Assessment of Potential Factors Influencing Attention-Deficit/Hyperactivity Disorder Drug Adherence: A Database Study

First-line treatment for Attention-Deficit/Hyperactivity Disorder (ADHD) is pharmacological but is associated with poor success rates in adults. The potential to discontinuously use stimulants may confound adherence assessment. Approximately 30-50% of adults with ADHD will experience depressive episodes, and associated treatment with antidepressants is generally recommended. It can therefore be expected that patients with a formal F90 diagnosis would show higher medication adherence than patients without a diagnosis and that the simultaneous use of antidepressants would increase adherence to ADHD medication. The primary aim was to explore the influence of factors of ADHD diagnosis and comorbid antidepressant use on stimulant adherence. A retrospective, longitudinal pharmacoepidemiological study was conducted on South African community pharmacy dispensing records for 2012-2016 for all patients aged between 18 and 40 years with any record of receiving a drug classified as "Central nervous system other" by the MIMS in 2015. Patients endorsed with an ADHD-linked diagnostic code (F90) were identified and contrasted with those receiving ADHD-indicated medication in the absence of a confirmatory diagnostic code. Two methods were applied to assess adherence to ADHD and/or depression treatment drugs: monthly medicine plotting and Proportion of Days Covered (PDC). Patients were classified as being more or less adherent based on monthly medicine plotting criteria. A study population of 89 patients was identified: 50 had F90 diagnostic codes and 39 were classified as "Non F90". Adherence as measured based on PDC was generally higher for antidepressant use than for methylphenidate for patients classified as being more adherent. A trend towards higher consumption of antidepressants was shown for the treatment-adherent group. Diagnostic code distinction revealed significantly higher adherence rates to methylphenidate for F90 code patients. Adherence rates to antidepressants appeared to be generally higher for non-F90 patients. Many factors may influence adherence to ADHD-indicated drugs; however, the impact of a confirmed diagnosis may be a strong determinant of motivation to be adherent to ADHD pharmacotherapy.