Fentanyl is 100 times stronger than morphine.
Fentanyl is a powerful opioid with a strength 100 times that of morphine. Previous exposure to an opioid is considered an important safety requirement for patients about to use fentanyl.
Normally, a transdermal patch delivers fentanyl continuously over 3 days. Originally available in 25-, 50-, 75- and 100-μg/h patches, a 12-μg/h patch was introduced in 2006, mainly for dose adjustment rather than initial use.
The 25-µg/h fentanyl patch is recommended for people who have already used an opioid equivalent to 60 mg of morphine a day for a week or more.
From 1996-2015, 284 deaths linked with fentanyl patches were reported in Canada, many of them in the early stages of use.
The rise in both fentanyl use and adverse events related to it prompted Dr. Shawn Bugden, of the University of Manitoba in Canada, and coauthors to look at safety issues surrounding the patch.
They wanted to evaluate how the various warnings and safety bulletins regarding fentanyl prescription have impacted fentanyl-related risk and to assess the level of risk in the Manitoba population.
Inadequate prior exposure to opioids in at least half of cases
The team examined fentanyl patch prescriptions over a 12-year period, using data for 11,063 patients.
In 74% of cases, users' prior exposure to opioids was insufficient, and 18% of first-time patients started not with the recommended 25-µg/h dose, but with a dose of 50 µg/h or higher.
Prescription practices improved significantly during the 12-year period, as the rate of unsafe prescribing fell from 87% to 50%. Prescribing was safer in women and people under 65 years of age.
However, even by 2015, 15.7% of patients were receiving fentanyl patches without any exposure to opioids in the preceding 60 days, and half of all fentanyl patch prescriptions remained unsafe.
Patients aged 65 years and over experienced higher levels of unsafe fentanyl initiation than younger patients, exacerbated by the fact that absorption and metabolism alter with age.
Limitations to the study include the fact that it only looked at prescriptions obtained in Manitoba province. Nevertheless, previous studies in the US and Europe have yielded similar findings, implying that the results could be generalizable.
The researchers note:
"Considerable attention and effort have been placed into making prescribers aware of the need to ensure adequate opioid tolerance before prescribing fentanyl patches. Special attention should be paid to older patients, who are at greatest risk of adverse outcomes but had the lowest level of safe prescribing."
In a linked comment, Drs. Scott Lucyk and Lewis Nelson, of New York University, suggest that physician errors in prescribing fentanyl may stem from a lack of familiarity with the delivery system, and they call for more prescriber education to reduce the risks.
Prescribers can help to minimize the risk for patients, the report concludes, by making sure they have sufficient opioid tolerance before starting to use the fentanyl patch.
Medical News Today recently reported on a possible vaccine against fentanyl addiction.