No interaction studies have been performed.
Budesonide is primarily metabolized by cytochrome P450 3A4 (CYP3A4). Inhibitors of this enzyme, e.g. ketoconazole, itraconazole, HIV protease inhibitors and grapefruit juice, can therefore increase systemic exposure to budesonide several times (see Precautions). Since there is no data to support a dosage recommendation, the combination should be avoided. If this is not possible, the period between treatments should be as long as possible and a reduction of the budesonide dose could also be considered. Budesonide is unlikely to inhibit other drugs metabolized via CYP3A4, since budesonide has low affinity to the enzyme.
Concomitant treatment with CYP3A4 inducers such as carbamazepine may reduce budesonide exposure, which may require a dose increase.
Corticosteroid interactions that may present a significant hazard to selected patients are those with heart glycosides (increased effect due to reduced potassium levels) and diuretics (increased elimination of potassium).
Increased plasma concentrations of and enhanced effects of corticosteroids have been observed in women also treated with oestrogens and contraceptive steroids, but no such effect has been observed with budesonide and concomitant intake of low-dose combination oral contraceptives.
Although not studied, concomitant administration of cholestyramine or antacids may reduce budesonide uptake, in common with other drugs. Therefore these preparations should not be taken simultaneously, but at least two hours apart.
At recommended doses, omeprazole does not affect the pharmacokinetics of oral budesonide, whereas cimetidine has a slight but clinically insignificant effect.