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Factors associated with willingness to take extended release naltrexone among injection drug users Ahamad, Keith; Milloy, MJ; Nguyen, Paul; Uhlmann, Sasha; Johnson, Cheyenne; Korthuis, Todd P; Kerr, Thomas; Wood, Evan May 3, 2015

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RESEARCHFactors associated with wextended release naltrexonncern worldwide. Globally, opioids top the list of illicit clearly demonstrated significant reductions in these con-Ahamad et al. Addiction Science & Clinical Practice  (2015) 10:12 DOI 10.1186/s13722-015-0034-5treatment. Commonly reported barriers to programLaurel Street, Vancouver, BC V5Z 1M9, CanadaFull list of author information is available at the end of the articledrugs that cause substantial morbidity and mortality [1].In the United States alone, over 5 million people abusedprescription pain relievers in 2010 [2]. Nonmedical usersof prescription opioids have also been shown to be al-most 8 times more likely to use heroin and over 4 timesmore likely to use intravenously [3].sequences through medically assisted treatment withmethadone or buprenorphine, which are the gold stan-dards for medical management of opioid use disorder[4-7]. In terms of psychosocial treatments, past studieshave generally shown that without opioid-agonist medi-cations like methadone or buprenorphine, the vastmajority of patients will be treatment-refractory to psy-chosocial and nonpharmacological interventions [4,8].Unfortunately, due to the real or perceived side effectsor programmatic characteristics, treatment with metha-done and buprenorphine does not attract all users into* Correspondence: uhri-ew@cfenet.ubc.ca1British Columbia Centre for Excellence in HIV/AIDS, St. Paul’s Hospital, 1081Burrard Street, Vancouver, BC V6Z 1Y6, Canada3Department of Medicine, University of British Columbia, 10th Floor 2775Opioid use disorder remains a major public health con-Background: Although opioid-agonist therapy with methadone or buprenorphine/naloxone is currently the mainstayof medical treatment for opioid use disorder, these medications often are not well accepted or tolerated by patients.Recently, extended release naltrexone (XR-NTX), an opioid antagonist, has been advanced as an alternative treatment.The willingness of opioid-addicted patients to take XR-NTX has not been well described.Methods: Opioid-using persons enrolled in a community-recruited cohort in Vancouver, Canada, were asked whether ornot they would be willing to take XR-NTX. Logistic regression was used to independently identify factors associated withwillingness to take the medication.Results: Among the 657 participants surveyed between June 1, 2013, and November 30, 2013, 342 (52.1%) were willingto take XR-NTX. One factor positively associated with willingness was daily heroin injection (adjusted odds ratio [AOR] =1.53; 95% confidence interval [CI] = 1.02–2.31), whereas Caucasian ethnicity was negatively associated (AOR = 0.59; 95%CI = 0.43–0.82). Satisfaction with agonist therapy (13.4%) and unwillingness to stop opioids being used for pain (26.9%)were the most common reasons for being unwilling to take XR-NTX.Conclusions: A high level of willingness to take XR-NTX was observed in this setting. Interestingly, daily injectionheroin use was positively associated with willingness, whereas Caucasian participants were less willing to takeXR-NTX. Although explanations for unwillingness were described in this study, further research is needed toinvestigate real-world acceptability of XR-NTX as an additional option for the treatment of opioid use disorder.Keywords: Addiction, Willingness to take, Opioid antagonistBackground While the health and social consequences of opioiduse disorder are well documented, past studies havedrug usersKeith Ahamad1,2, MJ Milloy1, Paul Nguyen1, Sasha UhlmaThomas Kerr1 and Evan Wood1,3,6*Abstract© 2015 Ahamad et al.; licensee BioMed CentraCommons Attribution License (http://creativecreproduction in any medium, provided the orDedication waiver (http://creativecommons.orunless otherwise stated.Open Accessillingness to takene among injection1, Cheyenne Johnson1, Todd P Korthuis4,5,l. This is an Open Access article distributed under the terms of the