The drug inhibits the ubiquitous enzyme carbonic anhydrase:

Correct Answer: A

Rationale: The correct answer is A: Acetazolamide (Diamox). Acetazolamide is a carbonic anhydrase inhibitor, primarily used to treat glaucoma and altitude sickness. Carbonic anhydrase is an enzyme that catalyzes the reversible hydration of carbon dioxide to bicarbonate and protons. By inhibiting this enzyme, acetazolamide reduces the production of aqueous humor in the eye and increases urinary bicarbonate excretion. Furosemide (B), Hydrochlorothiazide (C), and Spironolactone (D) are not carbonic anhydrase inhibitors and work through different mechanisms to treat conditions like hypertension and edema.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Isoniazid is a first-line drug specifically used to treat mycobacterial infections like tuberculosis. 2. It works by inhibiting cell wall synthesis of mycobacteria. 3. Streptomycin, Rifampin, and Kanamycin are also used for mycobacterial infections, but they are effective against a broader range of bacteria. 4. Streptomycin targets protein synthesis, Rifampin inhibits RNA synthesis, and Kanamycin disrupts protein synthesis. 5. Therefore, choice A, Isoniazid, is the correct answer as it targets mycobacteria specifically.

Correct Answer: B

Rationale: The correct answer is B because piperazine works by blocking acetylcholine transmission at the myoneural junction, leading to paralysis of helminthes. This impairs the ability of the worms to move and causes them to be expelled from the body. The other choices are incorrect because: A: Inhibiting microtubule synthesis and impairing glucose uptake is not the mechanism of action of piperazine. C: Inhibiting oxidative phosphorylation is not how piperazine works. D: Increasing cell membrane permeability for calcium leading to paralysis and death is not the mechanism of action of piperazine.

Correct Answer: B

Rationale: Step-by-step rationale: 1. Vincristine is a vinca alkaloid, not a nitrosourea derivative. 2. Carmustine, Lomustine, and Semustine are all nitrosourea derivatives. 3. Therefore, the correct answer is B (Vincristine). Summary: Vincristine is not a nitrosourea derivative, unlike Carmustine, Lomustine, and Semustine.

Correct Answer: C

Rationale: The correct answer is C: Flecainide. Flecainide is a class I antiarrhythmic drug that can cause proarrhythmia, leading to exacerbation of arrhythmias and increased risk of sudden cardiac death. It is known to cause ventricular tachycardia and ventricular fibrillation, which could manifest as the patient's signs and symptoms. Mexiletine (A) and Lidocaine (D) are also class I antiarrhythmics, but they are less likely to cause the described symptoms compared to Flecainide. Sotalol (B) is a class III antiarrhythmic drug and would not typically present with the same signs and symptoms as Flecainide.