Mechanism of Trimethoprim’ action is:

Correct Answer: B

Rationale: Rationale: Trimethoprim inhibits dihydropteroate reductase, an enzyme in the folate synthesis pathway in bacteria, disrupting DNA and protein synthesis. This leads to bacterial cell death. Cyclooxygenase (Choice A) is targeted by NSAIDs, not trimethoprim. Dihydropteroate synthase (Choice C) is targeted by sulfonamides, not trimethoprim. DNA gyrase (Choice D) is targeted by fluoroquinolones, not trimethoprim. Therefore, Choice B is correct for trimethoprim's mechanism of action.

Correct Answer: B

Rationale: Step-by-step rationale: 1. Estrogens are contraindicated in most cancers due to their potential to promote cancer growth. 2. However, in prostate cancer, estrogens can be used as a form of androgen deprivation therapy. 3. Estrogen therapy in prostate cancer helps suppress testosterone production, slowing cancer growth. 4. Hence, the correct indication for estrogens in oncological practice is prostate cancer. Summary: A, C, and D are incorrect because estrogen therapy is not indicated in leukemia, endometrial cancer, or brain tumors due to the risk of promoting cancer growth. Prostate cancer is the exception where estrogens can be beneficial for treatment.

Correct Answer: B

Rationale: The correct answer is B: Atrial fibrillation. Atrial fibrillation is characterized by irregular and rapid heart rhythm originating in the atria. This is the most likely disorder based on the given information, as it matches the symptoms described. Premature ventricular contractions (A) are extra, abnormal heartbeats originating in the ventricles. Second-degree atrioventricular block (C) is a conduction disorder between the atria and ventricles. Polymorphic ventricular tachycardia (D) is a serious arrhythmia characterized by irregular heartbeats. However, based on the patient's symptoms, atrial fibrillation is the most likely diagnosis.

Correct Answer: B

Rationale: The correct answer is B: Atrial fibrillation. Atrial fibrillation can cause dizziness and near-syncope due to irregular and rapid heart rates leading to decreased cardiac output. Premature ventricular contractions, second-degree atrioventricular block, and polymorphic ventricular tachycardia are less likely to cause these symptoms in the absence of additional complications like heart failure or structural heart disease. In this case, atrial fibrillation is the most likely cause based on the patient's symptoms and age.

Correct Answer: D

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.