Table 1:
Estimates for model parameters in cost-effectiveness analysis of diacetylmorphine versus methadone maintenance treatment for chronic, refractory opioid dependence
| Parameter | Estimate | Distribution | Source |
|---|---|---|---|
| Probability of health state transition | |||
| Methadone state | |||
| Remain in methadone state* | λ = 0.114, γ = 0.643 | Weibull | BC MMTOS |
| Multiplier: Episode 4† | 0.923 (0.033) | Normal | BC MMTOS |
| Multiplier: Episode 5 | 0.965 (0.042) | Normal | |
| Multiplier: Episode 6 | 0.952 (0.041) | Normal | |
| Transition to relapse state | 95.9% | Beta | BC MMTOS |
| Transition to abstinence state | 4.1% | ||
| Diacetylmorphine state | |||
| Remain in diacetylmorphine state* | λ = 0.061, γ = 0.761 | Weibull | NAOMI |
| Multiplier: Episode 4‡ | 0.923 (0.033) | Normal | BC MMTOS |
| Multiplier: Episode 5 | 0.965 (0.042) | Normal | |
| Multiplier: Episode 6 | 0.952 (0.041) | Normal | |
| Transition to relapse state§ | 37.0% | Dirichlet | Rehm et al.44 |
| Transition to abstinence state | 22.4% | ||
| Transition to methadone state | 40.7% | ||
| Relapse state | |||
| Remain in relapse state* | λ = 0.091, γ = 0.672 | Weibull | BC MMTOS |
| Multiplier: Episode 4 | 1.220 (0.048) | Normal | BC MMTOS |
| Multiplier: Episode 5 | 1.350 (0.060) | Normal | |
| Multiplier: Episode 6 | 1.442 (0.056) | Normal | |
| Transition to treatment state | 1 | Fixed | |
| Abstinence state | |||
| Remain in abstinence state* | λ = 0.089, γ = 0.797 | Weibull | Termorshuizen et al.12 |
| Transition to relapse state | 1 | Fixed | |
| Transition to death¶ | |||
| Abstinence state, HIV negative | See Appendix 1, Table A1 | Fixed | Statistics Canada32 |
| Abstinence state, HIV positive, standardized mortality ratio, mean (SD) | 1.47 (1.07, 2.01) | Normal | ATCC45 |
| Relapse state, standardized mortality ratio, mean (SD) | 30.063 (3.169) | Normal | Spittal et al.33 |
| Methadone state, relative risk, mean (SD) | 0.350 (0.087) | Normal | Caplehorn et al.6 |
| Diacetylmorphine state, standardized mortality ratio, mean (SD) | 9.70 (0.17) | Normal | Rehm et al.34 |
| HIV seroconversion** | |||
| Treatment state, mean (SD) | 0.0028 (0.0010) | Beta | Bayoumi et al.38 |
| Relapse state, mean (SD) | 0.0364 (0.0146) | Beta | |
| Abstinence state, mean (SD) | 0.0007 (0.0001) | Beta | |
| QALYs†† | |||
| Methadone or diacetylmorphine state | 0.852 | MVN | NAOMI |
| Relapse state | 0.750 | MVN | NAOMI |
| Abstinence state, HIV negative | See Appendix 1, Table A15 | Beta | Johnson et al.46 |
| Abstinence state, HIV positive, mean (SD) | 0.77 (0.19) | Beta | Anis et al.47 |
| Monthly costs,‡‡Can$ | |||
| Drug treatment | |||
| Methadone, mean (SD) | 329.38 (24.46) | Normal | NAOMI, BC PNET |
| Diacetylmorphine, mean (SD) | 1415.21 (25.68) | Normal | NAOMI |
| HIV infection | 28.30 | Fixed | Wood et al.48 and Krentz et al.49 |
| Hepatitis C virus infection | 673.82 | Fixed | Butt et al.50 and BC PNET |
| Methadone or diacetylmorphine state§§ | |||
| Health resource utilization, HIV positive | 72.10 | MVN | NAOMI |
| Criminal involvement | 950.52 | MVN | NAOMI |
| Criminal charges | 398.82 | MVN | NAOMI |
| Relapse state§§ | |||
| Health resource utilization, HIV positive | 695.98 | MVN | NAOMI |
| Criminal involvement | 8981.28 | MVN | NAOMI |
| Criminal charges | 590.05 | MVN | NAOMI |
Note: ATCC = Antiretroviral Therapy Cohort Collaboration, BC MMTOS = British Columbia Methadone Maintenance Treatment Outcome Study, BC PNET = British Columbia PharmaNet database, MVN = multivariate normal, NAOMI = North American Opiate Medication Initiative, QALY = quality-adjusted life-year, SD = standard deviation. Appendix 1 is available at www.cmaj.ca/lookup/suppl/doi:10.1503/cmaj.110669/-/DC1.
Parameter estimates provided for the time to discontinuation of each health state represent the shape (γ) and scale (λ) parameters of the Weibull distribution. From estimated survival functions, at 12 months, the probability of remaining in methadone treatment was about 47%, 68% in diacetylmorphine treatment, 62% in relapse and 52% in abstinence.
Derived from Cox proportional hazards frailty models on successive episodes of treatment and relapse.36 All multipliers presented are hazard ratios and corresponding standard errors.
Change in duration of successive diacetylmorphine episodes was assumed to be equivalent to change in duration of successive methadone episodes.
Included transition to methadone state (n = 379) and other treatment (n = 28) among all participants alive at the end of follow-up and not lost to follow-up (n = 1001).
Sex-specific estimates used in the model for HIV-negative individuals in the abstinence state are presented in Appendix Table A7. For monthly probabilities of death in the abstinence–HIV positive, diacetylmorphine and relapse states, we multiplied base probabilities by state-specific standardized mortality ratios; for monthly probabilities of death in the methadone state, we multiplied the base probabilities by standardized mortality ratios and relative risks.
Calculations and specific references for state-specific HIV seroconversion are shown in Appendix Table A5.
Calculations are shown in section A2.3 in Appendix Tables A13–A16.
Calculations are shown in section A2.2 in Appendix Tables A8–A14.
For all costs related to health resource use, criminal involvement and criminal charges, trial-based data on utilization/frequency of events was multiplied by unit costs from several sources, detailed in Appendix Table A8. Presented state-specific costs are estimated mean values, given the mean age, HIV status and sex mix of participants in the NAOMI study. Costs were a function of each of these parameters in the cohort simulation model.