SMR indicates skeletal muscle relaxant.
eTable 1. NAMCS Variable and Population of Analysis
eTable 2. Number of US Office Visits with a Skeletal Muscle Relaxant Prescription, 2005-2016
eTable 3. Office Visits With Newly Prescribed or Continued Opioid Therapy, 2016
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Soprano SE, Hennessy S, Bilker WB, Leonard CE. Assessment of Physician Prescribing of Muscle Relaxants in the United States, 2005-2016. JAMA Netw Open. 2020;3(6):e207664. doi:10.1001/jamanetworkopen.2020.7664
What trends characterize the outpatient prescribing of skeletal muscle relaxants in the United States?
In this cross-sectional study of US physician visits, skeletal muscle relaxant prescribing doubled between 2005 and 2016. This increase was associated primarily with an increase in office visits with continuing use of skeletal muscle relaxants. New use of skeletal muscle relaxants was stable. Skeletal muscle relaxants were prescribed disproportionately to older adults, a high-risk population in whom these medications are potentially inappropriate, and were often prescribed concomitantly with opioids despite guidelines warning against this potentially dangerous combination.
This evidence of increasing continuing use of skeletal muscle relaxants, their disproportionately high use in older adults, and their concomitant use with opioids all represent trends with potentially adverse clinical and public health consequences.
Little is known to date about national trends in the prescribing of skeletal muscle relaxants (SMRs), the use of which is associated with important safety concerns, especially in older adults and in those who use concomitant opioids.
To measure national trends in SMR prescribing over a 12-year period.
Design, Setting, and Participants
This cross-sectional study used data from the National Ambulatory Medical Care Survey from January 2005 to December 2016. Data were analyzed from August 21, 2018, to July 18, 2019. The study included patients with ambulatory care visits who had encounters with non–federally funded, office-based physicians in the United States.
SMR use, categorized as newly prescribed or continued therapy at the office visit.
Main Outcomes and Measures
Ambulatory care visits—overall and stratified by calendar year, geographic region, and patient age, sex, and race—in which an SMR was newly prescribed or continued were quantified. Among office visits in which an SMR was newly prescribed, diagnoses were assessed. Concomitant medications were quantified for all office visits, stratified by new or continued therapy. Survey visit weights were used to estimate nationally representative measures, and age-standardized rates were generated by geographic region using US Census data.
This study included a total of 314 970 308 office visits (mean [SD] age, 53.5 [15.2] years; 194 621 102 [61.8%] men and 120 349 206 [38.2%] women). In 2016, there were 30 730 262 (95% CI, 30 626 464-30 834 060) US ambulatory care visits in which an SMR was either newly prescribed or continued as ongoing therapy. Patients in these visits were most frequently female (58.2% [95% CI, 57.9%-58.6%]), white (53.7% [95% CI, 53.4%-54.0%]), and aged 45 to 64 years (48.5% [95% CI, 48.2%-48.9%]). During the study period, office visits with a prescribed SMR nearly doubled from 15.5 million (95% CI, 15.4-15.6 million) in 2005 to 30.7 million (95% CI, 30.6-30.8 million) in 2016. Although visits for new SMR prescriptions remained stable, office visits with continued SMR drug therapy tripled from 8.5 million (95% CI, 8.4-8.5 million) visits in 2005 to 24.7 million (95% CI, 24.6-24.8 million) visits in 2016. Older adults accounted for 22.2% (95% CI, 21.8%-22.6%) of visits with an SMR prescription. Concomitant use of an opioid was recorded in 67.2% (95% CI, 62.0%-72.5%) of all visits with a continuing SMR prescription.
Conclusions and Relevance
This study found that SMR use increased rapidly between 2005 and 2016, which is a concern given the prominent adverse effects and limited long-term efficacy data associated with their use. These findings suggest that approaches are needed to limit the long-term use of SMRs, especially in older adults, similar to approaches to limit long-term use of opioids and benzodiazepines.
