RESEARCH REPORT
doi:10.1111/add.12834
A longitudinal comparison of retention in buprenorphine and methadone treatment for opioid dependence in New South Wales, Australia Lucy Burns1, Natasa Gisev1, Sarah Larney1,2, Timothy Dobbins3, Amy Gibson4, Jo Kimber1, Briony Larance1, Richard P. Mattick1, Tony Butler5,6 & Louisa Degenhardt1 National Drug and Alcohol Research Centre, University of NSW, Sydney, Australia,1 Alpert Medical School, Brown University, Providence, Rhode Island, USA,2 National Centre for Epidemiology and Population Health, Australian National University, Canberra, Australia,3 Centre for Health Research, University of Western Sydney, Sydney, Australia,4 Kirby Institute, University of NSW, Sydney, Australia5 and Australia School of Public Health and Community Medicine, University of NSW, Sydney, Australia6
ABSTRACT Background and Aims To examine characteristics of first-time methadone and buprenorphine clients and factors associated with risk of leaving first treatment in New South Wales (NSW), Australia. Design Retrospective linkage study of opioid substitution therapy (OST) treatment, court, custody and mortality data. Setting NSW, Australia. Participants First-time OST entrants (August 2001–December 2010). Measurements Characteristics of clients were examined. Time-dependent Cox models examined factors associated with the risk of leaving first treatment, with demographic, criminographic and treatment variables jointly considered. Interactions between medication and other variables upon risk of leaving treatment were examined. Findings There were 15 600 treatment entrants: 7183 (46%) commenced buprenorphine, 8417 (54%) commenced methadone; the proportion entering buprenorphine increased over time. Those starting buprenorphine switched medications more frequently and had more subsequent treatment episodes. Buprenorphine retention was also poorer. On average, 44% spent 3+ months in treatment compared with 70% of those commencing methadone; however, buprenorphine retention for first-time entrants improved over time, whereas methadone retention did not. Multivariable Cox models indicated that in addition to sex, age, treatment setting and criminographic variables, the risk of leaving a first treatment episode was greater on any given day for those receiving buprenorphine, and was dependent on the year treatment was initiated. There was no interaction between any demographic variables and medication received, suggesting no clear evidence of any particular groups for whom each medication might be better suited in terms of improving retention. Conclusions Although retention rates for buprenorphine treatment have improved in New South Wales, Australia, individuals starting methadone treatment still show higher retention rates. Keywords
Buprenorphine, methadone, opioid dependence, opioid substitution treatment, treatment retention.
Correspondence to: Lucy Burns, National Drug and Alcohol Research Centre, UNSWAustralia, Sydney, NSW 2052, Australia. E-mail: [email protected] Submitted 31 March 2014; initial review completed 13 June 2014; final version accepted 8 December 2014
INTRODUCTION Opioid substitution therapy (OST) is an effective treatment for opioid dependence. Several opioids have been demonstrated to be useful, including methadone [1–3] and buprenorphine [4]. Clinical trials have shown poorer retention for buprenorphine patients compared to those receiving methadone, attributed largely to inadequate dosage and discomfort in the induction phase [5]. In the largest cohort to date, work by our group compared retention rates in buprenorphine and methadone using © 2014 Society for the Study of Addiction
administrative data of all people in OST in New South Wales (NSW) from 2001 to 2006 [6]. In this analysis we found that, after controlling for age, sex and first administration point (i.e. whether a person started treatment in the community or prison), the hazard of leaving treatment on any given day was found to be 1.9 times higher for those on buprenorphine relative to those on methadone [6]. There has been no previous examination of patient-level or other variables that may be related to retention in either medication in real-world settings. Addiction, 110, 646–655
OST and treatment retention
NSW is the most populous state in Australia, with the largest OST programme in Australia. The NSW programme requires central approval for any dispensation of methadone or buprenorphine used to treat opioid dependence. Methadone has been prescribed since the 1970s; buprenorphine was introduced in 2001, and buprenorphine–naloxone in 2006. Patients may be prescribed OST medications in public or private clinics or through general practitioners; treatment is available in both community and prison settings. There is an emphasis upon supervised administration of medications to maximize medication and programmatic adherence [7,8]. The current study extends our previous work [6], providing the largest ecological comparison of buprenorphine and methadone, with data on every treatment episode for patients who first entered OST in NSW, Australia, between August 2001 and December 2010, with follow-up until March 2012. The aims were to: • compare characteristics of all new entrants to methadone