Study tests predictive model for estimating nonadherence to glaucoma meds

The authors developed and validated a detailed predictive model for estimating the probability of nonadherence to once-daily glaucoma medication.

Several studies have identified risk factors for poor adherence with topical glaucoma medications. Poorer adherers were more likely to be 50 years of age and younger or 80 years of age and older and to be African-American. Factors such as disease severity, medication cost, complexity of the dosing regimen, forgetfulness, inconvenience and side effects have also been associated with nonadherence. Although these studies have provided a better understanding of the relevant risk factors involved in nonadherence, clinicians are still faced with the challenge of integrating these factors into a global assessment of the risk for a particular patient. For this reason, the authors sought to develop a model integrating these risk factors to help estimate an individual's probability of being nonadherent and test the model’s performance in an independent population of glaucoma patients.

The predictive model was developed using data from the Travatan Dosing Aid (TDA) study and validated in patients who participated in the Automated Dosing Reminder Study (ADRS). Both study protocols had two phases: Phase 1 was an observational cohort study to assess patients' adherence to once-daily prostaglandin therapy, and phase 2 was a controlled study to improve adherence for those found to have low adherence in phase 1.

In both studies, electronic monitoring of eye drop usage was performed for three months. Adherence was calculated as the percentage of days on which a dose was taken within four hours of the average dosing time for that patient. Nonadherence was defined as taking 75 percent or less of the prescribed doses within a window starting two weeks after the baseline visit until two weeks before the follow-up visit. The predictive model uses demographic data and patient responses to four questions to assign a probability of nonadherence.

The risk scoring system developed from the TDA study had good discrimination when applied to the ADRS population, suggesting good generalizability. In both studies, black race, a lower self-reported adherence rate and shorter duration of glaucoma treatment were significantly associated with an increased risk of being nonadherent.

The authors note that patients who perceived that they were not in excellent health were also less likely to take their eye drops regularly. These patients may have inherent difficulties taking any medications. Sicker patients may also pay more attention to their general health status instead of glaucoma-induced vision loss. Patients who admitted to less than ideal use of medications indeed had lower adherence rates. Many reported that they forgot or that it was inconvenient to take drops. Very few reported nonadherence due to cost, side effects or other medical conditions.