An Ultrasensitive LC-APPI-MS/MS Method for Simultaneous Determination of Ciclesonide and Active Metabolite Desisobutyryl-Ciclesonide in Human Serum and Its Application to a Clinical Study

Background The development of more efficient drug delivery devices for ciclesonide inhalation products requires an ultrasensitive bioanalytical method to measure systematic exposure of ciclesonide (CIC) and its active metabolite desisobutyryl-ciclesonide (des-CIC) in humans. Method Serum sample was extracted with 1-chlorobutane. A reversed-phase liquid chromatography coupled with atmospheric pressure photoionization–tandem mass spectrometry (LC-APPI-MS/MS) method was used for quantification of 1–500 pg/mL for both analytes in a 0.500-mL serum. The analysis time was 4.7 min/injection. CIC-d11 and des-CIC-d11 were used as the internal standards. Results Calibration curves showed good linearity (r2 > 0.99) for both analytes. This novel method was precise and accurate with interassay precision and accuracy of all within 9.6% CV and ± 4.0% bias for regular QC samples. Extraction recovery was approximately 85% for both analytes. Serum samples are stable for 3 freeze–thaw cycles, 24 h at bench top, and up to 706 days at both −20 °C and −70 °C. This method was successfully used to support a pharmacokinetic (PK) comparison between the inhalation suspensions and an inhalation aerosol of ciclesonide in healthy participants. The method robustness was also supported by the good incurred sample reanalysis reproducibility. Conclusion APPI, a highly selective and sensitive ionization source, made possible for quantifying CIC and des-CIC with a lower limit of quantification (LLOQ) of 1 pg/mL in human serum by LC-MS/MS. A 10-fold sensitivity improvement from the most sensitive reported method (LLOQ, 10 pg/mL) is essential to fully characterize the PK profiles of CIC and des-CIC in support of the clinical development of the ciclesonide-related medications for patients.