Morphine Equivalents

A pretty hot topic lately has been prehospital pain control and how for the most part it is viewed as a failure. Granted, the perception of how well prehospital providers handle pain control is not what I'm looking to talk about, Rogue Medic and the bloggers at Paramedicine 101 have touched on this topic quite a number of times.

What I'd like to do is add a little math to the discussion. Over at Street Watch: Notes of a Paramedic there is an excellent post about a new study on Fentanyl versus Morphine combined with a more liberal pain control protocol. The protocol mentioned "Morphine Equivalents," something of which I was only tangentially aware.

"Morphine Equivalents" are basically a unit of measure used to compare the efficacy of opiods. After a trivial amount of Googling I came across an easy to follow guide from the University of Alberta's Multidisciplinary Pain Centre which listed conversion factors between various opiods. Using these conversion factors, we could compare how equivalent various pain control protocols are.

In North Carolina our 2009 EMS protocols allow 3 opiods for the treatment of pain: dilaudid, morphine, and fentanyl. Per the conversion guide, these drugs compare as follows:

• 1 mg of Fentanyl is equivalent to 100 mg of Morphine
• 1 mg of Dilaudid is equivalent to 5 mg of Morphine

So let's examine the 2009 NC Protocols for Pain Control:

• Morphine: 4 mg IM/IV/IO bolus, may repeat with 2 mg every 3-5 minutes to a max 10 mg or clinical improvement
• Fentanyl: 50-75 mcg IM/IV/IO bolus, may repeat with 25 mcg every 20-30 minutes to a max 200 mcg or clinical improvement
• Dilaudid: 1-2 mg IM/IV/IO bolus, may repeat with 1 mg every 20-30 minutes to a max 5 mg or clinical improvement

Now let's do the conversion to Morphine Equivalents (MSeqv hereafter):

• Fentanyl: 5-7.5 MSeqv bolus, may repeat with 2.5 MSeqv every 20-30 minutes to a max 20 MSeqv
• Dilaudid: 5-10 MSeqv bolus, may repeat with 5 MSeqv every 20-30 minutes to a max 25 MSeqv

Both the Fentanyl and Dilaudid protocols allow for a higher loading dose in Morphine Equivalents. They both offer a much higher maximum dosage as well. However, if we look at the rebolus schedule they compare poorly to Morphine. Fentanyl's maintenance schedule is 5x weaker, and Dilaudid's is 2.5x weaker than the equivalent Morphine schedule.

Moreover, when you compare the amount of Morphine Equivalents per minute allowed by the protocol, assuming you had the maximum time required to deliver each medication, you find both Fentanyl and Dilaudid compare poorly to Morphine:

• Morphine: 0.8 MSeqv/minute (max reached in 12 minutes)
• Fentanyl: 0.2 MSeqv/minute (max reached in 120 minutes)
• Dilaudid: 0.3 MSeqv/minute (max reached in 80 minutes)

Take this with a huge grain of salt, because this mathematical comparison does not take into account bioavailability, half-life, side effects, rate of administration, and probably a whole host of other important factors. However, what this comparison does show is that while pain control protocols have improved and prehospital providers have options, they aren't all necessarily equal!

Updated 20 July 2010: For a visual representation of their "strength of schedule" see Morphine Equivalents Visualized.