To our knowledge, this is the first study that investigated whether LCPPs decrease data availability of low-cost medication dispensing events. We did not find any evidence to support the concern voiced by some researchers that pharmacies may not be sending claims for low-cost generic medications to PBMs. The estimated proportion of patients receiving each anti-diabetic medication was comparable not only across chains, regardless of whether they offered an LCPP, but also before and after the time frame in which chains implemented LCPPs. In addition, from the longitudinal data, we further observed no significant difference in changes in the level and slope of the proportion of low-cost medication use after LCPP implementation between chains with and without LCPP.
In the longitudinal data set, low-cost OHA use has been rapidly increasing from 2002 to 2006. A slower growing of the proportion of low-cost medication use has been observed in chains with and without LCPP in the beginning of 2007. Possible explanation could be an amount of patients dispensed preferred branded antidiabetic medications even the insurance program has encouraged using generic OHAs. In addition, some patients in this population might be eligible for Medicare Part D program when it was implemented in 2006, which we might not capture complete medication dispensing information for these patients.
The proportions for anti-diabetic drugs which are not included in the LCPPs were similar between chains offering LCPPs and those that do not, which increases our confidence in our estimation process. In addition, the similarities of the proportion of patients using each OHA between our estimates based on pharmacy claims and estimates from the MEPS data increase support our belief that our claims-based estimates are reasonable.
From these experiences, we did not find evidence to support the concern that the PBMs do not capture dispensing events of low-cost medications in chains with LCPP. We speculate that because of the level of automation of the submission process in most pharmacies and the minimal cost of transmitting these transactions that, unless a patient pays cash and specifically requests that the pharmacy not share the data with the patient’s payor, the pharmacy will send the claim to the patient’s PBM. To not send in the claim, the technician or the pharmacist would have to change the patient’s payer to "cash", which would require more work than submitting a claim to the third-party when the patient has active prescription drug coverage in their profile.
It is possible that the central Indiana population may not be representative of other populations but the demographics are similar to the overall US population. We only studied OHAs in diabetic patients who have active insurance coverage. Findings may not apply to other medications in the LCPP or to patients without active insurance coverage. In addition, we were not able to directly measure the proportion of patients receiving OHAs to compare with the estimate based on claims transactions, but we believe that our approach of comparing the proportions for patients receiving medications from chains with and without LCPPs are a good proxy. Note that provider orders would not provide a good gold standard since so many prescriptions go unfilled. We might not have identified all diabetic patients and may have included some Type 1 diabetics, but this should not introduce any systematic bias. Further, assignment of patients to pharmacy chains was reasonable based on at least 3 OHA dispensing events during the study period, which might exclude information from patients who had less than three OHA dispensing records in the INPC. However, this assignment may provide information for a more stable study population for each chain.