and buprenorphine, including demographic and criminographic characteristics; • examine the dynamics of treatment engagement by these clients, including changing of medications prescribed and the settings in which medications were received (in prison or the community); and • examine factors associated with leaving the first episode of OST treatment, including the medication prescribed, treatment setting, demographic and criminographic characteristics and potential interactions of these with medication type. METHODS Sample The current study examined de-identified unit record data from all people commencing an OST treatment episode for the first time between 1 August 2001 (the date which buprenorphine was first subsidized on the Pharmaceutical Benefits Scheme in Australia) and 31 December 2010, with follow-up data until 31 March 2012. Data sources This study used three fully identified NSW and national administrative data sets that record information regarding OST, involvement in the criminal justice system and mortality. The data sets were linked by the data custodians and the researchers received only non-identifiable data. Opioid substitution treatment The Pharmaceutical Drugs of Addiction System (PHDAS) is a database of all methadone and buprenorphine recipients © 2014 Society for the Study of Addiction
647
in NSW, Australia since 1985. The PHDAS records each patient’s full name, date of birth, sex and postcode of residence. As proof of patient identity is required to be shown to the prescribing doctor before a prescription can be issued, the name and date of birth variables are of high accuracy in this data set. The PHDAS records patient admissions and exits from the treatment programme, and the medication dispensed. The PHDAS does not differentiate between buprenorphine and buprenorphine–naloxone combinations. In the PHDAS the prescriber must submit an application to prescribe methadone or buprenorphine to a particular client to the NSW Director-General of Health, when they wish to switch the medication the client is receiving, or if the prescribing doctor changes. A person may therefore have multiple changes within a given treatment episode, with changes in the medications prescribed, the person prescribing them and the setting in which treatment is delivered (prison versus the community). In this study, we defined an episode of continuous treatment in OST as one with no more than a 6-day break between treatment episodes. Where a gap of 7 days or greater occurred between an exit date and a start date for a new programme, a new episode of treatment was defined. Records for clients were excluded from all analyses if they were on a temporary programme (usually temporary interstate transfers), part of a clinical trial, were recorded as not having commenced their programme in the ‘reason for leaving’ field in the database or were recorded as completing their programme on the same day they were supposed to commence. There were also a small number of cases (n = 40) where an exit date was recorded prior to an entry date, and these cases were removed from the analyses. Variables examined from the PHDAS were: age, sex, type of treatment (methadone or buprenorphine), treatment setting (community pharmacy or custodial setting), date of commencement of a treatment episode, date and reason for leaving a treatment episode and dates of subsequent entries and exits. Offending and incarceration The Reoffending Database (ROD) is a data set maintained by the NSW Bureau of Crime Statistics and Research (BOCSAR), and contains records of all finalized court appearances in the Local, District and Supreme Courts of NSW since 1994. The ROD also contains incarceration records from the NSW Department of Corrective Services from 2000. In the current study, the ROD was used to determine when OST was commenced/administered in custody, as well as to ascertain baseline criminographic characteristics of treatment entrants. Addiction, 110, 646–655
648
L. Burns et al.
Mortality The National Death Index (NDI) is a database held by the Australian Institute of Health and Welfare (AIHW) and contains mortality data collected from each Australian State or Territory Registry of Births, Deaths and Marriages. Causes of death recorded in the NDI are determined by expert clinical coders at the Australian Bureau of Statistics on the basis of information contained in death certificates and, where available, coronial files. Dates of death were available for all deaths occurring between 2000 and March 2012. Death data were used to censor records in the survival analysis.
Cox proportional hazards models were used to evaluate the unadjusted and adjusted risk (hazards ratio: HR) and 95% CIs for leaving a first treatment episode. Time in treatment was evaluated in a time-dependent manner. All variables were entered into the overall adjusted model. The proportionality assumption was evaluated for all variables in the final model using the ln(time) interaction with each of the predictors. Significance for the proportionality assumption was determined at the P < 0.01 level, and those variables not meeting the proportionality assumption were included in the model with their ln(time) interaction with the time-varying predictor.