Creativeommons.org/licenses/by/4.0), which permits unrestricted use, distribution, andiginal work is properly credited. The Creative Commons Public Domaing/publicdomain/zero/1.0/) applies to the data made available in this article,Ahamad et al. Addiction Science & Clinical Practice  (2015) 10:12 Page 2 of 6entry include limited treatment availability, the highthreshold of treatment programs (i.e., safe dose titrationtimelines), and requirements that opioid-agonist medica-tions must be provided via daily, witnessed ingestion [9].Furthermore, while they vary from setting to setting,retention rates with opioid-agonist treatments are onlyapproximately 60 percent, and many patients on metha-done or buprenorphine should remain on this medicationindefinitely [10-12]. Oral naltrexone, an opioid-receptorantagonist, has been proposed as an alternative for pa-tients. Naltrexone has several advantages in that it has fewdrug–drug interactions, no physical dependence, and a fa-vorable side-effect profile [13]. Unfortunately, due to therequirement for daily oral dosing, medication adherencehas been the major barrier to its efficacy [14].Recently, naltrexone for extended-release injectablesuspension (XR-NTX), which is administered via intra-muscular injection every 4 weeks, has been advanced asan alternative treatment [15,16]. Placebo-controlled trialshave demonstrated its efficacy in retaining patients intreatment, increasing abstinence, and decreasing opioidcravings [15-17]. However, it has recently been notedthat the willingness of opioid-addicted patients to takeXR-NTX has not been well described [18]. Since little isknown about the willingness of opioid-addicted patientsto take an extended-release, opioid-antagonist medica-tion (or about factors that may predict willingness), weundertook this study to examine the willingness to useXR-NTX among opioid-addicted patients participatingin a cohort study in Vancouver, Canada.MethodsData for this study were derived from the Vancouver Injec-tion Drug Users Study (VIDUS), an open, prospective co-hort of HIV-seronegative individuals who inject drugs, andthe AIDS Care Cohort to Evaluate Access to Survival Ser-vices (ACCESS), an open, prospective cohort of HIV-seropositive individuals who use illicit drugs in Vancouver,Canada. Detailed methodology has previously been de-scribed [19,20]. Participants were eligible for the study ifthey were 18 years or older, used illicit drugs other thancannabis within the past month, resided in the GreaterVancouver region, and provided informed consent. Partici-pants were recruited through extensive street-based out-reach methods and snowball sampling, beginning in May1996. At baseline and every 6 months thereafter, partici-pants completed an interviewer-administered question-naire that elicited information regarding sociodemographiccharacteristics, drug use, HIV risk behaviors, and treatmentutilization, and underwent an examination by a nurse. Par-ticipants received a $20 CAD stipend for each visit. VIDUSand ACCESS study recruitment and follow-up procedureswere essentially identical, with the exception of questionsspecific to HIV infection, to enable merged analyses. Boththe VIDUS and ACCESS studies were ethically approvedby the Research Ethics Board of Providence Health Care/University of British Columbia.For the primary analysis, we restricted the study sam-ple to those who reported any use of opioids or who en-rolled in methadone maintenance therapy in the past6 months, and assessed whether participants were will-ing to take XR-NTX for opioid addiction treatment byadding questions to follow-up visits between June 1,2013, and November 30, 2013. Specifically, participantswere asked: “There is a new medication that can begiven to people who have detoxed from heroin or otheropioids, including methadone. It is given by intramuscu-lar injection. It completely blocks the effects of opioids,including pain medications, for 30 days. If you are onmethadone or using other opioid drugs, would you beinterested in taking this medication if it becomes avail-able in Canada?” Since XR-NTX was not available inCanada at the time these questions were utilized, staffwere trained to answer questions about the medication’seffects, induction, and duration of