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12 Articles in Volume 17, Issue #1
A Brief History of the FDA’s Role in the Ongoing Effort to Ensure Safe Opioid Use
Distinguishing Neuropathic, Non-Neuropathic, and Mixed Pain
How Can Healthcare Providers Better Advocate for Patients With CRPS?
Ketamine for the Treatment of CRPS?
Letters to the Editor: Opioid Calculator; Metformin
Living With CDC Opioid Guidelines
Neurohormones in Pain and Headache Management: New and Emerging Concepts
Optimizing Neuropathic Pain Relief With Scrambler Therapy
Pain Management and the Elderly
Spinal Cord Stimulation: What Clinicians Need to Know
The Association Between Depressive Disorder and Chronic Pain
Updates in Management of Complex Regional Pain Syndrome

Letters to the Editor: Opioid Calculator; Metformin

January/February 2017

Opioid Calculator

I have a question about the opioid calculator for research purposes. I am curious if the calculator takes into consideration half-life? Can you tell me about validity and reliability testing of this calculator?

 Shirley Martin, PhD, RN

Dear Shirley,

We do not consider half-life because the conversion is based either on 1-time dosing (selection choice #1) or chronic daily dosing (selection choice #2). Presumably, in a patient who is taking around-the-clock medication and has reached a steady state, half-life will not be an issue. 

Where half-life does become an issue is during the transition; that is, one needs to consider the half-life of both drugs—old and new, how quickly to convert, and whether or not opioid overlap is necessary. This last question is very important for drugs such as methadone, which has a very long and variable half-life plus a high volume of distribution. 

Responses to reader questions about the opioid calculator and metformin.Another consideration is with conversion, taking into account pharmacogenomics and drug interactions. To the best of my knowledge, no calculator takes these factors into consideration, and it is a flaw of opioid conversion overall.1

Nevertheless, I believe that the PPM Calculator is the most comprehensive and the first to incorporate the “Fudin Factor,” as in methadone conversion. For an explanation of this, I suggest reading Mathematical Model for Methadone Conversion Examined.2

Regarding validation, that was done internally and has not been done by an external source. Also, I do not believe that any calculators are validated—and the simple truth is, none are “valid” per se because there is no universally accepted opioid conversion on which to base any other factors, as outlined in the MEDD myth1 article referenced above.

I hope this is helpful,
Jeffrey Fudin, PharmD

Anti-Inflammatory Action of Metformin

I am a chronic pain patient in the pain management program at Sheboygan Aurora Hospital. I have had 3 spinal surgeries and my back is fused at L2-5. I suffer from permanent nerve damage in my lower back and down both legs into my toes. Thirteen months ago, I had to take metformin to control my insulin levels per my endocrinologist as I was diagnosed with prediabetes. Having made lifestyle adjustments, including a low-carb diet and light treadmill walking, I have lost 24 pounds. However, the AMAZING thing is that I noticed I could press into my legs and I didn’t go through the roof from excruciating pain as I did in the past. Even when taking my methadone and hydrocodone, I would press my legs and it hurt like ****.

I believe that the metformin has relieved the nerve pain in my legs. What do you think?

  Brian Karth    
Sheboygan, Wisconsin

Dear Brian,

The notion that metformin has helped your pain is to be expected, rather than a surprise. Metformin belongs to a class of treatment agents that I like to call “microglial suppressors.” Other common agents in this class are pentoxifylline, minocycline, and acetazolamide. In recent years, basic science researchers have developed techniques to determine if a drug will suppress the microglial cell (the inflammatory cell in the central nervous system), thereby reducing neuroinflammation in the spinal cord and brain. After a 4-level lumbar fusion, it would be expected that the nerve roots in your cauda equina would have some microglial activation and neuroinflammation, which would produce symptoms such as radiating pain, bladder impairment, and inability to sit or stand in one position for an extended period of time. Metformin not only will suppress neuroinflammation, it may also alter insulin and glucose metabolism in your central nervous system and the nerves in your legs.3-5

Your story is most appreciated and educational. Metformin is an old drug that has stood the “test of time” for safety and efficacy. In my practice, it is now a first-line pain treatment with a recommended starting dose of 500 mg at bedtime. I find that metformin fits well into most pain control regimens and protocols to help reduce the need for opioids.

Thanks for the story,
Forest Tennant, MD, DrPH

Last updated on: February 14, 2017
Continue Reading:
Pain Management in the Elderly

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