Data analysis
Ethics
All analyses were undertaken using SAS Enterprise Guide version 5.1 (SAS Institute Inc., Cary, NC, USA). Demographic and treatment characteristics of individuals commencing their first treatment episode were compared according to the type of OST first received (methadone or buprenorphine) using odds ratios (ORs) and 95% confidence intervals (CIs). In addition, criminographic variables were compared according to the form of OST first received and the setting in which treatment was initiated (in the community or custody). For each treatment setting, ORs were used to compare characteristics of people initiating methadone or buprenorphine for all categorical variables. The Mann–Whitney Wilcoxon test was used for comparisons of continuous variables. Statistical significance was established at the 0.05 level.
Support for this study was obtained from all data custodians (Pharmaceutical Services Unit, NSW Health, BOCSAR and AIHW). Ethical approval was obtained from the University of New South Wales, NSW Health’s Population and Health Services Research Ethics Committee, AIHW, the Alfred Hospital, Corrective Services NSW, Justice Health and Forensic Mental Health Network (NSW Health), the Aboriginal Health and Medical Research Council (AHMRC) and the Department of Justice Health Research Ethics Committee (Victoria).
Treatment retention The treatment end date was the end date of the programme or the date of death, whichever occurred first. Individuals without a treatment end date were assumed to still be in treatment at the end of follow-up (31 March 2012). The National Death Index database was used to extract information about date of death for individuals in the cohort. Cases where the date of death preceded the programme start date were deleted (n = 35 people). Individuals were censored in the analyses if they were still in treatment, had died, if the reason for leaving treatment was due to the client transferring out of NSW and, although rare, those who were recorded as having ‘successfully completed the OST programme’. Data about custody episodes were used to identify individuals who commenced or received OST in custody and the type of OST that was received. Criminal offences were coded according to the Australian and New Zealand Standard Offence Classification (ANZSOC) [9], and property, violent and drug offence categories were defined by BOCSAR in its standard crime statistic reporting [see for example, 10]. © 2014 Society for the Study of Addiction
RESULTS Characteristics of the cohort Between August 2001 and December 2010 there were a total of 15 600 new entrants into OST in NSW, 54% of whom commenced methadone and 46% buprenorphine. The median age at treatment entry increased over this time-period for both males and females (males: 27.4– 30.2; females: 25.4–30.0). Table 1 shows the demographic characteristics of these new entrants by treatment type. Males were more likely to enter both forms of treatment, comprising approximately 70% of all new entrants to both methadone and buprenorphine (OR = 1.08, 95% CI = 1.01–1.16). At first treatment entry, 48% of those commencing methadone and 51% commencing buprenorphine were aged 20–29 years; those whose first medication on entry was methadone were older than those first prescribed buprenorphine. People identified as being of Aboriginal and/or Torres Strait Islander descent were much more likely to first start treatment with methadone (OR = 2.58, 95% CI = 2.37–2.80). Buprenorphine made up a larger proportion of new treatment medications in more recent years. Individuals initiated on buprenorphine were more likely to start treatment in the community (97% on buprenorphine versus 67% commencing methadone) Addiction, 110, 646–655
OST and treatment retention
649
Table 1 Demographic and treatment characteristics of individuals starting their first treatment episode, according to medication type taken on entry to treatment (n = 15 600). Methadone (n = 8417)
Male Indigenous Age group* ≥40 years 30–39 years 20–29 years 10
68.3 0–114 18.3 31.2 35.1 31.5 75.8 21.8 2.0 0.4
4284 1231 112 22
%
3860 3 1035 1765 1985 1779
n
Methadone (n = 5649)
5281 1478 138 38
4539 2 1315 1973 2165 2018
n
76.2 21.3 2.0 0.6
65.5 0–111 19.0 28.5 31.2 29.1
%
Buprenorphine (n = 6935)
Initiated in the community (n = 12 584)
0.94–1.12 0.78–1.29 0.42–1.21
0.96 1.14 1.19 1.12 Ref. 1.03 1.00 0.71
95% CI
1.06–1.23 P < 0.001 0.88–1.05 1.06–1.23 1.11–1.29 1.04–1.21
1.14
Odds ratio (ref: B)
589 1557 440 182
2702 25 1354 2201 2173 1557
n
21.3 56.3 15.9 6.6
97.6 0–304 48.9 79.5 78.5 56.3
%
Methadone (n = 2768)
Initiated in custody (n = 3016)
56 147 29 16
240 24 103 166 195 147
n
22.6 59.3 11.7 6.5
96.8 0–106 41.5 66.9 78.6 59.3
%
Buprenorphine (n = 248)
Table 2 Criminographic characteristics of individuals starting their first treatment episode by medication type and treatment setting on first entry into treatment (n = 15 600).
