Medication Adherence in Cystic Fibrosis: Three Methods Tell Three Different Stories

Lieke Roeke, Liesbeth I van de Ven, Steffie E M Vonk, et al.

Summary: This cross-sectional Dutch single-center study assessed medication adherence in 43 people with cystic fibrosis (pwCF) — children and adults — using three complementary methods: pharmacy refill data (medication possession ratio, MPR), self-reported adherence (MARS-5 questionnaire), and structured medication reviews conducted by pharmacists. Adherence to CFTR modulators was consistently high across all three methods (72–92%), while adherence to supportive therapies (vitamins, pancreatic enzymes, inhalers, nebulizers) was substantially lower and more variable (56–78%). Structured medication reviews identified four non-adherent patients missed by the other two methods and uncovered 51 drug-related problems (DRPs) across 41 of 43 participants, all of which led to accepted clinical interventions.

Why it matters: The finding that adherence to CFTR modulators is considerably higher than adherence to supportive therapies is clinically important. Patients appear to prioritize — consciously or not — the therapy most visibly transformative in their disease experience. The practical implication is that supportive therapies, despite being fundamental to nutritional status, pulmonary function, and long-term outcomes, may be quietly underused even in motivated, clinic-engaged populations. The demonstration that structured medication reviews added actionable clinical information beyond what refill data and self-report captured is a meaningful operational finding for CF care teams considering how to deploy pharmacist resources.

Expert perspective: The study is methodologically straightforward and appropriately modest in its claims. The sample size of 43 patients from a single Dutch tertiary center is small — this is a feasibility and hypothesis-generating study — and restricts generalizability considerably. Patients attending a specialized academic CF center are not representative of the broader CF population and almost certainly represent a more adherent, more engaged subset. Adherence estimates from this group will likely overestimate adherence in community or less-resourced settings.

The three-method comparison is the study's most interesting contribution. Each method captures something different: MPR reflects dispensing behavior, MARS-5 reflects self-perception of adherence, and medication reviews reveal clinical complexity — polypharmacy, practical barriers, unintentional non-adherence, or inappropriate prescribing. The notably lower CFTR modulator adherence detected by medication review compared to MPR (72% vs. 92%) confirms that pharmacy refill data, while convenient and scalable, may overestimate true medication-taking behavior. Patients can possess a medication without taking it reliably.

The finding that all 51 proposed DRP interventions were accepted by treating physicians warrants a moment of reflection: this could reflect the genuine quality of pharmacist recommendations, or it could reflect social dynamics within a small team operating within the same institutional culture. Independent validation would strengthen this claim. The cross-sectional design cannot address whether medication reviews actually improve adherence over time or produce measurable clinical benefit — that requires a longitudinal or interventional design with a comparison group.

From a real-world data perspective, this study demonstrates something important for CF registries that rely on administrative pharmacy data: refill-based and patient-reported measures give incomplete and sometimes discordant pictures of adherence. Structured medication reviews are resource-intensive and unlikely to be feasible at registry scale, but their findings here could inform the development of better adherence proxies or trigger criteria for targeted pharmacist review.

Relevance: Cystic Fibrosis

Source: https://pubmed.ncbi.nlm.nih.gov/42667119/

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