Equianalgesic Doses

Equianalgesic dose calculation guidelines

Case

Jack Smith is a terminally ill lung cancer patient. Jack Smith’s current pain medication is oxycontin 40mg q 8 hours. Please convert it into an equianalgesic dose of parenteral hydromorphone.

Step 1

First determine total 24 hour dose of current drug. The total dose is the product of the unit dose in milligrams and the frequency of administration.

Current unit dose = 40 milligrams
Current frequency = 3
(pt gets the drug every eight hours which is 3 times in 24 hours)
24 hour total dose of oxycodone = Unit dose in milligrams x Frequency
Current 24 hour total dose of oxycodone = 40mg x 3 = 120mg

 

Step 2

Convert total 24 hour dose of current drug to equianalgesic dose of ORAL morphine using the following guidelines:

24 hour dose of current drug in milligrams

Conversion ratio to ORAL morphine

Equivalent dose of ORAL morphine

60mg of parenteral morphine Parenteral morphine is three times as potent as oral morphine 180 milli grams Oral morphine
120 mg of oral oxycodone Oral Oxycodone is roughly 1.5 times more potent than oral morphine 180 milli grams Oral morphine
45 mg of oral hydromorphone Oral hydromorphone is 4-7 times as potent as oral morphine 180 milli grams Oral morphine
9mg of parenteral hydromorphone Parenteral hydromorphone is 20 times as potent as oral morphine 180 milli grams Oral morphine
45mg of oral hydrocodon Oral hydromorphone is roughly five times as potent as oral morphine (4 to 7 times more potent) 180 milli grams Oral morphine
1800 micrograms (1.8 milligrams) over 24 hours. Therefore hourly dose is 75 micrograms/hour. Transdermal fentanyl is 100 times as potent as morphine 180 milli grams Oral morphine

 

Current 24 hour total dose of oxycodone = 40mg x 3
= 120mg
Oral Oxycodone is roughly 1.5 times more potent than oral morphine.
Therefore, equianalgesic dose of oral morphine = oxycodone dose in milligrams x 1.5
= 120mg x 1.5
= 180mg of oral morphine

Step 3

Convert the calculated 24 hour equianalgesic dose of oral morphine to the 24 hour equianalgesic dose of the new opioid:

Calculated 24 hour equianalgesic dose of oral morphine = 180mg
Parenteral hydromorphone is 20 times as strong as oral morphine.
Therefore 180mg of oral morphine = 180/ 20 mg of parenteral hydromorphone
= 9mg of parenteral hydromorphone

 

Step 4

Divide the 24 hour dose of the equianalgesic dose of the new opioid to determine the unit doses and frequency:

Calculated 24 hour dose of hydromorphone = 9mg
Hourly dose of parenteral hydromorphone = Calculated 24 hour dose/ 24
= 9mg/24
= 0.375mg/hour

 

The case:

Jack Smith is a terminally ill lung cancer patient. Jack Smith’s current pain medication is Morphine sulfate sustained release 45mg every 12 hours. During a clinic visit, Mrs. Smith complains that she has noticed that her husband has developed muscle twitching ever since his Morphine sulfate sustained release was increased to 45mg every 12 hours. You review Mr. Smith’s recent chemistry panel and note that his creatinine is elevated at 2.4. Please convert the transdermal fentanyl into an equianalgesic dose of long acting oxycodone.

Sequential steps

Sequential steps

Process

Answer

First determine total 24 hour dose of current drug. The total dose is the product of the unit dose in milligrams and the frequency of administration in 24 hours.

In this case:

Unit dose = 45mg

Frequency of administration = 2 times in 24 hours

Therefore total dose = Unit dose x frequency = 45 x 2= 90mg

Patient is currently on 90mg of Morphine sulphate.
Convert total 24 hour dose of current drug to equianalgesic dose of ORAL morphine. Current drug in this case is Morphine sulfate. 4 hour equianalgesic dose = 90mg of morphine sulfate.
Convert the calculated 24 hour equianalgesic dose of oral morphine to the 24 hour equianalgesic dose of the new opioid. Oxycodone is the preferred drug in this case as it is renally safer than morphine. Oxycodone is thought to be 1.5 times stronger than morphine.
Therefore, Morphine sulfate 90mg is equianalgesic to oxycodone 60mg
24 hour equianalgesic dose of the new opioid (oxycodone) = 60mg
Divide the 24 hour dose of the equianalgesic dose of the new opioid to determine the unit doses and frequency. Similar to morphine, oxycodone is available in a sustained acting preparation Oxycodone (OxyContin™) that can be dosed every 12 hours. In this case Oxycodone 60mg in 24 hours can be divided into a unit dose of 30mg to be given every 12 hours. Final order for basal analgesic should read:

Oxycodone sustained release every 12 hours for chronic pain.

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