Ref. 1.01 1.44 1.08
1.35 1.92 0.99 0.88
1.37
95% CI
0.73–1.39 0.91–2.30 0.61–1.93
0.65–2.88 P = 0.057 1.04–1.75 1.45–2.54 0.72–1.36 0.68–1.15
Odds ratio (ref: B)
650 L. Burns et al.
Addiction, 110, 646–655
OST and treatment retention
(a) Number of episodes
(b) Switching medications within a treatment episode
651
predictors of leaving treatment (Table 3). With respect to criminographic variables, those with more custody episodes (AHR = 1.39, 95% CI = 1.18–1.64 for >10 episodes), more offences (AHR = 0.99, 95% CI = 0.99–0.99) and a history of violent offending prior to entry into treatment (AHR = 1.14, 95% CI = 1.08–1.20) were at greater risk of leaving treatment. However, the significant interaction between time and number of previous offences indicates that this risk was not consistent over time. There was no interaction between medication type and any variable with the exception of calendar year, whereby people entering buprenorphine in more recent years had comparatively better retention compared with methadone (results of five additional Cox models which are stratified by the five first treatment year categories are available on request; these showed that all other predictors remained consistently associated with retention across calendar year). DISCUSSION
Figure 2 Subsequent number of episodes and switching of medications within an episode by first medication type for those who first entered treatment between 2001 and 2010. (a) Number of episodes; (b) switching medications within a treatment episode
when there was a decrease at 6, 9 and 12 months (Fig. 3). Similarly, for new entrants to methadone, a drop was observed at 6, 9 and 12 months in 2010 (Fig. 3). Whereas the proportion of new entrants remaining in buprenorphine treatment for 12 months increased by 10% (2001–10), this was not the case for methadone, where a 3% decrease was noted during the same time-frame. Several variables significantly predicted leaving the first treatment episode in the Cox proportional hazard model (Table 3). After controlling for covariates, being male [adjusted hazards ratio (AHR) = 1.13, 95% CI = 1.08–1.18], Indigenous (AHR = 1.22, 95% CI = 1.16–1.29) and younger (AHR = 1.89, 95% CI = 1.71–2.08 for those aged
doi:10.1111/add.12834
A longitudinal comparison of retention in buprenorphine and methadone treatment for opioid dependence in New South Wales, Australia Lucy Burns1, Natasa Gisev1, Sarah Larney1,2, Timothy Dobbins3, Amy Gibson4, Jo Kimber1, Briony Larance1, Richard P. Mattick1, Tony Butler5,6 & Louisa Degenhardt1 National Drug and Alcohol Research Centre, University of NSW, Sydney, Australia,1 Alpert Medical School, Brown University, Providence, Rhode Island, USA,2 National Centre for Epidemiology and Population Health, Australian National University, Canberra, Australia,3 Centre for Health Research, University of Western Sydney, Sydney, Australia,4 Kirby Institute, University of NSW, Sydney, Australia5 and Australia School of Public Health and Community Medicine, University of NSW, Sydney, Australia6
ABSTRACT Background and Aims To examine characteristics of first-time methadone and buprenorphine clients and factors associated with risk of leaving first treatment in New South Wales (NSW), Australia. Design Retrospective linkage study of opioid substitution therapy (OST) treatment, court, custody and mortality data. Setting NSW, Australia. Participants First-time OST entrants (August 2001–December 2010). Measurements Characteristics of clients were examined. Time-dependent Cox models examined factors associated with the risk of leaving first treatment, with demographic, criminographic and treatment variables jointly considered. Interactions between medication and other variables upon risk of leaving treatment were examined. Findings There were 15 600 treatment entrants: 7183 (46%) commenced buprenorphine, 8417 (54%) commenced methadone; the proportion entering buprenorphine increased over time. Those starting buprenorphine switched medications more frequently and had more subsequent treatment episodes. Buprenorphine retention was also poorer. On average, 44% spent 3+ months in treatment compared with 70% of those commencing methadone; however, buprenorphine retention for first-time entrants improved over time, whereas methadone retention did not. Multivariable Cox models indicated that in addition to sex, age, treatment setting and criminographic variables, the risk of leaving a first treatment episode was greater on any given day for those receiving buprenorphine, and was dependent on the year treatment was initiated. There was no interaction between any demographic variables and medication received, suggesting no clear evidence of any particular groups for whom each medication might be better suited in terms of improving retention. Conclusions Although retention rates for buprenorphine treatment have improved in New South Wales, Australia, individuals starting methadone treatment still show higher retention rates. Keywords
Buprenorphine, methadone, opioid dependence, opioid substitution treatment, treatment retention.
