Methotrexate is:

Correct Answer: B

Rationale: Methotrexate is a folic acid antagonist used in the treatment of various conditions such as cancer, rheumatoid arthritis, and psoriasis. The correct answer is B because methotrexate exerts its pharmacological effects by inhibiting dihydrofolate reductase, an enzyme involved in the synthesis of folic acid. By inhibiting this enzyme, methotrexate disrupts the production of DNA and RNA, leading to the suppression of cell proliferation. Option A, purine antagonist, is incorrect because methotrexate does not directly target purines. Option C, an antibiotic, is incorrect as methotrexate is not used to treat bacterial infections. Option D, an alkylating agent, is incorrect because methotrexate does not work by alkylating DNA. Educationally, understanding the mechanism of action of methotrexate is crucial for healthcare professionals to appropriately prescribe and monitor its use in patients. This knowledge helps in identifying potential drug interactions, side effects, and monitoring parameters to ensure safe and effective treatment outcomes. It also highlights the importance of pharmacological knowledge in tailoring treatment plans to individual patients based on their specific needs and conditions.

Correct Answer: C

Rationale: Chronic fever and posterior cervical lymphadenopathy (Winterbottom’s sign) over two years suggest African trypanosomiasis (sleeping sickness), caused by Trypanosoma brucei gambiense (C), which is chronic in West Africa. T. cruzi (A) causes Chagas disease (cardiac/gastrointestinal), T. b. rhodesiense (B) is acute, Leishmania donovani (D) causes visceral leishmaniasis (splenomegaly), and Onchocerca volvulus (E) causes river blindness—none match the chronic lymphadenopathy pattern.

Correct Answer: B

Rationale: A strict vegetarian avoiding meat, fish, and milk products lacks dietary vitamin B12 (found in animal products), leading to B12 deficiency anemia (B). Iron deficiency (A) is possible but less likely with plant-based iron sources, erythropoietin defects (C) are renal-related, calcium deficiency (D) doesn’t cause anemia, and transferrin production defects (E) are rare—B12 deficiency fits the history.

Correct Answer: C

Rationale: Increased neutrophils, band cells, basophils, eosinophils, and platelets suggest chronic myelocytic leukemia (CML, C), a myeloproliferative disorder with Philadelphia chromosome. AML (A) has blasts, ALL (B) lymphocytosis, high LAP score (D) rules out CML (low LAP), and myeloid:erythroid ratio (E) is nonspecific—CML matches.

Correct Answer: C

Rationale: The testicle is a mixed gland because it has both endocrine functions (secreting testosterone into the bloodstream) and exocrine functions (producing sperm, which is released via ducts). Option A is incorrect as gametes are exocrine products, not endocrine. Option B reverses the definitions, and D is too narrow, as it omits the exocrine role.