BOSTON – Nearly one-third of patients on antidepressant pharmacotherapy in a large-scale analysis did not take their original antidepressant dose as prescribed within the 6 months prior to dose escalation, a study has shown.
The findings suggest that the lack of adequate treatment response that drives dosage increases in many patients might be linked to suboptimal medication adherence rather than to dose insufficiency, Dr. David J. Muzina reported at the institute.
To evaluate patient nonadherence to chronic antidepressant therapy and a resulting upward dosage titration of the same medication, Dr. Muzina of Medco Health Solutions Inc. and his colleagues identified 53,530 patients from Medco's administrative patient claims database who were on antidepressant medications at the same dosage level for at least 6 months, followed by a subsequent submission of claims for a higher dose.
Patients with only one claim for antidepressant medication in a 6-month period were excluded from the analysis, as were those taking multiple antidepressants, Dr. Muzina explained.
To measure adherence status – which was determined by the proportion of days the patient possessed a supply of the medication, or the medication possession ratio (MPR) – researchers required a minimum of two claims for the same antidepressant drug. According to the National Committee for Quality Assurance's antidepressant performance measures, adherence was defined as an MPR of at least 80%, Dr. Muzina said.
With respect to patient demographics and prescription characteristics, the study cohort was predominantly female (72%), with a mean age of 51 years. More than two-thirds of the sample (68%) filled their antidepressant prescriptions at retail pharmacies, and 62% received generic medications, Dr. Muzina said. Most of the prescriptions were ordered by nonpsychiatrists, with only 15% ordered by psychiatrists; nearly half of the 49,524 patients for whom Chronic Disease Scores (CDS) were available had scores indicating a high degree of comorbidity, he said. Of the full study cohort, “only 70.3% were adherent to their antidepressant medication in the 6 months prior to their dosage increase. Nearly 30% were nonadherent,” Dr. Muzina reported.
Among the nonadherent patients, “one in four was in possession of their prescribed medication during less than 3 months of the 6-month period,” he said.
An analysis of medication adherence by study subgroup – including age, sex, comorbidity, pharmacy channel (mail vs. retail), formulation (brand vs. generic), and prescriber (psychiatrist vs. nonpsychiatrist) – showed significant differences for all but the type of clinician prescriber, Dr. Muzina said, noting that similarly high rates of nonadherence were observed among the psychiatrist (30.4%) and nonpsychiatrist (29.5%) groups.
Regarding pharmacy channel and formulation, 19.2% of patients who filled their prescriptions by mail were nonadherent, which was significantly lower than the 34.6% of those who used a retail pharmacy.
Those receiving generic-only drugs had a small but significantly higher nonadherence rate (30.2%) than the 28.9% rate that was observed among patients receiving brand-name drugs, according to Dr. Muzina.
Older age, male sex, and a higher CDS – perhaps because of the increased interaction with clinicians required by sicker patients – were also associated with significantly improved adherence relative to their respective corollaries, he said.
Although the study did not investigate the reasons for patient nonadherence, some possibilities include undesired or intolerable side effects, negative stigma, and forgetfulness, Dr. Muzina hypothesized.
The findings are limited by the study's retrospective design and the use of an administrative claims database, which doesn't provide certain relevant clinical information, according to Dr. Muzina. However, he suggested that the results indicate that clinicians should investigate and address adherence issues in all patients on antidepressant medications prior to prescribing a dose increase “to enable patients with depression to fully benefit from their medications.”
Additionally, factors associated with adherence to antidepressant treatment should be investigated in future studies, he said.