Human plasma quantification of fludrocortisone using liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry after low-dosage administration.

BACKGROUND: Fludrocortisone acetate is given at very low dosage (50 µg) to patients suffering from septic shock with controversial clinical results. However, it is not clear if absorption is effective in these patients. METHODS: An analytical method based upon liquid chromatography coupled to triple quadrupole spectrometry detection with atmospheric pressure chemical ionization interface has been developed for the identification and quantification of fludrocortisone, the active molecule circulating in human plasma. A solid phase extraction of plasma was used after addition of fludrocortisone-D2 as internal standard. Compounds were separated on a C18 column with a gradient of methanol-formate buffer. The ion transitions used to monitor analytes were m/z 381→239 and m/z 381→181 for fludrocortisone and m/z 383→239 and m/z 383→181 for fludrocortisone-D2. RESULTS: Retention times were 4.0 min for both compounds. Calibration curves were linear for fludrocortisone in the 0.1-25 ng/ml range. The limits of detection and quantification were 0.05 ng/ml and 0.1 ng/ml, respectively. The intra- and inter-assay precisions were lower than 10.9% and the recovery was 101.8%. A slight matrix effect by about 10% was observed. Application of the method to a patient in septic shock treated with one 50-µg dose of fludrocortisone acetate has shown a maximal plasma concentration of 0.36 ng/ml obtained after 2h. CONCLUSION: This method allows fludrocortisone pharmacokinetic/pharmacodynamic studies when given at low dosage in an intensive care unit in case of adrenal insufficiency during a septic shock.