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14 Articles in Volume 18, Issue #9
Assessing Arthralgia in Children
Children, Opioids, and Pain: The Stats & Clinical Guidelines
How to Fit into a New Practice
How to Talk to Your Chronic Pain Patients
How to Treat Opioid Use Disorder in Pregnant Women
Intranasal Ketamine for Acute Pain in Children
Medication Selection for Comorbid Pain Management (Part 3)
MR Neurography: Using Peripheral Nerve Imaging as a Pain Diagnostic
Naloxone in Schools; Buprenorphine Conversions; OUD Management
Opioid Conversion Calculations and Changes
Pes Anserine Tendino-Bursitis as Primary Cause of Knee Pain in Overweight Women
Self-Management of Chronic Pain in Primary Care
The Homebound Adolescent: Managing Chronic Pain Conditions in the Pediatric Population
The Opioid Band-Aid: The State of Pain Pills, Congressional Bills, and Healthcare in the US

Opioid Conversion Calculations and Changes

An excerpt from the new book, Demystifying Opioid Conversion Calculations: A Guide for Effective Dosing.
Pages 43-44
Page 1 of 2

(Source: Courtesy of the Publisher)

Mary Lynn McPherson, PharmD, MA, MDE, BCPS, a professor of pharmacy practice and science at the University of Maryland School of Pharmacy in Baltimore, MD, has released the second edition of her book, Demystifying Opioid Conversion Calculations: A Guide for Effective Dosing. Her book has long been a go-to guide for clinicians involved in pain management at all levels as well as those learning how to calculate opioid conversions (see PPM's free online calculator). The revised edition focuses on the calculations that providers use in actual practice, including realistic scenarios for decision-making. Below is an excerpt* from the book focusing on when to change an opioid prescription.

Ah,...drug math. Those two little words can make a strong healthcare professional clench their bowels and want their mommy. But, this doesn’t have to be the case! Armed with an understanding of conversion calculations, some semisolid facts about equivalencies, and a healthy sense of “Does that look right?” you’ll be just fine! Just like much of healthcare, there is both science and art involved in performing opioid conversion calculations… so jump in; the water’s fine!

Opioids are the mainstay of pain management in patients with moderate-to-severe pain. Morphine is practically mother’s milk to practitioners who work with patients with advanced illness due to its familiarity, availability of multiple dosage formulations, low cost, and proven effectiveness. However, morphine is not always the answer. For example, we know that up to 30% of cancer patients show poor responsiveness to a given opioid such as morphine during routine administration.1 This is only one reason why healthcare practitioners must be able to transition patients from one opioid to another, which may require changing the route of administration and/or dosage formulation. A recent multicenter study conducted with palliative care patients showed that 12% of patients required a change to a different opioid (not counting a change in route of administration) for reasons including lack of pain control (64%), development of adverse effects (51%), and medication application problems (22%).2 Let’s take a closer look at the clinical situations that result in the need to switch a patient from one opioid to another.


Reasons For Changing Opioids 

Lack of Therapeutic Response

If the patient’s pain is not responding adequately to the opioid and a repeat assessment indicates that opioid therapy continues to remain appropriate, a dose increase would be the most likely intervention. The increase in pain may be due to disease progression or the development of opioid analgesic tolerance. If the patient cannot tolerate an increase in dose due to the development of adverse effects or an increase in dose does not produce a satisfactory reduction in pain, switching to a different opioid may be beneficial.

Occasionally, a patient is receiving a combination analgesic (eg, Percocet, which contains oxycodone and acetaminophen), and an increase would exceed the maximum recommended daily dose of acetaminophen (4 g). In this case, switching to a tablet or capsule containing just oxycodone would be appropriate, with subsequent dosage titration.

Development of Adverse Effects

If the patient develops an adverse effect to an opioid, the healthcare professional must consider plan B. Opioid-induced adverse effects are well recognized and include the following:

  • Gastrointestinal (nausea, vomiting, constipation)
  • Autonomic (xerostomia, urinary retention, postural hypotension)
  • Cutaneous (pruritus, sweating)
  • Central nervous system (sedation, confusion, dizziness, hallucinations, delirium, myoclonus,
    hyperalgesia, seizures, and respiratory depression)
  • Rarely, opioid allergy (rash, hives, difficulty breathing) may occur.

Faced with an opioid-induced adverse effect, management options may include the following:

  • Reduction of opioid dose if pain is adequately controlled (monitor patient response carefully)
  • Aggressive management of the opioid-induced toxicity
  • Addition of a non-pharmacologic intervention or co-analgesic to allow reduction of the opioid dose
  • Switching to a different route of administration to minimize adverse effect
  • Switching to a different opioid that will hopefully be better tolerated and at least as effective.

Change in Patient Status

As patients with advanced illness decline, they may not be able to tolerate or use their current opioid formulation or route of administration. For example, a patient may develop difficulty swallowing (dysphagia) or pain with swallowing (odynophagia). Although somewhat controversial, patients who are very cachectic or who have poor peripheral circulation may not receive the fully expected benefit of a transdermally delivered opioid. On the other hand, a transdermal patch may be more convenient for, and acceptable to, the patient or family, and switching would enhance quality of life. A patient may require a very high dose of an oral, rectal, or transdermal opioid, necessitating a change to parenteral therapy. Conversely, a patient being discharged home who is able to swallow would likely prefer oral opioid therapy over parenteral.

Other Considerations

Availability of the opioid and/or particular formulation at the patient’s pharmacy, cost, and formulary issues may influence prescribing. Medication insurance does not cover all opioid formulations, so a switch may be necessary.

Patients, families, and caregivers may hold healthcare beliefs about certain opioids that affect prescribing such as a previous bad experience with a particular opioid (eg, severe nausea or vomiting) or a stigma associated with a particular opioid (eg, “Isn’t morphine just for dying patients?” or “Isn’t methadone only used by drug addicts?”). An unfortunate reality of practice today is that of drug shortages, which necessitates a switch to a therapeutic alternative. In addition, community pharmacies may unexpectedly reach their monthly allocation of a particular opioid from the wholesaler before reaching the end of the month. If the patient is unable to find their particular opioid, this may require a switch as well.

Drug abuse and diversion is also a harsh reality in today’s society, by the patient, a family member, or a visitor to the patient’s home. In home-based hospice, for example, practitioners often need to switch to a hopefully less-abused opioid formulation such as transdermal fentanyl and limit quantities kept in the home. This is one example of a risk-mitigation strategy.

Last updated on: December 3, 2018
Continue Reading:
Practical Guide to the Safe Use of Methadone