Discussion
Our findings show that PwCF have excellent adherence to ETI, but
utilization of other CF medications is lower and declines after
initiation of highly effective modulator therapy. This finding is
consistent with anecdotal experience and a prior small study in
PwCF4.The factors underlying reduced utilization of
many CF medications likely differ from those that historically
influenced medication adherence, since utilization declined even in a
subset of PwCF who had excellent adherence prior to starting ETI.
ETI is not a cure for CF, and current guidelines from the US CF
Foundation do not recommend stopping other CF specific treatments after
starting ETI5. However, findings from the SIMPLIFY
study suggest that individuals with relatively preserved lung function
could discontinue Dorn or HTS without changes in lung
function3, which is consistent with our observations.
However, there are several limitations that could influence our
analysis. We were not able to control for factors such as declining
chest physiotherapy use, which could influence changes in lung function.
Furthermore, we cannot rule out the possibility that evaluation of more
individuals over a longer time frame might reveal relationships that
were not observed in our study. Ongoing decline in
ppFEV1 in PwCF on ETI has not been observed in other
studies6, and we speculate that this is a short term
phenomenon reflecting changes in routines and will stabilize with time.
The discrepancy with prior studies could reflect factors unique to our
center or differences between real world retrospective data and
follow-up data of a clinical trial population.
A decrease in PERT utilization was not expected since the initial
clinical trials have not suggested that ETI improves pancreatic
function. Reduced use of pancreatic enzymes could also reflect ETI
related improvements in other aspects of GI physiology, resulting in
better absorption even with less enzyme replacement.
Another limitation is that this single institution study may not be
representative of the CF population as a whole. Also, MPR may
overestimate actual medication utilization as PwCF continue to fill
medications that they are not actually using. However, MPR has the
advantage that it can be readily assessed in a large population and may
reveal patterns difficult to measure is a more targeted group.