Methods
Dispensing records from the University of North Carolina (UNC) Health
System home delivery pharmacy were used to assess all filled
prescriptions for PwCF prescribed CFTR modulator therapy from Nov 2016
to Aug 2021. To restrict the analysis to those who regularly filled
modulators through our pharmacy, the population was limited to those who
filled ≥3 modulator prescriptions over that time frame. Data was
obtained for medication fills for dornase alpha (Dorn), hypertonic
saline (HTS), and pancreatic enzymes (PERT), and inhaled tobramycin. The
study was approved by the institutional IRB (#21-1137).
Medication utilization was measured as medication possession ratio
(actual months filled/prescribed months, MPR). For each individual, MPR
was calculated over a time interval beginning with the first
prescription of any of these medications and ending with the last
prescription and were calculated separately for the pre- and post-ETI
intervals. For inhaled tobramycin, infrequent pharmacy fills (typically
prescribed every other month) plus intermittent use for acute
exacerbations raised doubts about the accuracy of MPR values, and this
medication was not evaluated further. To exclude individuals who did not
receive medications regularly from our home delivery pharmacy,
individuals with fewer than six total fills for a given medication
within the interval were excluded. For longitudinal evaluation, the
number of pharmacy fills for a given month pre- or post-ETI was
determined for all individuals prescribed the medication. Medications
dispensed for 55-60 days were counted as filled for two months total,
and medications dispensed for 85-90 days counted as three months. MPRs
for the group were calculated as the total number of fills in a given
month for the medication divided by the number of individuals prescribed
the medication in that month.
For associations to lung function, percent predicted
FEV1 (ppFEV1) was extracted from UNC
access to the CF Foundation Patient Registry. To ensure sufficient data
to calculate accurate changes over time, subjects were limited to those
who had at least three ppFEV1 values over at least one
year before and three ppFEV1 values over at least one
year after initiation of ETI. Slope ppFEV1 was
calculated by linear regression separately in both pre- and post-ETI
intervals for each individual. Between group analyses were performed
using Student’s T-test, and correlation analyses by linear regression.