Correspondence to: Lucy Burns, National Drug and Alcohol Research Centre, UNSWAustralia, Sydney, NSW 2052, Australia. E-mail: [email protected] Submitted 31 March 2014; initial review completed 13 June 2014; final version accepted 8 December 2014
INTRODUCTION Opioid substitution therapy (OST) is an effective treatment for opioid dependence. Several opioids have been demonstrated to be useful, including methadone [1–3] and buprenorphine [4]. Clinical trials have shown poorer retention for buprenorphine patients compared to those receiving methadone, attributed largely to inadequate dosage and discomfort in the induction phase [5]. In the largest cohort to date, work by our group compared retention rates in buprenorphine and methadone using © 2014 Society for the Study of Addiction
administrative data of all people in OST in New South Wales (NSW) from 2001 to 2006 [6]. In this analysis we found that, after controlling for age, sex and first administration point (i.e. whether a person started treatment in the community or prison), the hazard of leaving treatment on any given day was found to be 1.9 times higher for those on buprenorphine relative to those on methadone [6]. There has been no previous examination of patient-level or other variables that may be related to retention in either medication in real-world settings. Addiction, 110, 646–655
OST and treatment retention
NSW is the most populous state in Australia, with the largest OST programme in Australia. The NSW programme requires central approval for any dispensation of methadone or buprenorphine used to treat opioid dependence. Methadone has been prescribed since the 1970s; buprenorphine was introduced in 2001, and buprenorphine–naloxone in 2006. Patients may be prescribed OST medications in public or private clinics or through general practitioners; treatment is available in both community and prison settings. There is an emphasis upon supervised administration of medications to maximize medication and programmatic adherence [7,8]. The current study extends our previous work [6], providing the largest ecological comparison of buprenorphine and methadone, with data on every treatment episode for patients who first entered OST in NSW, Australia, between August 2001 and December 2010, with follow-up until March 2012. The aims were to: • compare characteristics of all new entrants to methadone and buprenorphine, including demographic and criminographic characteristics; • examine the dynamics of treatment engagement by these clients, including changing of medications prescribed and the settings in which medications were received (in prison or the community); and • examine factors associated with leaving the first episode of OST treatment, including the medication prescribed, treatment setting, demographic and criminographic characteristics and potential interactions of these with medication type. METHODS Sample The current study examined de-identified unit record data from all people commencing an OST treatment episode for the first time between 1 August 2001 (the date which buprenorphine was first subsidized on the Pharmaceutical Benefits Scheme in Australia) and 31 December 2010, with follow-up data until 31 March 2012. Data sources This study used three fully identified NSW and national administrative data sets that record information regarding OST, involvement in the criminal justice system and mortality. The data sets were linked by the data custodians and the researchers received only non-identifiable data. Opioid substitution treatment The Pharmaceutical Drugs of Addiction System (PHDAS) is a database of all methadone and buprenorphine recipients © 2014 Society for the Study of Addiction
647
in NSW, Australia since 1985. The PHDAS records each patient’s full name, date of birth, sex and postcode of residence. As proof of patient identity is required to be shown to the prescribing doctor before a prescription can be issued, the name and date of birth variables are of high accuracy in this data set. The PHDAS records patient admissions and exits from the treatment programme, and the medication dispensed. The PHDAS does not differentiate between buprenorphine and buprenorphine–naloxone combinations. In the PHDAS the prescriber must submit an application to prescribe methadone or buprenorphine to a particular client to the NSW Director-General of Health, when they wish to switch the medication the client is receiving, or if the prescribing doctor changes. A person may therefore have multiple changes within a given treatment episode, with changes in the medications prescribed, the person prescribing them and the setting in which treatment is delivered (prison versus the community). In this study, we defined an episode of continuous treatment in OST as one with no more than a 6-day break between treatment episodes. Where a gap of 7 days or greater occurred between an exit date and a start date for a new programme, a new episode of treatment was defined. Records for clients were excluded from all analyses if they were on a temporary programme (usually temporary interstate transfers), part of a clinical trial, were recorded as not having commenced their programme in the ‘reason for leaving’ field in the database or were recorded as completing their programme on the same day they were supposed to commence. There were also a small number of cases (n = 40) where an exit date was recorded prior to an entry date, and these cases were removed from the analyses. Variables examined from the PHDAS were: age, sex, type of treatment (methadone or buprenorphine), treatment setting (community pharmacy or custodial setting), date of commencement of a treatment episode, date and reason for leaving a treatment episode and dates of subsequent entries and exits. Offending and incarceration The Reoffending Database (ROD) is a data set maintained by the NSW Bureau of Crime Statistics and Research (BOCSAR), and contains records of all finalized court appearances in the Local, District and Supreme Courts of NSW since 1994. The ROD also contains incarceration records from the NSW Department of Corrective Services from 2000. In the current study, the ROD was used to determine when OST was commenced/administered in custody, as well as to ascertain baseline criminographic characteristics of treatment entrants. Addiction, 110, 646–655
