Correct Answer: B

Rationale: The correct answer is B. Metronidazole (Flagyl) is the drug of choice for treating giardiasis, which is a common cause of diarrhea and abdominal distention. Sulfasalazine (Choice A) is used to treat inflammatory bowel disease. Trimethoprim-sulfamethoxazole (Choice C) is commonly used for urinary tract infections and Pneumocystis jirovecii pneumonia. Doxycycline (Choice D) is commonly used to treat various bacterial infections but is not the first-line treatment for giardiasis.

Correct Answer: D

Rationale: The direct effects of antibodies include neutralization, agglutination, and precipitation. Antibodies neutralize pathogens by binding to them and preventing their harmful effects. Agglutination involves the clumping together of pathogens, making it easier for phagocytes to engulf them. Precipitation refers to the process where antibodies bind to soluble antigens, forming large complexes that are easily removed from the body. Phagocytosis, on the other hand, is an indirect effect of antibodies where phagocytes engulf and destroy pathogens opsonized by antibodies, not a direct effect.

Correct Answer: B

Rationale: The correct answer is B: 'Use of nitrates.' Tadalafil (Cialis) is contraindicated in patients using nitrates due to the risk of severe hypotension. Nitrates and tadalafil both cause vasodilation, leading to a synergistic effect that can result in a dangerous drop in blood pressure. Choices A, C, and D are incorrect because a history of hypertension, the use of antihypertensive medications, and a history of peptic ulcer disease are not direct contraindications for tadalafil use.

Correct Answer: B

Rationale: The correct answer is B. Medroxyprogesterone should be taken at the same time each day to maintain consistent hormone levels and effectiveness. Choice A is incorrect because medroxyprogesterone does not necessarily need to be taken with food. Choice C is incorrect as it is typically prescribed continuously rather than intermittently. Choice D is incorrect because patients should not stop the medication if side effects occur without consulting their healthcare provider.

Correct Answer: A

Rationale: The correct answer is A: Levonorgestrel (Plan B). Levonorgestrel is the most commonly prescribed medication for emergency contraception within 72 hours of unprotected intercourse. It is effective when taken within 72 hours after intercourse, with better efficacy the sooner it is taken. Choice B, Mifepristone (RU-486), is not indicated for emergency contraception but is used for medical abortion. Choice C, Ulipristal acetate (ella), is another option for emergency contraception that is effective up to 120 hours after unprotected intercourse. Choice D, Estradiol (Estrace), is not used for emergency contraception.