action. Participantswho answered “Yes” were compared to those who an-swered “No” on a variety of a priori-selected sociodemo-graphic, behavioral, and drug use variables hypothesizedto be associated with willingness to take XR-NTX.These variables included: age (per year older); femalegender (yes vs. no); ethnicity (Caucasian vs. other); dailyheroin injection (yes vs. no); daily cocaine injection (yesvs. no); daily crack smoking (yes vs. no); homelessness(yes vs. no); involvement in sex work, defined as exchan-ging sex for money, gifts, food, shelter, clothes, drugs, orother commodities (yes vs. no); HIV seropositivity (yesvs. no); or participation in drug treatment, defined as al-cohol and/or drug treatment other than methadonetreatment (yes vs. no). All behavioral and drug use char-acteristics refer to the 6-month period prior to the inter-view. All variable definitions have been used extensivelyand were identical to earlier publications [21,22].We used bivariate and multivariate logistic regressionanalyses to determine factors associated with the willing-ness to take XR-NTX. To identify the independent cor-relates of willingness to take XR-NTX, only variablesthat were associated with willingness at p-value < 0.10 inbivariate analyses were considered in the full multivari-ate model. Using the backwards-selection procedure, weconstructed the final multivariate model with the bestfit, as indicated by the lowest Akaike Information Criter-ion (AIC) value.As a sub-analysis among participants who did not reportany willingness to take XR-NTX, their reasons from thesubsequent question were collated. Participants could se-lect more than one response from the following reasons:“Not using opioids”; “happy with methadone/suboxone(buprenorphine/naloxone)”; “don’t feel that I could detoxfrom opioid use or reduce my methadone to zero”; “feel Icould not get off my pain med”; “don’t want to take along-acting medication by injection”; and “other”. All stat-istical analyses were performed using SAS software ver-sion 9.3 (SAS, Cary, NC, USA). All statistical tests weretwo-sided, with alpha = 0.05.ResultsBetween June 1, 2013, and November 30, 2013, 657opioid-using VIDUS and ACCESS participants wereinterviewed and included in the present analysis. Amongthese individuals, median age was 48 (inter-quartilerange = 41–53); 249 (37.9%) were female; and 397(60.4%) were Caucasian (Table 1).Of the 657 participants, 342 (52.1%) indicated a will-ingness to take XR-NTX. As shown in Table 1, thesociodemographic, behavioral, and drug use character-istics associated with a willingness to take XR-NTX inunadjusted analyses included: age, female gender, dailyheroin injection, and Caucasian ethnicity (all p < 0.05).The results of the multivariate analysis are presented inTable 2. Factors independently associated with a will-ingness to take XR-NTX included: daily heroin injec-tion (adjusted odds ratio [AOR] = 1.53; 95% confidenceTable 1 Characteristics of study participants assessed for willingness to take an opioid antagonist (N = 657)Characteristic Willingness Odds ratio(95% CI£)p valueNo = 315 (%) Yes = 342 (%)Age [Median, (IQR¥)] 49 (41–54) 46 (40–51) 0.98 (0.96–1.00) 0.015GenderMale 209 (66.3) 199 (58.2)Female 106 (33.7) 143 (41.8) 1.42 (1.03–1.95) 0.032Caucasian ethnicityNo 102 (32.4) 158 (46.2)Yes 213 (67.6) 184 (53.8) 0.56 (0.41–0.77) < 0.001Daily heroin injection*No 268 (85.1) 270 (79.0)Yes 47 (14.9) 71 (20.8) 1.50 (1.00–2.25) 0.050Daily cocaine injection*No 289 (91.7) 319 (93.3)Yes 26 (8.3) 23 (6.7) 0.80 (0.45–1.44) 0.457Daily crack smoking*No 251 (79.7) 279 (81.6)Yes 64 (20.3) 63 (18.4) 0.89 (0.60–1.30) 0.538Homelessness*No 273 (86.7) 295 (86.3)Yes 42 (13.3) 46 (13.5) 1.01 (0.65–1.59) 0.953dinAhamad et al. Addiction Science & Clinical Practice  (2015) 10:12 Page 3 of 6Sex work*No 293 (93.0)Yes 22 (7.0)HIV positiveNo 189 (60.0)Yes 126 (40.0)Participation in drug treatment**No 257 (81.6)Yes 57 (18.1)NOTE: Percentages do not necessarily sum to 100% due to missing data or roun*Activities in last 6 months.**Defined as drug and/or alcohol treatment other than a methadone program.¥IQR = inter-quartile range.