Pharmacokinetics of Roflumilast. Following oral administration, roflumilast is rapidly absorbed with a tmax of about 1 hour and an 80% bioavailability. Roflumilast shows linear dose-proportional pharmacokinetics over a dose range of 250-1000 ug and plasma disposition half-life is about 10-20 hours making once daily dosing a feasible option. roflumilast is metabolized by CYP3A4 and CYP1A2 enzymes with N-oxide being the principal major metabolite. N-oxide has selectivity for the PDE4 isoenzyme and mainly accounts for roflumilast's in vivo bioactivity. No major interactions have been reported between roflumilast and other COPD medications.