This requires the ability to interpret an equianalgesic table, calculate a conversion, and advocate for a safe and effective dose to relieve pain.

There are numerous equianalgesic dose tables, many of which are similar to one another. It is helpful to remember that most equianalgesic doses were determined in single-dose studies in young adults. Equianalgesic dosing is not an exact science and may require significant adjustments in the frail elderly. Identifying one table to be used within a given facility will help to ensure consistency while guiding decisions.

The table below has been adapted from the American Pain Society (APS).1 The APS suggests that there is incomplete cross-tolerance when moving from one drug to a second drug; in other words, a patient can be very "used to" one drug but a second drug may be more powerful than expected at equal doses. For this reason, APS recommends that the dose of the new drug be decreased by 30–50% when starting the therapy. Frequent reassessment will help determine when increases are necessary.


Equianalgesic Opioid Doses1
Oral Parenteral
Morphine 30 10
Hydromorphone 7.5 1.5
Oxycodone 20 N/A
Methadone* 20 acute
2–4 chronic 		10 acute
2–4 chronic
Fentanyl Duragesic
(transdermal fentanyl)
25mcg/hr TD =
morphine 50mg po daily		 0.1 mg
Hydrocodone 30** N/A
* Methadone conversion is difficult due to the very long half-life of the drug. Though effective, methadone should only be prescribed by a practitioner experienced in its use.
** There are varying opinions in the literature re: equianalgesic dosing of hydrocodone. The following sources use 30 mg as the equianalgesic dose.[2,3] However, McCaffery [4] reports equianalgesic data as unavailable and therefore not recommended. The Delaware Cancer Pain Initiative suggests Vicodin 5mg/500mg = 9mg po morphine.
(See http://www.endpain.org/dosage.html)


The following is an example of an equianalgesic conversion:

Ms. Graham, age 85, has been taking Percocet (oxycodone 5mg/acetaminophen 325mg) two tablets every 4 hours ATC for pain related to compression fractures in her spine. In the past 24 hours, she has taken all 6 doses of two tabs each. Her pain level remains 5/10 and she often needs to be awakened to take her pills. Her prescriber gives instructions to discontinue the Percocet and begin MS Contin 60mg po BID. Is this an appropriate order?

Using the table above, oxycodone 20mg = morphine 30mg. Ms. Graham has taken 12 Percocet tablets for a total of 60mg of oxycodone in the past 24 hours. An equianalgesic ratio looks like this:



The straight-across conversion would be 90mg morphine/24 hours. However, it is prudent to decrease this dose by 30% because even though her pain is not well controlled, it is unknown how Ms. Graham will tolerate morphine. A 30% decrease in the 90mg dose would equal 63mg. Rounded off this would mean 60mg/24 hours, or 30mg po bid. Therefore a more reasonable dose of MS Contin would be 30mg po bid, which is ½ the amount prescribed. It would be important to discuss this with the prescriber, explaining the rationale of incomplete cross-tolerance discussed above.

All residents who are on chronic opioid therapy should have an immediate-release medication available to treat "breakthrough" or "incident" pain. It is recommended that the same category of medication be used as that of the sustained-release drug, and that it be available every 2 hours prn. It is also recommended that each breakthrough dose be 10–30% of the 24-hour opioid dose. In Ms. Graham's case, her newly prescribed 24-hour dose of 60mg MS Contin would warrant an order for 6–18mg morphine q 2hr prn. Accordingly, a good starting amount of immediate-release morphine would be 10mg per dose.

Becoming skilled at opioid dose conversion and calculation is an important part of providing good pain management. You might want to practice by taking the daily opioid requirement of a current resident and calculating an equianalgesic conversion to a new opioid. Ask a colleague to do the same, and compare results!

Questions? Feel free to contact the PERT Program. We will be happy to consult with our pain experts to provide further information.



References

  1. Principles of analgesic use in the treatment of acute pain and cancer pain. 4th ed. Glenview, IL: American Pain Society; 1999.
  2. Wrede-Seaman L. Symptom management algorithms for palliative care. American Journal of Hospice & Palliative Care. 1999;16(3):517-526.
  3. American Medical Directors Association. Chronic pain management in the long-term care setting. Columbia, MD: American Medical Directors Association; 1999.
  4. McCaffery M, Pasero C. Pain clinical manual. 2 ed. St. Louis: Mosby, Inc.; 1999.