Variability in opioid equivalence calculations

Abstract

Objective. Equianalgesic conversion methods are commonly used to switch patients from one opioid to another due to suboptimal pain relief or adverse events. There is no universally accepted opioid conversion method, however, and there is often significant variability between conversion resources. As a result, patients are at risk for undertreated pain and serious adverse events. The purpose of this survey was to compare the equianalgesic conversion estimates between nurse practitioners, pharmacists, and physicians for commonly prescribed opioids. Methods. A survey form was developed using Survey Monkey. Participation was solicited by providing a link to the survey via social media (e.g., Facebook, Twitter, LinkedIn, etc.) and emailing professional organizations for sharing with their members and followers. Data collected included demographics and estimated morphine equivalents (MEQs) of hydrocodone 80 mg, fentanyl transdermal patches 1,800 mcg (as 75 mcg/hour), methadone 40 mg, oxycodone 120 mg, and hydromorphone 48 mg. Participants were also asked to provide their choice of reference utilized to complete the conversions, including personal knowledge. Descriptive analyses were performed using measures of central tendency. Hypothesis testing was performed using Pearson’s chi-squared and Fisher’s Exact Test for categorical data and the Kruskal–Wallis equality of populations rank test for continuous data to assess differences between median opioid doses by professional groups. Results. The total number of respondents included in the analysis was 319. Physicians, pharmacists, and nurse practitioners/physician assistants comprised 25.4%, 56.7%, and 16.3%, respectively, of respondents. The overall mean (6 standard deviation) MEQ doses for fentanyl, hydrocodone, hydromorphone, methadone, and oxycodone were: 176 (6117) mg, 88 (642) mg, 192 (655) mg, 193 (6201) mg, and 173 (639) mg, respectively. For fentanyl, the mean (6standard deviation) MEQ doses were 180 (6122) mg, 178 (6128) mg, and 157 (668) mg, for physicians, pharmacists, and nurse practitioners/ physician assistants, respectively. For all three groups of clinicians, the median MEQ dose for fentanyl was 150 mg. The mean (6standard deviation) MEQ doses of methadone for physicians, pharmacists, and nurse practitioners/physician assistants were: 214 (6142) mg, 171 (6107) mg, and 185 (6129) mg, respectively. The median MEQ dose for methadone was 160 mg for each of the clinician groups. Conclusions. As evidenced by large standard deviations, there was significant variation in mean opioid conversions to MEQ doses within each profession type, particularly for fentanyl and methadone. The median MEQ doses provided for opioid conversions were the same among each profession. No universal method exists that allows each of the five studied opioids to be accurately and consistently converted to another opioid (i.e., morphine).