Incomplete capture of apremilast in Clinical Practice Research Datalink Aurum: An example of exposure misclassification of specialty treatments in United Kingdom general practice databases.

PURPOSE: Nearly all apremilast users captured in Clinical Practice Research Datalink (CPRD) Aurum have only one prescription, which is inconsistent with its prescribing pattern. The goal of this study was to assess capture of apremilast prescriptions in CPRD Aurum by comparison to CPRD GOLD and general practitioner (GP) questionnaires. METHODS: We compared the number of apremilast prescriptions for patients in Aurum to (1) those in GOLD and (2) those reported by the GPs via questionnaire responses. RESULTS: There were 441 Aurum patients with an apremilast prescription (424 [96%] in England) and 341 GOLD patients (11 [3%]) in England). In Aurum 91% of all patients (and 96% of English patients) had only one apremilast prescription while in GOLD 29% of all patients (and 82% of English patients) had only one prescription. We received questionnaire responses from GPs for 50 of 390 (13%) patients participating in Aurum who had 57 total apremilast exposed months captured in Aurum. GPs reported 8 (16%) patients with only one prescription and a median of 4 (range 1-35) apremilast prescriptions per patient, yielding 463 total months of apremilast exposure. CONCLUSIONS: CPRD Aurum captures only one apremilast prescription for most recorded users, though questionnaire responses indicated most patients received multiple prescriptions. Researchers using any UK GP database should be aware of potential for significant exposure misclassification of apremilast and other treatments classified as specialist or shared care by local Area Prescribing Committees.