What is the explanation of oral morphine (opioid analgesic) equivalent?

From the Guidelines

Oral morphine equivalent (OME) is a crucial concept in pain management, allowing healthcare providers to compare the potency of different opioid medications and ensure safe switching between them, with the most recent and highest quality study 1 providing the necessary conversion factors. When calculating OME, it is essential to consider the relative potency of each opioid compared to morphine. According to the study 1, the conversion factors for common opioids are as follows:

• Oral morphine: 1
• Oral oxycodone: 1.5-2
• Oral hydromorphone: 7.5
• Transdermal fentanyl: +4 (depending on the dose) To calculate OME, multiply the dose of the opioid by its conversion factor. For example, 30mg of oral morphine is equivalent to 20mg of oral oxycodone, 7.5mg of oral hydromorphone, or 0.3mg of transdermal fentanyl. Some key points to consider when using OME:
• The conversions are estimates, and individual patient responses may vary based on factors like tolerance, metabolism, and cross-tolerance between different opioids 1.
• When switching between opioids, providers typically reduce the calculated equivalent dose by 25-50% to account for incomplete cross-tolerance and minimize adverse effects, then titrate as needed for pain control 1.
• The average relative potency ratio of oral to subcutaneous morphine is between 1:2 and 1:3, as stated in the study 1. By using OME and following these guidelines, healthcare providers can ensure safe and effective pain management for their patients.

From the FDA Drug Label

The FDA drug label does not answer the question.

From the Research

Oral Morphine Equivalent Explained

• The concept of oral morphine equivalent is used to estimate the dose of an opioid required for different clinical situations, based on the equianalgesic potency of opioids 2.
• One oral morphine equivalent is the analgesic dose of an opioid (orally administered) equal to the analgesic effect of a specific dose of oral morphine.
• The relationships between equianalgesic doses and oral routes of applications are listed in tables, and cross-tolerance between different opioids during long-term treatment is not complete 2.
• To avoid an overdose, a reduction in the calculated opioid dose of 50% is suggested, with additional "rescue doses" used during the period immediately after changing opioids or routes of administration 2.

Factors Affecting Oral Morphine Equivalent

• Individual differences in response to opioids, especially during long-term treatment and in the development of analgesic tolerance, can affect the oral morphine equivalent 2.
• Individual differences in response to alternative routes of administration can also impact the oral morphine equivalent 2.
• The unknown degree of cross-tolerance among opioid drugs is another factor to consider when estimating oral morphine equivalents 2.

Clinical Applications of Oral Morphine Equivalent

• Oral morphine equivalents can be used to convert one opioid dose to another, taking into account the equianalgesic potency of different opioids 3.
• This conversion can be useful in clinical practice, particularly in the emergency department, where patients may require rapid pain relief 3.
• Oral morphine equivalents can also be used to compare the efficacy and tolerability of different opioids, such as oral morphine and oxycodone/acetaminophen, in the treatment of acute pain 4.