Among the subcohort of individuals who received buprenorphine or naltrexone and had at least 1 drug-related poisoning, we conducted within-person longitudinal analyses to evaluate whether buprenorphine or naltrexone use was associated with decreased risk of such events, both among individuals with and without cooccurring SUDs. This analysis used a repeatable-event, case-crossover design previously described in detail.16 In brief, the case-crossover method characterizes each person who experiences the outcome event over time by the presence or absence of treatment with medications. Case periods included days when acute events occurred; control periods encompassed days when such events did not occur, with each individual used as their own control by comparing buprenorphine or naltrexone prescriptions (exposure variable) at the time of event with exposure during control periods (no event). As a within-person analysis, the case-crossover design implicitly controls time-invariant confounding, although time-varying confounding is still an issue. The repeatable-event approach partially mitigates this because time can be included as a covariate.17 The association between drug-related poisoning and medication (buprenorphine or naltrexone) treatment days was estimated using conditional logistic regression.
