Tuesday, July 6, 2010

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!

5 comments:

seejanenurse said...

Interesting, just last week my patient was "snowed" from the Dilaudid. The attending was hassling me, I said, "I only gave Dilaudid 2mg." He started questioning me: "Do you realize the Morphine equivalent of that dose?" I had never thought about it. Nice post, and I like to look at your math.

Christopher said...

The math certainly puts things into perspective!

I had a doctor come up to me at 3am in the ED and ask me exactly how much Dilaudid paramedics were allowed to give, because they had a patient who had stopped breathing approximately 5 minutes after the departure of the EMS crew that brought her in!

She had been coming in from BFE and the transport time was actually long enough to give the full 5mg of Dilaudid as allowed by the protocols. It sounds like the paramedic was talking with the patient the whole way to the ED, which is a pretty simple way to ensure somebody is breathing. But once left alone in the room the patient drifted off...

seejanenurse said...

Christopher,

Math helps.

The Dilaudid 5mg is a lot, we are usually running in 2mg or 4mg, sometimes even less depending on the age, weight, pain etc.

We used to be able to just IV push Dilaudid, but pharmacy got the policy changed, it has to be run in piggy back now over 15 minutes. It is a real pain. I personally love morphine because of this, we still push it in straight up.

Yes, breathing is talking. :) When my patients complain of shortness of breath, and are all labored, I just tell them: No more talking. And I get to working. :)

Anonymous said...

Math is great! Also be aware of the difference in oral versus IV equivalents. 10mg of IV Morphine is equivalent to 30mg oral Morphine.
Where morphine equivalents are ME:
[(ME drug #1)/(ME drug #2)]=[(mg drug #1/mg drug #2)]

[(1.5 ME IV hydromorphone)/(10 ME IV morphine)]=[(2mg IV hydromorphone/X mg IV morphine)]

so, 1.5X=20
(20/1.5)=13.3
2mg IV hydromorphone is equivalent to ~13.3mg IV morphine. that's a good dose. especially if the patient is 'opiate naive'.

I don't love this site but it's a handy reference: http://www.globalrph.com/narcoticonv.htm

Christopher said...

Excellent point Anonymous! I have seen folks receive 2 mg Dilaudid over 20-30 minutes and be fine while talking to you, but once you leave them alone they start to have signs CNS depression.