648
L. Burns et al.
Mortality The National Death Index (NDI) is a database held by the Australian Institute of Health and Welfare (AIHW) and contains mortality data collected from each Australian State or Territory Registry of Births, Deaths and Marriages. Causes of death recorded in the NDI are determined by expert clinical coders at the Australian Bureau of Statistics on the basis of information contained in death certificates and, where available, coronial files. Dates of death were available for all deaths occurring between 2000 and March 2012. Death data were used to censor records in the survival analysis.
Cox proportional hazards models were used to evaluate the unadjusted and adjusted risk (hazards ratio: HR) and 95% CIs for leaving a first treatment episode. Time in treatment was evaluated in a time-dependent manner. All variables were entered into the overall adjusted model. The proportionality assumption was evaluated for all variables in the final model using the ln(time) interaction with each of the predictors. Significance for the proportionality assumption was determined at the P < 0.01 level, and those variables not meeting the proportionality assumption were included in the model with their ln(time) interaction with the time-varying predictor.
Data analysis
Ethics
All analyses were undertaken using SAS Enterprise Guide version 5.1 (SAS Institute Inc., Cary, NC, USA). Demographic and treatment characteristics of individuals commencing their first treatment episode were compared according to the type of OST first received (methadone or buprenorphine) using odds ratios (ORs) and 95% confidence intervals (CIs). In addition, criminographic variables were compared according to the form of OST first received and the setting in which treatment was initiated (in the community or custody). For each treatment setting, ORs were used to compare characteristics of people initiating methadone or buprenorphine for all categorical variables. The Mann–Whitney Wilcoxon test was used for comparisons of continuous variables. Statistical significance was established at the 0.05 level.
Support for this study was obtained from all data custodians (Pharmaceutical Services Unit, NSW Health, BOCSAR and AIHW). Ethical approval was obtained from the University of New South Wales, NSW Health’s Population and Health Services Research Ethics Committee, AIHW, the Alfred Hospital, Corrective Services NSW, Justice Health and Forensic Mental Health Network (NSW Health), the Aboriginal Health and Medical Research Council (AHMRC) and the Department of Justice Health Research Ethics Committee (Victoria).
Treatment retention The treatment end date was the end date of the programme or the date of death, whichever occurred first. Individuals without a treatment end date were assumed to still be in treatment at the end of follow-up (31 March 2012). The National Death Index database was used to extract information about date of death for individuals in the cohort. Cases where the date of death preceded the programme start date were deleted (n = 35 people). Individuals were censored in the analyses if they were still in treatment, had died, if the reason for leaving treatment was due to the client transferring out of NSW and, although rare, those who were recorded as having ‘successfully completed the OST programme’. Data about custody episodes were used to identify individuals who commenced or received OST in custody and the type of OST that was received. Criminal offences were coded according to the Australian and New Zealand Standard Offence Classification (ANZSOC) [9], and property, violent and drug offence categories were defined by BOCSAR in its standard crime statistic reporting [see for example, 10]. © 2014 Society for the Study of Addiction
