Cost-effectiveness of diacetylmorphine versus methadone for chronic opioid dependence refractory to treatment

Abstract

Background: Although diacetylmorphine has been proven to be more effective than methadone maintenance treatment for opioid dependence, its direct costs are higher. We compared the cost-effectiveness of diacetylmorphine and methadone maintenance treatment for chronic opioid dependence refractory to treatment.

Methods: We constructed a semi-Markov cohort model using data from the North American Opiate Medication Initiative trial, supplemented with administrative data for the province of British Columbia and other published data, to capture the chronic, recurrent nature of opioid dependence. We calculated incremental cost-effectiveness ratios to compare diacetylmorphine and methadone over 1-, 5-, 10-year and lifetime horizons.

Results: Diacetylmorphine was found to be a dominant strategy over methadone maintenance treatment in each of the time horizons. Over a lifetime horizon, our model showed that people receiving methadone gained 7.46 discounted quality-adjusted life-years (QALYs) on average (95% credibility interval [CI] 6.91-8.01) and generated a societal cost of $1.14 million (95% CI $736,800-$1.78 million). Those who received diacetylmorphine gained 7.92 discounted QALYs on average (95% CI 7.32-8.53) and generated a societal cost of $1.10 million (95% CI $724,100-$1.71 million). Cost savings in the diacetylmorphine cohort were realized primarily because of reductions in the costs related to criminal activity. Probabilistic sensitivity analysis showed that the probability of diacetylmorphine being cost-effective at a willingness-to-pay threshold of $0 per QALY gained was 76%; the probability was 95% at a threshold of $100,000 per QALY gained. Results were confirmed over a range of sensitivity analyses.

Interpretation: 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 among people with chronic opioid dependence refractory to treatment.

Figure 1:

Dynamics of the cohort model. All patients entered the model in a treatment state (diacetylmorphine or methadone maintenance treatment), which was assumed to be their third attempt at treatment of opioid dependence. Patients assigned to the diacetylmorphine cohort could transition to abstinence, relapse, death or methadone treatment (denoted as “post-diacetylmorphine methadone”). From the methadone or the post-diacetylmorphine methadone state, patients could transition to abstinence, relapse or death. From the abstinence state, patients could transition to relapse or death. From the relapse state, patients could transition to death or to a new treatment episode and a new cycle of health states. The probabilities of transitioning from the treatment and relapse health states differed according to the cycle number.

Figure 2:

Cost-effectiveness acceptability curve for the lifetime horizon, plotting the probability that either treatment strategy (diacetylmorphine or methadone) would be cost-effective for a range of threshold values of societal willingness to pay to gain one quality-adjusted life-year (QALY). The probability of diacetylmorphine being cost-effective at a threshold of $0 per QALY gained (cost-saving) is 76%. At a societal willingness to pay of $100 000 per QALY gained, diacetylmorphine is the cost-effective treatment option with 95% certainty, whereas methadone is the cost-effective treatment option with 5% certainty.

Figure 3:

One-way sensitivity analysis of the effect of changes in the monthly costs related to criminal activity during relapse from values used in the baseline model on the incremental cost-effectiveness ratio of diacetylmorphine versus methadone maintenance treatment. A decrease in monthly costs of about 20%, applied to both treatment strategies, would result in an incremental cost-effectiveness ratio greater than zero (higher costs and higher quality-adjusted life-years) for diacetylmorphine v. methadone.

Figure 4:

One-way sensitivity analyses of the effect of changes in the duration of diacetylmorphine treatment episodes from values used in the baseline model (deterministic analysis) on (A) costs of diacetylmorphine (v. methadone) treatment and (B) quality-adjusted life-years (QALYs). Use of the average duration of a diacetylmorphine treatment episode in the baseline model resulted in an incremental cost of about −$32 000 and 0.47 incremental QALYs. Decreasing the average duration of treatment by 30% would result in diminished incremental costs (from −$32 000 to −$20 000) and diminished incremental QALYs (from 0.47 to 0.28).