Assessing Refill Data Among Different Classes of Antidepressants

Depression affects about 4.4% of the global population.¹ Major depressive disorder (MDD) is currently the fourth highest cause of disability in the world and by 2030 MDD is expected to be third.² Research has determined that 1 in 3 veterans seen in primary care shows depressive symptoms. Of these, 1 in 5 have symptoms severe enough to warrant further evaluation for MDD, and 1 in 10 require treatment.³ With this high rate of depression, optimized treatment strategies are needed, including antidepressants and psychotherapy. Antidepressants have grown in popularity since market entry in the 1950s; currently 1 in 10 US citizens aged ≥ 12 years are prescribed an antidepressant.⁴

Antidepressant Adherence

Antidepressant adherence is crucial for response and remission. Sansone and Sansone reported that, on average, < 50% of patients are adherent to their antidepressant treatment regimen 6 months after initiation (range, 5.4% - 87.6%).⁵ Fortney and colleagues found that, based on patient report, < 20% of veterans maintained at least 80% adherence at 6 months.⁶ Patients who are nonadherent are at an increased risk for relapse and recurrence and are more likely to seek care at an emergency department or to become hospitalized.² In addition to the negative impact on patient outcomes, antidepressant nonadherence may also result in increased economic burden. In the US alone, the annual cost of treating MDD exceeds $210 billion, which will continue to increase if nonadherence is not mitigated.¹

Patient-specific characteristics such as lack of knowledge about proper administration techniques, misguided beliefs, and negative attitudes towards treatment may affect adherence.⁵ In the veteran population, reasons for discontinuation also include lack of perceived benefit and adverse effects, specifically sexual difficulties.⁶ Sociodemographic and other patient characteristics also may be risk factors for nonadherence, including multiple medical comorbidities; substance use disorder (SUD) diagnosis; male gender; younger age; lack of health insurance or a higher medical cost burden; lack of or low involvement in psychotherapy; infrequent follow up visits; and high illness severity.^1,7,8

Appreciating the adherence rates among the different antidepressant classes may help in antidepressant selection. To our knowledge, there have been no prior studies conducted in the veteran population that compared adherence rates among antidepressant classes. Studies in the nonveteran population report differing adherence rates among the antidepressant classes with generally higher adherence in patients prescribed serotonin norepinephrine reuptake inhibitors (SNRIs) and selective serotonin reuptake inhibitors (SSRIs). A retrospective review of commercial, Medicare, and Medicaid claims in > 5000 patients found that SNRIs had a significantly higher 3-month adherence rate based on the portion of days covered model (47%; P < .001) than other antidepressant classes (SSRIs, 42%; other antidepressants, 37%; tricyclic antidepressants [TCAs], 24%).⁷ Monoamine oxidase inhibitors (MAOIs) prescribed to 1% of the study population had the highest adherence rate at 48%.⁷ A study reviewing > 25 000 patient claims sourced from the IBM MarketScan research database (Armonk, NY) found that SSRIs (Odds ratio [OR], 1.26; P < .001) and norepinephrine dopamine reuptake inhibitors (NDRIs) (OR, 1.23; P = .007) had the highest ORs for adherence according to the portion of days covered model, while other serotonin modulators (OR, 0.65; P = .001) and tri/tetracyclic antidepressants (OR, 0.49; P < . 001) had the lowest ORs and were associated with lower adherence.¹