£CI = confidence interval.312 (91.2)30 (8.8) 1.28 (0.72–2.27) 0.397198 (57.9)144 (42.1) 1.09 (0.80–1.49) 0.584275 (80.4)64 (18.7) 1.05 (0.71–1.56) 0.812g error.interval [CI] = 1.02–2.31); and Caucasian ethnicity(AOR = 0.59; 95% CI = 0.43–0.82]).As shown in Figure 1, of the 315 (47.9%) participantswho indicated that they would not be willing to takeXR-NTX, 320 reasons were given for unwillingness andincluded: 53 (16.6%) reported that they were not activelytaking opioids; 43 (13.4%) were happy with methadone/suboxone (buprenorphine/naloxone); 25 (7.8%) didn’tfeel that they could detox from opioids; 86 (26.9%) didn’tfeel that they could get off pain medications; 7 (2.2%)didn’t want to take a long-acting medication by injec-(19.7%) reported a variety of other reasons that were notconsistent enough to be collapsed into categories. Dataare available from the corresponding author.DiscussionIn the present study, we found high rates of willingnessto take XR-NTX among a community-recruited cohortof opioid drug users. We also found that daily heroinuse was independently associated with a higher likeli-hood of willingness to take XR-NTX, whereas Caucasianparticipants were associated with a lower likelihood ofwillingness. Among the reasons reported for unwilling-ness to take XR-NTX: a) the perceived inability to stopopioid use for pain, and b) satisfaction with methadone/buprenorphine were the most frequently cited reasons.This is the first study, to our knowledge, to assess pa-tients’ interest in taking a long-acting opioid antagonistfor the treatment of opioid addiction. Rather thanpatient-related factors, past studies have examined howindividual and organizational variables can influencetreatment program attitudes towards use of medicationsfor the treatment of opioid addiction [23]. Fuller et al.(2005) surveyed outpatient substance abuse treatmentcenters and found that standalone substance abuseTable 2 Multivariate analysis of factors associated withthe willingness to take an opioid antagonist (N = 657)Characteristic Adjusted odds ratio 95% CI£ p valueDaily heroin injection*Yes vs. No 1.53 1.02–2.31 0.043Female genderYes vs. No 1.29 0.93–1.79 0.133Caucasian ethnicityYes vs. No 0.59 0.43–0.82 0.002£CI = confidence interval.*Activities in last 6 months.Ahamad et al. Addiction Science & Clinical Practice  (2015) 10:12 Page 4 of 6tion; 9 (2.8%) reported concern regarding untreated painif injured; 23 (7.2%) reported they liked using heroin; 11(3.4%) reported needing more information; and 63Figure 1 Reasons given by participants who indicated they would not beclinics were less likely to provide naltrexone [24]. Paststudies have also examined adoption of naltrexone inthe context of alcohol use disorder and found that onlywilling to take XR-NTX by percentage.Ahamad et al. Addiction Science & Clinical Practice  (2015) 10:12 Page 5 of 615 percent of alcohol treatment clinicians prescribe nal-trexone often [25]. In light of the dearth of informationregarding patient profiles that may be appropriate forXR-NTX, Ling et al. outlined some of the questions re-garding the role of XR-NTX in opioid dependence, in-cluding the fact that “no one seems to have figured outthat perhaps we should ask our patients whether theywould like to take [XR-NTX]” [18].Our findings show a high degree of willingness totake XR-NTX, particularly among high-intensity heroininjectors. These results show there is a subset of opioidusers who are willing to try alternatives to traditionalopioid-agonist therapy. This may represent the fact thatmethadone has very high penetrance in Vancouver, andthat those who have had a longstanding opportunity toengage in methadone treatment remain hesitant to takethis medication for programmatic reasons (e.g., dailywitness ingestion) and may be interested in an alterna-tive [26]. Importantly, Kerr et al. showed in 2005 thatopioid-injecting Aboriginal patients were less than halfas likely to use methadone maintenance than non-Aboriginal persons [26]. In this regard, it is noteworthythat the majority of individuals in the non-Caucasiancategory in the present study were Aboriginal. Whilepreliminary, our results suggest that there are likelyreasons for the unwillingness to take opioid-agonisttreatment that are more prevalent among Aboriginalpersons, whereas this population may be more open toalternatives, including XR-NTX [26]. This is an issuethat