The following infections have been paired with appropriate antibacterial therapy:

Correct Answer: A

Rationale: Acute otitis media paired with amoxicillin (A) is correct because amoxicillin is a first-line therapy for this condition, commonly caused by Streptococcus pneumoniae and Haemophilus influenzae. Its broad-spectrum activity, favorable pharmacokinetics, and safety in children make it ideal. Acute epiglottitis with cefotaxime/ceftriaxone or chloramphenicol (B) is appropriate for Haemophilus influenzae type b infections, requiring urgent treatment. Legionnaire's disease with erythromycin and rifampicin (C) is a standard combination for severe Legionella pneumophila cases, leveraging erythromycin's efficacy against atypical pathogens. Acute cystitis with trimethoprim (D) is suitable for uncomplicated, community-acquired cases caused by Escherichia coli. Although antibiotic-associated pseudomembranous colitis with oral vancomycin (original E) is also correct for Clostridioides difficile, A is selected as a representative correct pairing. These matches align with clinical guidelines, ensuring effective pathogen coverage and patient outcomes.

Correct Answer: A

Rationale: Isoniazid undergoes acetylation by N-acetyltransferase in the liver (A), a polymorphic process affecting its metabolism (fast vs. slow acetylators), influencing toxicity and dosing. It's used throughout the six-month TB regimen in the UK (initial 2 months with rifampicin, pyrazinamide, ethambutol, then 4 months with rifampicin), not just initially (B is incorrect). It's readily absorbed from the gut (C), achieving high bioavailability. It diffuses into the CSF (D is incorrect), critical for TB meningitis treatment. It's not contraindicated in children under 10 (original E). Isoniazid's bactericidal action on Mycobacterium tuberculosis, targeting mycolic acid synthesis, is foundational in TB therapy, though peripheral neuropathy (preventable with pyridoxine) is a key side effect.

Correct Answer: B

Rationale: Voriconazole is active against Aspergillus (B), making it a first-line treatment for invasive aspergillosis due to its potent inhibition of ergosterol synthesis via CYP51, with high efficacy against this mold. It's available and effective orally and IV (A), offering flexibility in severe infections. It inhibits cortisol biosynthesis (C), potentially causing adrenal suppression, a rare but notable effect. It inhibits CYP3A (D), leading to significant drug interactions (e.g., with cyclosporine). GI absorption isn't reduced by omeprazole (original E is incorrect). Voriconazole's broad antifungal spectrum, including Candida and Fusarium, and its bioavailability make it critical in immunocompromised patients, though visual disturbances and hepatotoxicity require monitoring.

Correct Answer: D

Rationale: Lymphopenia (D) is an adverse effect of interferons, like interferon alfa, due to bone marrow suppression, reducing lymphocyte counts, common in chronic hepatitis or cancer therapy. Hypocalcemia (A) isn't typical; interferons more often cause flu-like symptoms. Inhibition of spermatogenesis (B) occurs, reflecting gonadal toxicity, but D is highlighted. Renal tubular acidosis (C) isn't a primary effect; nephrotoxicity is rare. Flu-like symptoms (original E) are frequent, including fever and fatigue. Interferons' immunomodulatory and antiproliferative actions explain these effects, activating immune responses while suppressing cell proliferation, necessitating monitoring during prolonged use.

Correct Answer: B

Rationale: Giardia lamblia paired with metronidazole (B) is correct, a first-line treatment for giardiasis, targeting anaerobic protozoa via DNA disruption, with high cure rates. Trypanosoma gambiense with pentamidine and suramin (A) is partially correct; pentamidine or suramin alone is used early, not combined. Taenia saginata with emetine (C) is wrong; praziquantel or niclosamide is standard. Strongyloides with mebendazole (D) is incorrect; ivermectin is preferred. Toxocara canis with pyraquantel (original E) is wrong; albendazole is used. Metronidazole's efficacy in Giardia, amoebiasis, and trichomoniasis reflects its selective anaerobic action, though GI side effects and alcohol intolerance are notable.