Dose-proportional pharmacokinetics of budesonide inhaled via Turbuhaler

The present pharmacokinetic study was undertaken to determine the dose proportionality of three different doses of budesonide-400 microg, 800 microg or 1600 microg administered twice daily by a dry-powder inhaler (Turbuhaler ) in adult patients with mild asthma.

A total of 38 patients received budesonide by inhalation, 13 received 400 microg twice daily, 12 received 800 microg twice daily and 13 received 1600 microg twice daily. Mean FEV1 at inclusion was 3.4, 4.0 and 3.9 l min-1 in the three groups, respectively. Blood samples were taken after a single dose, and after 3 weeks of daily treatment, for pharmacokinetic evaluation. Plasma concentrations of budesonide were determined by liquid chromatography plus mass spectrometry.

Eleven evaluable patients remained in each dose group. Mean time to peak budesonide plasma concentration (tmax ) was short (0.28-0.40 h) and did not differ between treatment groups. Budesonide concentrations declined rapidly thereafter, indicating efficient pulmonary absorption and rapid elimination with a half-life of approximately 3 h. Cmax was 1. 4(2.0) nmol l-1 (single (repeated) doses), 2.6(3.6) nmol l-1 and 5. 4(6.4) nmol l-1 after 400, 800 and 1600 microg twice daily, respectively. The corresponding results for the area under the plasma concentration vs time curve (AUC) were 271(325), 490(628) and 915(1096) nmol l-1 min. Ninety percent confidence intervals for pairwise dose-normalized Cmax and AUC comparisons between groups were large but contained unity in all cases, thus indicating dose-proportional pharmacokinetics. Regression on analysis supported these findings. Mean AUC after repeated doses (AUC(0,12 h,RD)) was on average 23% higher than the mean AUC after single doses (AUC(0, infinity,SD)(P=0.04) with no significant differences between doses, indicating slight accumulation following bid dosing.

In this relatively small study, budesonide inhaled via Turbuhaler appeared to have dose-proportional pharmacokinetics, both within and above the clinically recommended dose range for asthmatic patients.