Using mathematical modelling to extrapolate results from the North American Opiate Medication Initiative, we found that diacetylmorphine may be more effective and less costly than methadone maintenance treatment for chronic, refractory opioid dependence. The baseline model indicated that diacetylmorphine would decrease societal costs, largely by reducing costs associated with crime, and would increase both the duration and quality of life of treatment recipients. Because opioid users commit less crime and have lower rates of health care use and death while in treatment,7,51,52
the benefits in cost and health utility attributable to diacetylmorphine stemmed chiefly from its capacity to retain patients in treatment for longer periods than with methadone maintenance treatment.
From a societal perspective, diacetylmorphine was estimated to be cost-effective for a wide range of values of societal willingness to pay. We also presented the narrower perspective of the Ministry of Health (exclusion of costs related to criminal activity and out-of-pocket costs). However, decision-making based only on this perspective is akin to a silo-based approach to allocating government funds and is biased against health innovations that provide benefits beyond the scope of the health care system.
Our results on the cost-effectiveness of diacetylmorphine are consistent with those of an economic analysis based on data from two Dutch heroin-assisted treatment trials,21
despite differences in the design of the Dutch trials and the North American Opiate Medication Initiative, and the time horizon and analytic design of the economic analyses.
The Dutch trials compared methadone maintenance treatment with a combination of methadone and diacetylmorphine (prescribed concurrently), which changed the profiles of health utility and health resource use. Furthermore, participants in the Dutch trials were recruited from methadone maintenance programs, whereas participants in the North American Opiate Medication Initiative had to have been out of treatment for at least six months before trial entry. We considered a range of time horizons, using external parameters where necessary to extrapolate results to longer time horizons. The other economic analysis used trial data exclusively and focused only on a 12-month study period. The consistency in results between our analysis and the analysis of the Dutch trials appears to be due primarily to the advantages diacetylmorphine provides in retaining individuals in treatment.
We believe a lifetime horizon is the most appropriate period for evaluating treatments of chronic, recurrent diseases such as opioid dependence, because treatment is available indefinitely in practice and will have a long-term impact. The key outcomes, such as progressing to a drug-free state or death, would likely not be realized within the 12-month period of the North American Opiate Medication Initiative.
Our study was not without limitations. First, data on opioid users reaching state of abstinence were scarce, as were data on the long-term patterns of treatment and relapse among those receiving diacetylmorphine. For the former, results were not sensitive to differences in assumptions on health utility valuations for individuals reaching a state of abstinence. For the latter, results were presented at short- and longer-time horizons, and extensive sensitivity analyses confirmed the robustness of the results from the baseline model.
Second, the cost of incarceration as a result of crimes committed was not modelled explicitly, because uncertainty on the probability of incarceration and delays in adjudication and sentencing made attribution of these costs to specific health states in the timeframe of the North American Opiate Medication Initiative impossible without strong assumptions. Because rates of crime with and without charges were higher among participants during relapse than during other health states, and because the methadone cohort spent proportionately more time in relapse, omitting these costs favoured methadone maintenance treatment.
Third, because of a high baseline prevalence of hepatitis C virus infection and a paucity of data on which to base time-variant estimates of costs and consequences associated with this condition, we did not model hepatitis C seroconversion explicitly. The costs and QALY losses associated with transmission of HIV and hepatitis C virus from infected individuals to the broader population were also not modelled explicitly. Because the probability of seroconversion and transmission of either disease is higher during periods of relapse, these omissions underestimate the incremental cost savings and QALYs gained with diacetylmorphine.
Finally, gains in productivity were not incorporated into our study, because employment outcomes in the North American Opiate Medication Initiative did not show any significant changes in either treatment arm (unemployment rate 71.2% at baseline and 71.7% at 12 months).
Using mathematical modelling to extrapolate results from the North American Opiate Medication Initiative, we found that a treatment strategy featuring diacetylmorphine may be more effective and less costly than methadone maintenance treatment among people with chronic opioid dependence refractory to treatment. Our model indicated that diacetylmorphine would decrease societal costs, largely by reducing costs associated with crime, and would increase both the duration and quality of life of treatment recipients.