Dydrogest Drug Interactions

Data from in vitro studies show that Dydrogesterone and its main metabolite 20α-dihydrodydrogesterone (DHD) may be broken down by the P450 cytochrome isoenzymes 3A4 and 2C19.
The metabolisation of Dydrogesterone may therefore be increased by concomitant use of substances known to induce these isoenzymes, such as anticonvulsants (e.g. Phenobarbital, phenytoin, carbamazepine), anti-infectives (e.g. rifampicin, rifabutin, nevirapine, efavirenz) and herbal preparations containing e.g. St. John's Wort (Hypericum perforatum), valerian root, sage, or Gingko biloba.
Ritonavir and nelfinavir are of course well-known powerful inhibitors of cytochrome enzymes but do in fact have an enzyme-inducing action if they are used concomitantly with steroid hormones.
Clinically an increase in the metabolisation of Dydrogesterone may lead to a reduction in effect and changes in the bleeding pattern. In vitro studies show that Dydrogesterone and DHD enzymes that metabolise CYP substances do not inhibit or induce.