Is methadone treatment more effective for lower socio-economic status opiate users? Results from a case crossover study in Lazio

Background: Opioid dependence, characterised by socio economic disadvantage and significant morbidity and mortality, remains a serious public health problem in Italy. Mortality is considered a valid indicator for measuring the health impact of the drug use and is associated, on an individual level, with the severity of addiction and the effectiveness of the available option of treatment. In terms of pharmacological options to treat opiate dependence, substitution treatment using methadone is most common in Italy and the protective effect of methadone treatment is widely recognized. Socioeconomic status (SES) is often inversely related to health outcomes and is likely to play a role in the use of psychoactive substances among young individuals, although little consensus exists on the association between SES and substance use or how the two are related.

Aim: To evaluate the effectiveness of the treatment performed by Public Drug Treatment Centres (SerD) in subjects with different socio-economic status (SES).

Methods: A case crossover study was conducted to evaluate the association between treatment and mortality. The OR estimation was performed using a conditional logistic regression model considering the SES as an effect modifier. In the Lazio region, since 1991 the Regional Surveillance System on Drug Addiction has been established. From 2015, this system changed in System on Drug Addiction (SIRD), that collects socio-demographic information as well as treatments provided to drug users by SerD and by therapeutic community operating in Lazio region. Drug users with opioid dependence were enrolled through SIRD, using as inclusion criterion those who received at least one delivery of a substitutive agonist treatment (methadone) between 01/01/2015 and 06/30/2017. Through record linkage with the Hospital Information System and the Tax Registry we reconstructed the information on admissions and mortality of the subjects enrolled in the study. The SES was assigned according to the census of residence section, using a regional ecological indicator built on data from the 2011 Census. Exposure, defined as a pharmacological treatment received by a SerD, was measured at the time of death and at 30 and 60 days prior.

Results: Of the 8531 users with at least one methadone delivery between 2015 and the first semester of 2017, 117 were deceased and therefore eligible. 45.3% of the cases were treated at the time of death, while the same proportion measured at 30 and 60 days before was equal to about 54%. Subjects undergoing treatment were less likely to die than untreated (OR = 0.30 p = 0.010). Considering the interaction with SES, we observed that the protective effect of treatment is more evident in subjects with low / medium-low SES (N = 153, OR = 0.14 p = 0.077), compared to subjects with high / high -medium SES (N = 99, OR = 0.55 p = 0.376).

Conclusion: The regional surveillance system on Drug Addiction is a useful tool for monitoring the health consequences of drug use. We found that substitution treatment was more effective in the more disadvantaged segment of the population of drug addicts, as compared to the group belonging to the higher socio economic level. The study confirms the relevant role of substitution treatment offered by a public system to increase equity of care.