What Are Opioid Equivalents and Conversions?

Switching patients from one opioid painkiller to another may be necessary for many reasons, whether cost, drug availability or the patient developing a tolerance. Opioid equivalents and conversions charts allow doctors to switch drugs while maintaining the same level of painkilling effectiveness and avoiding overdosing the patient.

Opioids are chemical compounds with properties similar to opium, a substance obtained from the seed pods of Papaver somniferum species of poppy. Opioids have medicinal benefits as well as addictive properties.

Opium contains substances such as morphine and codeine, which are potent pain relievers (analgesics). Prescription opioids are medications that may be semi-synthetic substances prepared by extracting the alkaloid compounds from opium, or wholly synthetic products with opioid properties.

Opioids are usually prescribed for pain relief (analgesia) only when non-opioid medications do not adequately control pain. The initial regimen for pain management is typically a non-steroidal anti-inflammatory drugs (NSAIDs) or acetaminophen. Opioids are prescribed for the management of:

• Acute pain
• Chronic nonmalignant pain
• Cancer-related pain

Opioids bind to certain proteins known as opioid receptors on the surface of the nerve cells in the brain, spine and other parts of the body. Opioids inhibit the release of neurotransmitters from the nerve cells and block the transmission of pain signals. Opioids also activate the pleasure centers of the brain and produce a sensation of euphoria.

The important steps to be taken before opioid prescription include the following:

• Assessment of pain level
• Evaluation of the patient to find
  • Cause of the pain
  • Coexisting conditions (comorbidities)
  • Other medications taken
• Selection of appropriate opioid and dosage based on individual requirement

The recommendations issued by the Centers for Disease Control and Prevention for opioid prescription by clinicians to manage chronic pain include the following:

Clinicians should

• Try nonopioid (NSAIDs) and nonpharmacologic therapies (physical therapy) as the first line of treatment and prescribe opioids only if expected benefits for pain and function outweigh the risks involved. Where possible opioid use must be minimized by combining with nonopioid and nonpharmacologic therapy.
• Establish treatment goals and continue opioid therapy only if there is meaningful benefit and improvement in the patient’s pain and function.
• Discuss with the patient and keep them aware of the realistic benefits and risks of opioid therapy, before initiation and periodically during the therapy.
• Initiate therapy for chronic pain with immediate-release opioids instead of extended release/long-acting opioids.
• Initiate therapy with the minimum possible dosage and try to maintain it at the lowest effective dosage.
• Prescribe the lowest possible effective dosage of immediate-release opioid for acute pain, for the minimum duration possible.
• Evaluate benefits and harm to the patient within 4 weeks after initiation of opioid therapy and at least every three months thereafter. Opioids should be tapered or discontinued if benefits do not outweigh harm to the patient.
• Evaluate risk factors and incorporate strategies to mitigate the risks. Risk factors in patients include:
  • History of overdose
  • History of substance use disorder
  • Higher dosage of opioid use
  • Concurrent use of benzodiazepine
• Review every three months or at every prescription, the patient’s history of controlled substance prescriptions using state prescription drug monitoring program (PDMP) data, to determine overdose risks.
• Perform urine drug testing before initiating opioid therapy and test annually thereafter to assess use of prescription and illicit drugs.
• Avoid concurrent use of opioid pain therapy and benzodiazepines.
• Offer or arrange medication-assisted treatment with buprenorphine or methadone in combination with behavioral therapies, for patients with opioid use disorder.

Opioid equivalents are different formulations of opioid medications that can be used to produce approximately equal analgesia. The “equianalgesic” doses are calculated based on the individual opioid potencies. A published equianalgesic chart provides equivalent doses of different opioids for different routes of administration. The opioid doses are calculated in oral morphine equivalent units.

