Interaction studies have only been performed in adults.
A major step in roflumilast metabolism is the N-oxidation of roflumilast to roflumilast N-oxide by CYP3A4 and CYP1A2. Both roflumilast and roflumilast N-oxide have intrinsic phosphodiesterase-4 (PDE4) inhibitory activity. Therefore, following administration of roflumilast, the total PDE4 inhibition is considered to be the combined effect of both roflumilast and roflumilast N-oxide. Interaction studies with CYP1A2/3A4 inhibitor enoxacin and the CYP1A2/2C19/3A4 inhibitors cimetidine and fluvoxamine, resulted in increases of the total PDE4 inhibitory activity of 25%, 47% and 59%, respectively. The tested dose of fluvoxamine was 50 mg. A combination of roflumilast with these active substances might lead to an increase of exposure and persistent intolerability. In this case, roflumilast treatment should be reassessed (see Precautions).
Administration of the cytochrome P450 enzyme inducer rifampicin resulted in a reduction in total PDE4 inhibitory activity by about 60%. Therefore, the use of strong cytochrome P450 enzyme inducers (e.g. phenobarbital, carbamazepine, phenytoin) may reduce the therapeutic efficacy of roflumilast. Thus, roflumilast treatment is not recommended in patients receiving strong cytochrome P450 enzyme inducers.
Clinical interaction studies with CYP3A4 inhibitors erythromycin and ketoconazole showed increases of 9% of the total PDE4 inhibitory activity. Co-administration with theophylline resulted in an increase of 8% of the total PDE4 inhibitory activity (see Precautions). In an interaction study with an oral contraceptive containing gestodene and ethinyl oestradiol, the total PDE4 inhibitory activity was increased by 17%. No dose adjustment is necessary in patients receiving these active substances.
No interactions were observed with inhaled salbutamol, formoterol, budesonide and oral montelukast, digoxin, warfarin, sildenafil and midazolam.
Co-administration with an antacid (combination of aluminium hydroxide and magnesium hydroxide) did not alter the absorption or pharmacokinetics of roflumilast or its N-oxide.