The emergency contraceptive drugs (EC), levonorgestrel (LNG) and ulipristal acetate (UPA), are sensitive substrates of cytochrome P450 3A4 (CYP3A4). In 2016, the label of LNG was updated based on a drug–drug interaction (DDI) study showing a significant decrease in LNG exposure when co‐administered with efavirenz, a known CYP3A4 inducer. DDI between UPA and CYP3A4 inducers are poorly characterized. The aims of this study were to review quantitative data from the literature on DDI with EC, to provide quantitative predictions of DDI between UPA and CYP3A4 inducers, and to identify moderate and severe DDI that may require a dose adjustment. A literature search was performed on pharmacokinetic DDI of LNG and UPA. Quantitative prediction of DDI with UPA was carried out by using the in vivo mechanistic static model (IMSM). Limited information was available on DDI with emergency contraception drugs. For LNG, data from eleven studies were retrieved, including five known CYP3A4 inducers that confirmed a risk of underexposure to LNG when co‐administered with inducers. For UPA, only three studies were identified, including only one CYP3A4 inducer. The IMSM approach indicated that UPA is a sensitive substrate of CYP3A4, with an estimated contribution of 86% of CYP3A4 to oral clearance. Moderate to severe DDI were predicted in 17 cases with CYP3A4 inducers, and dosage adjustments were suggested. This study illustrates the ability of the IMSM approach to inform about the DDI profile of old and new drugs.

ObjectiveTo review the survival modelling used in cost-effectiveness studies evaluating an interventional procedure and to discuss implications for decision-makers.DesignA case study of three economic evaluations that each used immature data from the EVEREST II High Surgical Risk (HSR) Study of transcatheter edge-to-edge repair (TEER) for patients with severe mitral regurgitation (MR) who were at high risk of surgery.SettingEstimation of patient survival in cost-effectiveness studies.ParticipantsThe EVEREST II HSR Study included 78 patients who had TEER of the mitral valve using the MitraClip device and a retrospectively identified control group of 36 patients who received medical management and were followed up for 12 months. Observed survival (TEER arm only) was updated at 5 years.ResultsTwo studies used 12-month observed mortality from EVEREST II HSR to model survival over lifetime horizons. Observed and modelled survival were associated with considerable uncertainty due to short follow-up and small numbers of participants. Modelling control patients’ survival required an approximate 10-fold extrapolation based on 12-month observation of only 38 patients. Observed 5-year survival in the TEER group differed from that less mature follow-up suggesting that survival modelling based on shorter follow-up was unsatisfactory. No public domain data for the control group are available beyond 12-month follow-up so meaningful estimates using mature data for both arms are currently not possible. A third study developed survival models using incompletely reported transitions between MR grades in EVEREST II HSR and mortality rates observed for different MR grades derived from a study in an unrelated population.ConclusionsModelling survival in such small samples followed up for only 12 months is associated with great uncertainty, and cost-effectiveness results based on these analyses should be viewed as premature and used cautiously in reimbursement decisions.

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