Concurrent use of the following drug is likely to cause failure of oral contraception:

Correct Answer: B

Rationale: The correct answer is B: Rifampicin. Rifampicin is an enzyme inducer that can accelerate the metabolism of oral contraceptives, leading to decreased effectiveness and potential contraceptive failure. It induces hepatic enzymes, increasing the metabolism of estrogen and progestin in oral contraceptives, reducing their efficacy. Isoniazid (A), Cimetidine (C), and Propranolol (D) do not have significant interactions with oral contraceptives.

Correct Answer: D

Rationale: The correct answer is D because the progestin component of the combined pill serves multiple purposes. Firstly, it suppresses ovulation by inhibiting the release of an egg from the ovary, preventing pregnancy. Secondly, it helps induce prompt bleeding at the end of the pill course, mimicking a natural menstrual cycle. Lastly, progestin also blocks the increased risk of endometrial carcinoma associated with unopposed estrogen use. Therefore, all of the choices A, B, and C are correct in relation to the purposes served by the progestin component.

Correct Answer: A

Rationale: Step 1: Mifepristone is a progesterone receptor antagonist. Step 2: In the late luteal phase, progesterone levels drop, leading to menstruation. Step 3: By inhibiting progesterone action, mifepristone induces menstruation. Step 4: Therefore, the correct answer is A - induces menstruation. Summary: B is incorrect as mifepristone does not postpone menstruation. C is incorrect as it does not prevent luteolysis but rather triggers it. D is incorrect as mifepristone does not cause decidualization of endometrium.

Correct Answer: D

Rationale: The correct answer is D, "All of the above." Norethindrone, Nafarelin, and Danazol are all beneficial in managing endometriosis. Norethindrone is a progestin that helps regulate menstrual cycles and reduce pain. Nafarelin is a gonadotropin-releasing hormone agonist that suppresses ovarian function, reducing estrogen levels. Danazol is a synthetic androgen that suppresses estrogen production and inhibits the growth of endometrial tissue. Therefore, all three medications address different aspects of endometriosis, making them effective treatment options.

Correct Answer: A

Rationale: Progesterone administration suppresses menstruation by maintaining the endometrial lining. It inhibits the shedding of the endometrium, postponing the onset of menstruation. Choice B and D are incorrect as progesterone thickens cervical mucus and promotes glandular activity, not watery secretions. Progesterone does not sensitize the uterus to oxytocin (Choice C).