LC-HRMS/MS study of the prodrug ciclesonide and its active metabolite desisobutyryl-ciclesonide in plasma after an inhalative administration to horses for doping control purposes.

Ciclesonide (CIC) is the first inhaled highly potent corticosteroid which does not cause any cortisol suppression. It has been developed for the treatment of asthma in human and more recently in equine. CIC is the active compound of Aservo® EquiHaler® (Boehringer Ingelheim Vetmedica GmbH), the pre-filled inhaler generating a medicated mist based on Soft MistTM technology. This prodrug is rapidly converted to desisobutyryl-ciclesonide (des-CIC), the main pharmacologically active compound. Due to its anti-inflammatory properties CIC is prohibited for use in horse competitions. To set up an appropriate control, the determination of detection times and screening limits are required. Therefore, a highly sensitive analytical method based on Supported Liquid Extraction (SLE) combined with Liquid Chromatography - High Resolution tandem Mass Spectrometry (LC-HRMS/MS) was developed to detect CIC and its active metabolite des-CIC in plasma. The lower limit of detection of CIC and des-CIC was approximately 1 pg/mL in plasma. After a pilot study conducted on a single horse at the recommended dose (8 actuations twice daily corresponding to 5.5 mg/day for the first five days, followed by 12 actuations once daily corresponding to 4.1 mg/day in the last five days), the same protocol was applied in the main study using six-horses. In all horses, CIC and des-CIC levels were less than 5 and 10 pg/mL, respectively, at 36 hours after the end of the administration. The outcome of this risk assessment study should be useful to draw any recommendations for horse competitions.