Aims: To determine the basal pharmacokinetics, lung uptake and plasma cortisol suppression for two commonly prescribed inhaled corticosteroids.
Methods: Twenty-one subjects (13 healthy and 8 mild asthmatic patients) received fluticasone propionate via a chlorofluorocarbon-propelled pressurized metered-dose inhaler (pMDI) (healthy subjects only) and Diskus and budesonide via Turbuhaler, 1000 microg twice daily for 7 days. Intravenous doses (200 microg) of both compounds were used as references. Plasma concentrations of fluticasone and budesonide were determined during 48 h by liquid chromatography plus tandem mass spectrometry (LC-MS-MS). Plasma concentrations of cortisol were determined by LC-MS every second hour for 24 h at baseline, and following each treatment.
Results: The volume of distribution was found to be larger and the elimination half-life and mean absorption time longer for fluticasone than for budesonide. The systemic availability of budesonide via Turbuhaler (39%) was significantly higher than that of fluticasone via Diskus (13%) (ratio 3.0 [2.5, 3.6] with 95% confidence interval [CI]), and via pMDI (21%) (ratio 1.8 [1.3, 2.3]). In addition, at steady state the systemic availability of fluticasone via pMDI was significantly higher than via Diskus (ratio 1.6 [1.1, 2.2]). The lung deposition of budesonide via Turbuhaler was 2.2-fold [1.7, 2.9] higher than that of fluticasone pMDI and 3.4-fold [2.8, 4.0] higher than that of fluticasone Diskus. In addition, the lung deposition of fluticasone via pMDI was 1.5-fold [1.1, 2.9] higher than that via the Diskus inhaler. Plasma cortisol (24 h) was significantly reduced vs baseline for all three treatments. The cortisol concentration vs baseline was 12% for fluticasone pMDI, which was significantly lower (ratio 0.32 [0.24, 0.42]) than that for fluticasone Diskus (39%), and for budesonide Turbuhaler (46%) (ratio 0.27 [0.21, 0.37]). The plasma cortisol concentration did not differ significantly between treatments with fluticasone Diskus and budesonide Turbuhaler (ratio 0.87 [0.65; 1.15]).
Conclusions: Budesonide and fluticasone differ in their pharmacokinetic properties in that although clearance is the same, the rate of uptake and elimination is slower for fluticasone. Despite a significantly higher pulmonary availability of budesonide via Turbuhaler, the plasma cortisol suppression is less than that of fluticasone via pMDI and similar to that of fluticasone via Diskus. There is no indication of any difference between healthy subjects and mild asthmatic patients in the pharmacokinetics and plasma cortisol suppression of fluticasone and budesonide.