will require further study, potentially using qualitativeresearch methods to explore this question and to examinewillingness and unwillingness to take XR-NTX.This study has limitations. As our study sample wasgenerated through street-based recruitment methods, gen-eralizing our findings to other populations of injectiondrug users requires caution. However, it is noteworthy thatthe cohort demographics are similar to other local andinternational studies of drug users [27-30]. Secondly, asour outcome of interest was willingness to take XR-NTX,actual rates of willingness and successful induction ontoXR-NTX will need to be studied in clinical trials in real-world settings. In particular, all elements of the medica-tions’ benefits and side-effect profile could not be fullydescribed in the context of our study. In this regard, as-sessment of specific populations, including HIV-infectedindividuals, is the subject of ongoing investigation, as canbe seen with the National Institute on Drug Abuse(NIDA) Clinical Trials Network (CTN) 055 CHOICESstudy [31]. Finally, socially desirable responding is a con-cern in studies of marginalized populations [32]. Althoughinterviewers were trained to build trust and rapport withparticipants, and confidentiality was assured, it is possiblewe overestimated the percentage of individuals willing toparticipate as a result of this concern.In summary, the present study found high rates ofwillingness to take XR-NTX in this setting. Interestingly,daily injection heroin use was independently and posi-tively associated with willingness to take XR-NTX, whileCaucasian participants were negatively associated withthis choice, suggesting that sub-populations may benefitfrom this medication. Although patient-reported expla-nations for unwillingness were described in this study,including satisfaction with agonist therapy and concernsregarding stopping opioid-based pain medications, furtherresearch is needed to investigate real-world acceptabilityof XR-NTX as an additional option for the treatment ofopioid use disorder.Competing interestsThe authors declare that they have no competing interests.Authors’ contributionsKA interpreted analyses and wrote large portions of the manuscript. EWconceived the study, participated in its design and coordination, and helpeddraft the manuscript. PN conducted the statistical analyses and aided in theinterpretation of analyses. SU, MJM, CJ, TK, and PTK were involved in revisingthe manuscript. Each author has approved of the final version of thismanuscript.AcknowledgementsThe authors thank the study participants for their contributions to theresearch, as well as current and past researchers and staff. We wouldspecifically like to thank: Peter Vann, Kristie Starr, Deborah Graham, TriciaCollingham, Carmen Rock, Jennifer Matthews, Steve Kain, Benita Yip, andGuillaume Colley for their research and administrative assistance. The study issupported by research funds from the U.S. National Institutes of Health (NIH):VIDUS (R01DA011591) and ACCESS (R01DA021525). This research wasundertaken, in part, thanks to funding for a Tier 1 Canada Research Chair inInner City Medicine, which supports Dr. Evan Wood. Dr. Milloy is supportedin part by NIH. Dr. Korthuis’ and Dr. Wood’s participation was supported byNIDA CTN U10 DA015815.Author details1British Columbia Centre for Excellence in HIV/AIDS, St. Paul’s Hospital, 1081Burrard Street, Vancouver, BC V6Z 1Y6, Canada. 2Department of FamilyPractice, University of British Columbia, 5950 University Boulevard Street,Vancouver, BC V6T 1Z3, Canada. 3Department of Medicine, University ofBritish Columbia, 10th Floor 2775 Laurel Street, Vancouver, BC V5Z 1M9,Canada. 4Department of Medicine, Oregon Health and Science University,3181 SW Sam Jackson Park Rd, Portland, OR 97239, USA. 5Department ofPublic Health-Preventive Medicine, Oregon Health and Science University,3181 SW Sam Jackson Park Rd, Portland, OR 97239, USA. 6Division ofEpidemiology and Population Health, BC Centre for Excellence in HIV/AIDS,608-1081 Burrard Street, Vancouver, BC V6Z 1Y6, Canada.Received: 23 October 2014 Accepted: 23 April 2015References1. The United Nations Office on Drugs and Crime. World Drug Report 20142014. 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