Study objective: To assess the effect of health literacy on drug adherence in the context of a pharmacist-based intervention for patients with heart failure.
Design: Post hoc analysis of a randomized controlled trial.
Setting: Inner-city ambulatory care practice affiliated with an academic medical center.
Patients: The original trial enrolled 314 patients with heart failure who were aged 50 years or older and were taking at least one cardiovascular drug for heart failure; 122 patients received the pharmacist intervention (patient education, therapeutic monitoring, and communication with primary care providers), and 192 patients received usual care (regular follow-up with primary care providers). We analyzed the results of 281 patients who had available health literacy and adherence data.
Measurements and main results: Drug adherence was assessed over 9 months using electronic prescription container monitors on cardiovascular drugs. Health literacy was assessed using the Short Test of Functional Health Literacy in Adults (scores range from 0-36, with an adequate literacy score defined as ≥ 23). Taking adherence, defined as the percentage of prescribed drug doses taken by the patient compared with the number of doses prescribed by the physician, was assessed for each group. Patients were a mean ± SD of 63 ± 9 years old, 51% had less than 12 years of education, 29% had inadequate health literacy, and they received a mean ± SD of 11 ± 4 drugs. In the usual care group, taking adherence was greater among patients with adequate (69.4%) than those with inadequate (54.2%) health literacy (p=0.001). In the intervention group, the difference in taking adherence among patients with adequate (77.3%) and inadequate (65.3%) health literacy was not statistically significant (p=0.06). Among patients with inadequate health literacy, the intervention increased adherence (65%, 95% confidence interval [CI] 54-77%) by an order of magnitude similar to that of the baseline adherence of patients with adequate health literacy (69%, 95% CI 65-74%). Multivariable analysis supported the association between health literacy and adherence.
Conclusion: In patients with heart failure, those with adequate health literacy have better adherence to cardiovascular drugs than those with inadequate health literacy. The pharmacist intervention improved adherence in patients with adequate and inadequate health literacy. Health literacy may be an important consideration in drug adherence interventions.
Trial registration: ClinicalTrials.gov NCT00388622.
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