Opioids may be administered in the following routes:

• Oral
• Injection (intravenous [IV], subcutaneous [SC], intramuscular [IM])
• Skin (transdermal) patches

Conversions of opioids can be in one of the following ways:

• Different opioid, same route of administration
• Same opioid, different route of administration
• Different opioid, different route of administration

Opioids are rotated to improve analgesic effects when optimal doses do not provide adequate pain relief. Increased opioid doses may cause severe side effects. Conversion to an equivalent dose of a different opioid can improve analgesia and help lower the risk of side effects.

Patients who take opioids for chronic pain on a long-term basis develop tolerance to the opioids, and start requiring higher dosages to achieve pain relief. Patients also develop cross-tolerance to other related opioids, but cross-tolerance is most often not complete, and a rotation is usually beneficial.

The reasons for opioid rotation include:

• Inadequate pain relief from current opioid
• Unmanageable side effects
• Change in patient’s condition such as liver or kidney problems, which require a change of medication
• Drug availability and costs
• Interaction with other drugs the patient may be taking
• Managing breakthrough pain (pain that occurs despite a recent dose of painkiller)

The commonly used opioids available in oral and injectable formulations include the following:

• Morphine
• Morphine long-acting (Avinza, Kadian)
• Hydromorphone (Dilaudid)
• Oxycodone (Oxecta)
• Oxycodone long-acting (OxyContin)
• Hydrocodone (Vicodin, Lortab)
• Oxymorphone (Opana)
• Codeine
• Fentanyl
• Methadone
• Meperidine

Fentanyl is also available as transdermal patch and oral/nasal spray.

For moderate pain, hydrocodone or oxycodone may be used, along with an NSAID or acetaminophen, if required. For severe pain, high-potency opioids such as morphine, hydromorphone or fentanyl may be used.

Opioid medications

Following are the steps in rotation of opioid medications given via oral, IV, IM and SC administrations:

• Calculate daily dose of current opioid
• Determine the new opioid and route of administration based on the equianalgesic chart
• Calculate the equianalgesic dose for the new opioid
• Initiate new opioid with a lower than equianalgesic dose to account for cross-tolerance
• Titrate the new opioid based on patient’s pain response
• Achieve rapid analgesic effects in the first 24 hours
• Monitor effectiveness of analgesia, and the new opioid’s side effects
• Reassess analgesic effects every two or three days.
• Manage breakthrough pain with rapid-release short-acting opioid doses. Assess pain relief and adverse effects after 60 minutes.

Fentanyl transdermal patch

The steps for conversion to transdermal patch are as follows:

• Calculate current daily dose
• Calculate per-hour dose of fentanyl transdermal patch based on the equianalgesic chart
• Use patch with lower initial dose to allow for cross-tolerance
• Manage breakthrough pain with morphine as needed
• Titrate patch every 72 hours

Cautions relating to fentanyl transdermal patches include the following:

• Transdermal fentanyl is not suitable for breakthrough or unstable pain that requires frequent dosage adjustments.
• Transdermal patches are used only for opioid-tolerant patients and not for an opioid-naive patient.
• No external heat should be applied to the patch, because it may increase absorption and lead to overdose.

Fentanyl spray

Fentanyl oral or nasal spray is used for management of breakthrough cancer pain. Fentanyl sprays should not be used in opioid-naïve patients.

Opioids have a few side effects that may have to be managed with medications. Side effects of opioids include the following:

• Constipation
• Drowsiness
• Nausea and vomiting
• Urinary retention
• Impairment of psychomotor functions such as
  • Precise motor coordination skills
  • Cognitive problem solving
  • Attention
• Involuntary muscle jerking (myoclonus)

The primary risks with opioid medications are:

• Developing tolerance to opioids
• Addiction, especially when used over an extended period of time, which can lead to dangerous behavioral changes

Suddenly stopping the opioid may cause withdrawal symptoms such as:

• Diarrhea
• Nausea and vomiting
• Muscle pain
• Anxiety and irritability

Opioid overdose can lead to life-threatening conditions such as:

• Loss of consciousness
• Shallow breathing that may progress to complete respiratory failure
• Reduced heart rate