Sulfonamides and Trimethoprim

A 42-year-old man with HIV (CD4 count 85 cells/μL) presents with fever, dyspnea, and nonproductive cough for 1 week. Chest X-ray shows bilateral interstitial infiltrates. