This drug may block oxidation of low density lipoproteins (LDL):

Correct Answer: D

Rationale: The correct answer is D: Probucol (Lorelco). Probucol blocks the oxidation of low-density lipoproteins (LDL) by inhibiting the formation of lipid peroxides. This is important in preventing the development of atherosclerosis. Lovastatin (A) works by inhibiting cholesterol synthesis, Nicotinic acid (B) lowers LDL and triglycerides but does not specifically block oxidation, and Gemfibrozil (C) decreases triglyceride levels but does not directly block LDL oxidation.

Correct Answer: A

Rationale: The correct answer is A: Loop diuretics. Loop diuretics are the most potent diuretics because they act on the thick ascending limb of the loop of Henle, where they inhibit sodium and chloride reabsorption, leading to significant diuresis. This mechanism results in a higher diuretic effect compared to other classes of diuretics. Thiazide diuretics (B) act on the distal convoluted tubule and are less potent. Potassium-sparing diuretics (C) work on the collecting duct and have a weaker diuretic effect. Carbonic anhydrase inhibitors (D) work on the proximal tubule and are considered mild diuretics compared to loop diuretics.

Correct Answer: C

Rationale: Cephalosporins are broad-spectrum antibiotics effective against both gram-positive and gram-negative bacteria. They are commonly used when penicillins are ineffective. This makes choice C the correct answer, as it accurately reflects the versatility and effectiveness of cephalosporins. A: Gram-positive microorganisms - Incorrect. Cephalosporins are effective against both gram-positive and gram-negative bacteria. B: Gram-negative microorganisms - Incorrect. Cephalosporins are effective against both gram-positive and gram-negative bacteria. D: Only bacteroide infections - Incorrect. Cephalosporins are effective against a wide range of bacteria, not limited to just bacteroide infections.

Correct Answer: B

Rationale: Step 1: Quinolone derivatives are a class of antibiotics that target bacterial DNA synthesis. Step 2: Nalidixic acid is a first-generation quinolone derivative that inhibits DNA gyrase enzyme. Step 3: Nalidixic acid is effective against gram-negative bacteria, making it an antibacterial drug. Step 4: Nitrofurantoin is a nitrofuran antibiotic, not a quinolone derivative. Step 5: Streptomycin is an aminoglycoside antibiotic that inhibits protein synthesis, not DNA synthesis. Step 6: Metronidazole is an antimicrobial drug used for anaerobic bacteria and protozoa, not a quinolone derivative.

Correct Answer: C

Rationale: Step-by-step rationale: 1. Saquinavir is a protease inhibitor used in the treatment of HIV by blocking viral proteases essential for viral replication. 2. Rimantadine is an antiviral drug used for influenza A virus, not inhibiting viral proteases. 3. Acyclovir is an antiviral drug for herpes simplex virus, working by inhibiting viral DNA synthesis, not proteases. 4. Zalcitabine is a nucleoside analog used for HIV, but it inhibits reverse transcriptase, not viral proteases. Summary: Saquinavir is the correct answer as it specifically inhibits viral proteases crucial for viral replication. The other choices target different viral enzymes or processes, making them incorrect for this question.