Bosentan is metabolised by the cytochrome P450 isoenzymes CYP2C9 and CYP3A4 and is also an inducer of the same isoenzymes. It may also possibly induce CYP2C19. Interactions may therefore occur with the other drugs that are either metabolised by, or inhibit, these isoenzymes. Use with ciclosporin is contraindicated since plasma concentrations of Bosentan are significantly increased. There is an increased risk of hepatotoxicity if Bosentan is given with glibenclamide and such use should be avoided; the hypoglycemic effect of glibenclamide may also be reduced. Bosentan has reduced the plasma concentrations of some hormonal contraceptives and additional; contraceptive measures are advised.