Correct Answer: A

Rationale: The correct answer is A. The kidneys are crucial in maintaining acid-base balance by removing hydrogen ions to decrease acidity and retaining bicarbonate ions to increase alkalinity. Choice B is incorrect because the conversion of ammonia into urea is related to nitrogen waste excretion, not acid-base balance. Choice C is incorrect as aldosterone regulates sodium levels, not acid-base balance. Choice D is also incorrect as renin is involved in regulating blood pressure, not acid-base balance.

Correct Answer: D

Rationale: The correct answer is D: Use of nitrates. Sildenafil (Viagra) is contraindicated in patients taking nitrates due to the risk of severe hypotension. Nitrates and sildenafil both cause vasodilation, and the combination can lead to a dangerous drop in blood pressure. Choice A, peptic ulcer disease, is not a contraindication for sildenafil use. Choice B, a history of myocardial infarction, is not a contraindication unless the patient is also taking nitrates. Choice C, recent use of antihypertensive medications, is not a contraindication but requires caution as the combination can lead to additive effects lowering blood pressure.

Correct Answer: B

Rationale: The correct answer is B: Increased risk of cardiovascular events. Testosterone therapy can lead to an increased risk of cardiovascular events such as heart attacks and strokes, especially in older patients. Monitoring for signs and symptoms of cardiovascular issues is crucial when administering testosterone therapy. Choices A, C, and D are incorrect because testosterone therapy does not typically lead to an increased risk of breast cancer, liver dysfunction, or prostate cancer.

Correct Answer: C

Rationale: The correct answer is C. Oral contraceptives can be less effective when taken with certain antibiotics due to potential drug interactions. It is crucial for patients to be informed about this to consider additional contraceptive methods during antibiotic therapy. Choice A is incorrect because while oral contraceptives are highly effective, they are not 100% foolproof. Choice B is incorrect as it may give the impression that immediate protection is conferred, which is not the case. Choice D is incorrect as taking oral contraceptives with food does not significantly impact their effectiveness.

Correct Answer: A

Rationale: The correct answer is to take the medication at the same time each day to maintain consistent hormone levels and effectiveness. Consistency in timing helps regulate the hormone levels in the body, ensuring the medication's optimal benefit. Choice B is incorrect as there is no specific need to avoid sun exposure with this medication. Choice C is incorrect because discontinuing the medication without consulting the healthcare provider may not be safe. Choice D is incorrect as medroxyprogesterone acetate is typically taken orally and not applied topically once a week.