In response to the opioid epidemic, clinicians and patients are increasingly seeking alternatives to opioids for the management of musculoskeletal conditions. Centrally acting skeletal muscle relaxants (SMRs), such as baclofen, carisoprodol, chlorzoxazone, cyclobenzaprine, metaxalone, methocarbamol, orphenadrine, and tizanidine, are labeled for acute musculoskeletal conditions including spasms and lower back pain; they are used off-label for neuropathic pain, chronic noncancer pain, temporomandibular disorder pain, and numerous nonpain conditions.1 A 2003 systematic review concluded that SMRs are effective for acute low back pain (although their comparative effectiveness vs analgesics or nonsteroidal anti-inflammatory drugs for acute low back pain is unknown), the evidence for chronic low back pain is less convincing, and SMRs must be used with caution because of central nervous system adverse effects, such as drowsiness and dizziness.2 Because of the lack of evidence regarding the long-term efficacy and safety of SMRs and the unquantified risk of abuse, dependence, and overdose,1,3 recommendations generally limit the use of SMRs to a maximum duration of 2 to 3 weeks.4 Despite such recommendations, a 1988-1994 study found that 44.5% of people taking SMRs were continuously treated for longer than 1 year.5 Carisoprodol, chlorzoxazone, cyclobenzaprine, methocarbamol, metaxalone, and orphenadrine are all considered potentially inappropriate medications in older adults,6,7 in whom these agents are associated with sedation, cognitive impairment, and fracture.8 An additional concern regarding the inappropriate use of SMRs is the potential for drug-drug interactions, particularly with opioids.9
We sought to characterize national trends in SMR prescribing, both overall and in older adults, and to examine the concomitant prescribing of SMRs with opioids. Therefore, we examined nationally representative data from the National Ambulatory Medical Care Survey (NAMCS) for the 12-year period spanning from 2005 to 2016.
We conducted a retrospective cross-sectional analysis of SMR prescribing using publicly available NAMCS data from January 2005 to December 2016. NAMCS is a US-based, annual survey of non–federally funded office-based physicians engaged in direct patient care.10 Survey data are collected from sampled health care professionals by trained proctors. Office visit records are weighted based on the most recently available census data to provide a nationally representative view of all ambulatory care visits in the United States. The survey captures information about the office visit, such as the reason for the encounter and diagnoses, medications, and demographic information about the patient, as well as information about the provider and their practice.
We identified all office visits in which an SMR was recorded as either newly prescribed or continued ongoing drug therapy, referred to herein as an SMR visit. To limit the data set to records of interest, we generated a list of Lexicon Plus (Cerner Multum Inc) drug identification codes for baclofen, carisoprodol, chlorzoxazone, cyclobenzaprine, metaxalone, methocarbamol, orphenadrine, and tizanidine. From these records, we extracted visit information, patient demographic characteristics, and record weights to generate national estimates. We examined the total number of visits per year; the race, ethnicity, and sex of the patient; and the region of the visit. Furthermore, we stratified counts by SMR agent and whether the SMR was newly prescribed or continued drug therapy.
We identified patients who were newly prescribed an SMR during the recorded visit by linking the new or continued status of reported medications (NCMed) variable to the SMR drug identification code. The NCMed variable indicates whether the medication was newly prescribed during the office visit or the patient was instructed to continue the medication as a part of their ongoing drug therapy. We examined the number of visits per year, the patient’s primary reason for the office visit, and all recorded diagnoses. All concomitant medications were examined for new SMR visits, and concomitant opioids were examined for continued SMR visits. A list of variables used, corresponding NAMCS variable names, and the population in which they were examined are presented in eTable 1 in the Supplement. For variables permitting multiple entries per visit, we included all entries without regard to ordering, eg, using all 5 diagnosis fields recorded in the 2016 survey.
