Pharmacokinetic interactions: The metabolism of budesonide is primarily mediated by CYP3A4. Inhibitors of this enzyme, e.g. ketoconazole, itraconazole and ritonavir may therefore increase systemic exposure to budesonide. This is of limited clinical importance for short-term (1-2 weeks) treatment with potent CYP3A4 inhibitors, but should be taken into consideration during long-term treatment with potent CYP3A4 inhibitors.
Pharmacodynamic interactions: Beta-adrenergic blockers (including eye drops) can weaken or inhibit the effect of formoterol.
Budesonide and formoterol have not been observed to interact with any other drug used in the treatment of asthma.