Hormonal contraceptives-progestogen implants

The oral contraceptives are of two main types the combined hormonal contraceptives containing both an oestrogen and a progestogen (monophasic, biphasie, triphasie, or sequential), available as tablets or a patch, and the progestogen-only contraceptives, which are available as tablets (sometimes ealled mini pills), parenteral preparations (implants, depot injections) and intrauterine devices. 

Hormonal contraceptives An interaction of warfarin with hormonal contraceptives has been described in a 33-year-old woman [44 ]. While taking warfarin 38.5 mg/week she switched from a monophasic combined oral contraceptive (ethinylestradiol + nor-ethindrone) to an implantable progestogen-only contraceptive (etonogestrel) 19 days later her INR fell to 1.8 and she required an increase in warfarin dose to 60 mg/week. After 10 months she decided to have the implant removed, and 9 days later her INR rose to 6.5. The warfarin dose was reduced to 55.5 mg/week. She then started to use an oral progestogen-only contraceptive (norethindrone) and the effective warfarin dose was 53.5 mg/ week. The authors hypothesized that the predominant mechanism of this interaction was inhibition of CYP1A2 and CYP2C19 by ethinylestradiol. 

---