Budesonide has not been observed to interact with any drug used for the treatment of asthma.
The metabolism of budesonide is primarily mediated by CYP3A4, a subfamily of cytochrome P450. Inhibitors of this enzyme e.g. ketoconazole and itraconazole, can therefore increase systemic exposure to budesonide. See Precautions.
This is of limited clinical importance for short-term (1-2 weeks) treatment with CYP3A inhibitors, but should be taken into consideration during long-term treatment.
At recommended doses, cimetidine has slight but clinically insignificant effect on the pharmacokinetics of oral budesonide.