To compare: (1) rates of adherence to asthma controllers (ACs) between patients with asthma alone (A) and patients with asthma and comorbid depression (A + D); (2) rates of adherence to AC between patients who adhere to antidepressants and patients who do not adhere to antidepressants; and (3) asthma-related healthcare costs between the A and A + D groups.Methods
Texas Medicaid insurance claims from 1 January 2007 to 31 October 2011 were extracted for adults (18–63 years) diagnosed with asthma with at least two fills of the same AC (inhaled corticosteroids, long-acting beta agonists, fixed-dose combinations (FDC) and leukotriene modifiers) in the A group, and at least two antidepressant claims in the A + D group. Proportion of days covered (PDC) was used to assess adherence to antidepressants and AC, while controlling for demographics, chronic disease score (CDS) and AC therapy type (monotherapy, FDC, dual therapy). Asthma-related healthcare costs included asthma-related prescriptions, inpatient and outpatient costs. Descriptive statistics, Wilcoxon test and regression analyses were used.Key findings
The patients (n = 3626) were 40.1 ± 14.0 years, primarily women (75.0%), Caucasians (37.3%), FDC therapy users (56.3%), with CDS = 0 (74.2%). Results showed that compared to the A group (n = 3400), patients in the A + D group (n = 226) were 1.6 times more likely to adhere (PDC ≥50%) to their AC (odds ratio (OR) = 1.596; 95% confidence interval (CI) = 1.198–2.128; P < 0.001). Compared to patients who do not adhere to antidepressants (PDC <80%) (n = 140), patients who adhered to antidepressants (PDC ≥80%) (n = 86) were 2.5 times more likely to adhere (PDC ≥50%) to AC, while controlling for covariates (OR = 2.517; 95% CI = 1.304–4.855; P = 0.006). After controlling for covariates, compared to the A group, the A + D disorder group had significantly lower total asthma-related healthcare costs (P < 0.001).Conclusions
In the A + D group, the higher costs of asthma-related prescriptions was offset by the lower costs of inpatient and outpatient claims. Patients in the A + D group should be encouraged to adhere to both their ACs and antidepressants.