Tetracyclines are used to treat:

Correct Answer: B

Rationale: Tetracyclines are used to treat Lyme disease (B), caused by Borrelia burgdorferi, with doxycycline as a first-line oral therapy due to its efficacy against spirochetes and good tissue penetration. They're ineffective against Clostridium difficile (A), where metronidazole or vancomycin is preferred, and may exacerbate colitis. They treat acne vulgaris (C) by reducing Propionibacterium acnes and inflammation, often with topical or systemic forms. They're not used for systemic lupus erythematosus (D), an autoimmune condition managed with immunosuppressants. Non-specific urethritis (original E) responds to tetracyclines like doxycycline for Chlamydia. Their bacteriostatic action on protein synthesis and broad-spectrum coverage make tetracyclines versatile, though photosensitivity and tooth discoloration limit use in certain populations.

Correct Answer: A

Rationale: Foscarnet is indicated in CMV retinitis in AIDS patients (A), a key treatment for this vision-threatening infection, directly inhibiting viral DNA polymerase without needing activation, unlike aciclovir. It treats aciclovir-resistant HSV (B), particularly in immunocompromised patients. It's nephrotoxic (C), requiring hydration and monitoring due to renal tubular damage. It causes fits (D), linked to electrolyte imbalances like hypocalcemia. It's not usually oral/topical (original E is incorrect), given IV. Foscarnet's broad antiviral activity, including against ganciclovir-resistant CMV, makes it vital in advanced HIV, though its toxicity profile demands careful management.

Correct Answer: B

Rationale: Intravenous co-trimoxazole (B) is a first-line treatment for Pneumocystis jirovecii pneumonia (PCP) in HIV patients, combining trimethoprim and sulfamethoxazole to inhibit folate synthesis, highly effective against this opportunistic pathogen. Aztreonam (A) targets Gram-negative bacteria, not PCP. Rifabutin (C) treats mycobacterial infections, not PCP. Pentamidine (D) is an alternative for PCP, used IV or inhaled when co-trimoxazole is contraindicated. Glucocorticoids (original E) are adjunctive if PaO2 <60 mmHg. Co-trimoxazole's synergy, prophylaxis role, and IV option for severe cases make it standard, though rash and hyperkalemia are common, manageable side effects.

Correct Answer: B

Rationale: Cyclophosphamide is an alkylating agent (B), cross-linking DNA to halt cancer cell division, widely used in lymphomas, leukemias, and solid tumors. It's typically combined with other agents (A) in regimens like CHOP for synergy. It causes granulocytopenia (C), a dose-limiting toxicity increasing infection risk. It causes nausea and vomiting (D), moderately to highly emetogenic. Alopecia (original E) is common. Its activation by CYP450 to active metabolites like phosphoramide mustard enhances efficacy, but hemorrhagic cystitis (prevented by mesna) and cardiotoxicity at high doses require careful monitoring.

Correct Answer: A

Rationale: Lopinavir is associated with lipodystrophy syndrome (A), a metabolic complication of protease inhibitors, causing fat redistribution (truncal gain, peripheral loss), linked to mitochondrial toxicity and insulin resistance, often boosted by ritonavir. Hyperglycemia (B) occurs, reflecting metabolic dysregulation. Peripheral neuropathy (C) is more tied to NRTIs like stavudine. Lactic acidosis (D) is rare with PIs, more common with NRTIs. It inhibits rifabutin metabolism (original E). Lopinavir's viral maturation block is potent in HIV, but its side effects, including diarrhea and lipid abnormalities, require dietary and pharmacologic management.