Fig. 1: Overview of the study pipeline.

a The procedure begun with a patient performing five-to-six simple exhalations into a SESI–HRMS analytical platform located in the hospital premises. The breath metabolomics fingerprint was acquired in positive and negative-ion mode (5, 6 exhalations per mode). Shortly before the breath test, blood was drawn to evaluate blood/serum concentrations of ASMs. b SESI–HRMS is a real-time, noninvasive, and fast breath-metabolome analysis method. The whole breath test (i.e., positive- and negative-ion mode), lasts typically 10–15 min per patient. Positive-mode TIC from two patients, one receiving VPA and another one receiving LEV, is shown as an example (TIC of patient 29 is inverted to ease visual inspection). c Comparison of the average mass spectra between the two subjects taking VPA and LEV. The inset shows an example of time-trace at m/z 143.1066 (mass spectrum and time-trace of patient 29 inverted to ease visual inspection). For each ion, area under the curve during each exhalation was computed (shaded regions) and normalised by the exhalation time (nAUC). Then, the nAUCs of 5, 6 exhalations were finally averaged to represent mean nAUC of the ion. d This resulted in a 75 × 3252 (measurements × mass spectral features present in at least 10% of total measurements and correlated with exhalations) data matrix (z-score is only used here to ease visual representation; actual downstream analysis was done on raw numbers). e Analysis workflow used to predict VPA serum concentration based on drug-related metabolites. f The workflow used to predict side effects and drug-response scores based on drug-regulated metabolites. See Methods for more detail about panels e and f. Colour key for heatmaps is shown in-between panels e and f.