Ketoconazole 100 mg twice daily increased the plasma concentrations of oral budesonide (3 mg in single dose) six times as a mean on concomitant administration. When ketoconazole was administered 12 hours after budesonide the concentrations increased three times as a mean. As there are no data for dosage recommendations, the combination should be avoided. If this is not possible, the time interval between ketoconazole and budesonide administrations should be as long as possible. A reduction of the budesonide dose should also be considered. It is likely that also other potent inhibitors of CYP3A4 give a markedly increase of the plasma levels of budesonide. Moreover, concomitant intake of grapefruit juice should be avoided.
Concomitant treatment with drugs inducing CYP3A4 such as carbamazepine probably gives lowered exposure to budesonide. Adjustment of the dose may be necessary.
Elevated plasma levels and enhanced effects of corticosteroids have been observed in women also receiving oestrogens and oral contraceptives, but no effects on the plasma concentrations of budesonide have been observed in cases of concomitant intake of contraceptive pills in low-dose combination.
At recommended doses, cimetidine has a slight but clinically insignificant effect, and omeprazole is without effect on the pharmacokinetics of oral budesonide.
Interaction with cholestyramine or antacids cannot be excluded. A time interval of about 2 hours is recommended between administration of these drugs and budesonide.