We conducted analyses using the Statistical Package for Social Scientists, version 25 (IBM Corp) from August 21, 2018, to July 18, 2019. The University of Pennsylvania’s Office of Regulatory Affairs determined that this research did not require institutional review board oversight because the NAMCS is a publicly available data set. This article complies with the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline for cross-sectional studies.11
Patient demographic characteristics for SMR visits are shown in Table 1. The cross-sectional analysis included a total of 314 970 308 office visits (mean [SD] age, 53.5 [15.2] years; 194 621 102 [61.8%] men and 120 349 206 [38.2%] women). In 2016, there were 30 730 262 (95% CI, 30 626 464-30 834 060) US ambulatory care visits in which an SMR was either newly prescribed or continued as ongoing therapy. Patients prescribed an SMR in 2016 tended to be female (58.2% [95% CI, 57.9%-58.6%] women vs 41.8% [95% CI, 41.4%-42.1%] men). Racial demographic characteristics for SMR users in 2016 were as follows: 53.7% white (95% CI, 53.4%-54.0%), 10.2% African American (95% CI, 9.7%-10.6%), 1.2% Asian (95% CI, 1.0%-1.5%), and 2.2% Native American or Alaska Native (95% CI, 2.0%-2.5%). There were no data available for Native Hawaiians, and 1.5% (95% CI, 1.3%-1.8%) of patients had more than 1 race reported. As shown in eTable 2 in the Supplement and Figure 1, the number of US office visits in which an SMR was either newly prescribed or continued doubled from 15.5 million (95% CI, 15.4-15.6 million) visits in 2005 to 30.7 million (95% CI, 30.6-30.8 million) visits in 2016. During this 12-year period, the number of office visits resulting in new SMR prescriptions remained relatively stable at approximately 6 million (95% CI, 6.0-6.3 million) per year, whereas office visits for continued SMR drug therapy tripled from 8.5 million (95% CI, 8.4-8.5 million) to 24.7 million (95% CI, 24.6-24.8 million).
Adults older than 65 years accounted for 22.2% (95% CI, 21.9%-22.6%) of SMR visits in 2016, although this group accounted for just 14.5% of the US population.12 In 2016, the demographic characteristics of the other age groups were as follows: 0.3% (95% CI, 0.1%-0.5%) younger than 15 years, 4.1% (95% CI, 3.7%-4.4%) aged 15 to 24 years, 24.9% (95% CI, 24.6%-25.2%) aged 25 to 44 years, and 48.5% (95% CI, 48.2%-48.9%) aged 45 to 65 years. As shown in Figure 2, the proportion of visits that were SMR visits among patients 65 years and older increased 3-fold (from 1.3 SMR visits [95% CI, 1.0-1.7] per 100 office visits in 2005 to 4.3 SMR visits [95% CI, 4.1-4.6] per 100 office visits in 2016). The prescription of SMRs to older adults considered potentially inappropriate medications in this population (ie, carisoprodol, chlorzoxazone, cyclobenzaprine, metaxalone, methocarbamol, and orphenadrine) approximately doubled from 2.2 million (95% CI, 2.1-2.4 million) office visits in 2005 to 4.3 million (95% CI, 4.2-4.5 million) office visits in 2016.
The most common diagnoses between 2005 and 2015 reported for new SMR visits are shown in Table 2; the diagnosis coding system used for the NAMCS data shifted from the International Classification of Diseases, Ninth Revision, Clinical Modification to the International Classification of Diseases, Tenth Revision, Clinical Modification in 2016. The most common diagnoses during these visits were related to back pain and other musculoskeletal conditions; this pattern was maintained in 2016. As shown in Table 2, among new SMR visits, hydrocodone-acetaminophen was the most common concomitant therapy. Other analgesics, such as ibuprofen, naproxen, and tramadol, were also commonly used. As shown in eTable 3 in the Supplement, in 2016, 67.2% (95% CI, 62.0%-72.5%) of continuing SMR visits recorded concomitant therapy with an opioid, in contrast to 10.3% (95% CI, 9.8%-13.2%) of all ambulatory care visits nationally.
Table 3 shows the number of office visits and age-standardized rates of SMR visits for 2005 and 2016 stratified by geographic region and by new vs continued SMR. In the Northeast, age-standardized new SMR visit rates changed by −33.4% (95% CI, −31.7% to −36.4%), whereas continued SMR visit rates increased by 325.1% (95% CI, 320.2% to 342.4%). We observed a similar pattern in the South, with a −15.8% (95% CI, −15.2% to −17.0%) change in new SMR visits accompanied by a 79.1% (95% CI, 68.8% to 82.2%) increase in continued SMR visits. In the Midwest, new and continued SMR visit rates increased by 26.9% (95% CI, 22.1% to 28.9%) and 297.6% (95% CI, 273.8% to 307.5%), respectively. We observed similar but less marked increases in new and continued SMR visit rates in the West, with increases of 5.4% (95% CI, 3.8% to 5.6%) and 91.6% (95% CI, 87.4% to 93.2%), respectively.