RESULTS Characteristics of the cohort Between August 2001 and December 2010 there were a total of 15 600 new entrants into OST in NSW, 54% of whom commenced methadone and 46% buprenorphine. The median age at treatment entry increased over this time-period for both males and females (males: 27.4– 30.2; females: 25.4–30.0). Table 1 shows the demographic characteristics of these new entrants by treatment type. Males were more likely to enter both forms of treatment, comprising approximately 70% of all new entrants to both methadone and buprenorphine (OR = 1.08, 95% CI = 1.01–1.16). At first treatment entry, 48% of those commencing methadone and 51% commencing buprenorphine were aged 20–29 years; those whose first medication on entry was methadone were older than those first prescribed buprenorphine. People identified as being of Aboriginal and/or Torres Strait Islander descent were much more likely to first start treatment with methadone (OR = 2.58, 95% CI = 2.37–2.80). Buprenorphine made up a larger proportion of new treatment medications in more recent years. Individuals initiated on buprenorphine were more likely to start treatment in the community (97% on buprenorphine versus 67% commencing methadone) Addiction, 110, 646–655
OST and treatment retention
649
Table 1 Demographic and treatment characteristics of individuals starting their first treatment episode, according to medication type taken on entry to treatment (n = 15 600). Methadone (n = 8417)
Male Indigenous Age group* ≥40 years 30–39 years 20–29 years 10
68.3 0–114 18.3 31.2 35.1 31.5 75.8 21.8 2.0 0.4
4284 1231 112 22
%
3860 3 1035 1765 1985 1779
n
Methadone (n = 5649)
5281 1478 138 38
4539 2 1315 1973 2165 2018
n
76.2 21.3 2.0 0.6
65.5 0–111 19.0 28.5 31.2 29.1
%
Buprenorphine (n = 6935)
Initiated in the community (n = 12 584)
0.94–1.12 0.78–1.29 0.42–1.21
0.96 1.14 1.19 1.12 Ref. 1.03 1.00 0.71
95% CI
1.06–1.23 P < 0.001 0.88–1.05 1.06–1.23 1.11–1.29 1.04–1.21
1.14
Odds ratio (ref: B)
589 1557 440 182
2702 25 1354 2201 2173 1557
n
21.3 56.3 15.9 6.6
97.6 0–304 48.9 79.5 78.5 56.3
%
Methadone (n = 2768)
Initiated in custody (n = 3016)
56 147 29 16
240 24 103 166 195 147
n
22.6 59.3 11.7 6.5
96.8 0–106 41.5 66.9 78.6 59.3
%
Buprenorphine (n = 248)
Table 2 Criminographic characteristics of individuals starting their first treatment episode by medication type and treatment setting on first entry into treatment (n = 15 600).
Ref. 1.01 1.44 1.08
1.35 1.92 0.99 0.88
1.37
95% CI
0.73–1.39 0.91–2.30 0.61–1.93
0.65–2.88 P = 0.057 1.04–1.75 1.45–2.54 0.72–1.36 0.68–1.15
Odds ratio (ref: B)
650 L. Burns et al.
Addiction, 110, 646–655
OST and treatment retention
(a) Number of episodes
(b) Switching medications within a treatment episode
651
predictors of leaving treatment (Table 3). With respect to criminographic variables, those with more custody episodes (AHR = 1.39, 95% CI = 1.18–1.64 for >10 episodes), more offences (AHR = 0.99, 95% CI = 0.99–0.99) and a history of violent offending prior to entry into treatment (AHR = 1.14, 95% CI = 1.08–1.20) were at greater risk of leaving treatment. However, the significant interaction between time and number of previous offences indicates that this risk was not consistent over time. There was no interaction between medication type and any variable with the exception of calendar year, whereby people entering buprenorphine in more recent years had comparatively better retention compared with methadone (results of five additional Cox models which are stratified by the five first treatment year categories are available on request; these showed that all other predictors remained consistently associated with retention across calendar year). DISCUSSION
Figure 2 Subsequent number of episodes and switching of medications within an episode by first medication type for those who first entered treatment between 2001 and 2010. (a) Number of episodes; (b) switching medications within a treatment episode
when there was a decrease at 6, 9 and 12 months (Fig. 3). Similarly, for new entrants to methadone, a drop was observed at 6, 9 and 12 months in 2010 (Fig. 3). Whereas the proportion of new entrants remaining in buprenorphine treatment for 12 months increased by 10% (2001–10), this was not the case for methadone, where a 3% decrease was noted during the same time-frame. Several variables significantly predicted leaving the first treatment episode in the Cox proportional hazard model (Table 3). After controlling for covariates, being male [adjusted hazards ratio (AHR) = 1.13, 95% CI = 1.08–1.18], Indigenous (AHR = 1.22, 95% CI = 1.16–1.29) and younger (AHR = 1.89, 95% CI = 1.71–2.08 for those aged
