While therapeutic drug monitoring should be performed at trough, a drug level ≥4.9 μg/mL obtained during the first 9 days predicts a therapeutic trough drug level with reasonable confidence.

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Background: Accurate definition of the gastroduodenal and ileocaecal junctions (GDJ, ICJ) is essential for the measurement of regional transit times. Aims:To compare the assessment of these landmarks using the novel gas-sensing capsule and validated wireless motility capsule (WMC), and to evaluate intra-subject variance in transit times Methods: Healthy subjects ingested the gas-sensing capsule and WMC tandemly in random order. Inter-observer agreement was evaluated by intra-class correlation coefficient (ICC). Agreement between the paired devices' transit times was assessed using Bland-Altman analysis; coefficient of variation was performed to express intraindividual variance in transit times. Similar analyses were completed with tandemly ingested gas-sensing capsules. Results:The inter-observer agreement for landmarks for both capsules was excellent (mean ICC ≥0.97) in 50 studies. The GDJ was identifiable in 92% of the gas-sensing capsule studies versus 82% of the WMC studies (p = 0.27); the ICJ in 96% versus 84%, respectively (p = 0.11). In the primary cohort (n = 26), median regional transit times differed by less than 6 min between paired capsules. Bland-Altman revealed a bias of −0.12 (95% limits of agreement, −0.94 to 0.70) hours for GDJ and − 0.446 (−2.86 to 2.0) hours for ICJ. Similar results were found in a demographically distinct validation cohort (n = 24). For tandemly ingested gas-sensing capsules, coefficients of variation of transit times were 11%-35%, which were similar to variance between the paired gas-sensing capsule and WMC, as were the biases. The capsules were well tolerated.Conclusions: Key anatomical landmarks are accurately identified with the gas-sensing capsule in healthy individuals. Intra-individual differences in transit times between capsules are probably due to physiological factors. Studies in populations with gastrointestinal diseases are now required.