This analysis of nationally representative office visit data found that SMR use doubled from 2005 to 2016 and that there was a disproportionately high use of these drugs in older adults, a population in which SMR use is potentially inappropriate. These increasing rates did not appear to have an association with the decline in opioid prescribing that began in 2012 in both the general ambulatory care population and in the older adult population.13 Furthermore, among visits with a continuing SMR, 67.2% of patients were concomitantly treated with an opioid—a combination that has the potential to cause serious drug-drug interactions, such as potentiated central nervous system depression and an increased risk of opioid overdose.9 As expected, among new users of SMRs, we found that the most common diagnoses were related to back pain and other musculoskeletal conditions. Interestingly, although the frequency of new initiation of SMR therapy remained stable, the number of office visits in which SMR therapy was continued tripled, indicating a potential shift in duration of use of these drugs. This trend is a concern given the limited evidence of long-term efficacy and the risk of serious central nervous system adverse effects and drug-drug interactions.
Although prior papers have examined the use of SMRs in veterans4 and older adults,14,15 the present study is, to our knowledge, the first study since 20045,16 to examine SMR use in the general population. The strengths of this study stem from the design of the NAMCS that permits us to make projections to US physician office visits.
This study has some limitations. The NAMCS does not capture patients leaving the hospital with an SMR prescription or allow researchers to follow patients over time or assess clinical outcomes. In addition, these data are limited to the United States, and we are unaware of recent analogous data from other countries.
Given their prominent adverse effects and the limited evidence for their long-term efficacy, growth in the continued use of SMRs, particularly in older adults and concomitantly with opioids, is concerning. Given the findings of this cross-sectional study, efforts to limit the long-term use of SMRs may be needed, especially for older adults, similar to efforts used to limit the long-term use of opioids17 and benzodiazepines.18
Accepted for Publication: April 7, 2020.
Published: June 24, 2020. doi:10.1001/jamanetworkopen.2020.7664
Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2020 Soprano SE et al. JAMA Network Open.
Corresponding Author: Charles E. Leonard, PharmD, MSCE, Department of Biostatistics, Epidemiology, and Informatics, Perelman School of Medicine, University of Pennsylvania, 807 Blockley Hall, 423 Guardian Dr, Philadelphia, PA 19104 (email@example.com).
Author Contributions: Ms Soprano had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Concept and design: Soprano, Hennessy, Leonard.
Acquisition, analysis, or interpretation of data: All authors.
Drafting of the manuscript: Soprano, Hennessy.
Critical revision of the manuscript for important intellectual content: Hennessy, Bilker, Leonard.
Statistical analysis: Soprano, Bilker.
Administrative, technical, or material support: Soprano, Leonard.
Supervision: Hennessy, Leonard.
Conflict of Interest Disclosures: Dr Leonard reported serving on the Executive Committee of the University of Pennsylvania's Center for Pharmacoepidemiology Research and Training. The Center receives funding for education from Pfizer. Dr Leonard reported receiving grants from the US National Institutes of Health, grants from the American Diabetes Association, nonfinancial support from John Wiley and Sons, and personal fees from the American College of Clinical Pharmacy and the University of Florida College of Pharmacy outside the submitted work. In addition, Dr Leonard reported that he is a special government employee of the US Food and Drug Administration. Dr Hennessy reported receiving grants from US National Institutes of Health during the conduct of the study. Dr Hennessy reported directing the University of Pennsylvania’s Center for Pharmacoepidemiology Research and Training, which receives educational funding from Pfizer, and he reported serving as a consultant for several pharmaceutical companies on unrelated matters. No other disclosures were reported.
Funding/Support: This research was supported by grant R01AG060975 (Dr Leonard) and grants R01AG025152, R01DA048001, and R01AG064589 (Dr Hennessy) from the US Department of Health and Human Services National Institutes of Health.
Role of the Funder/Sponsor: The funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.
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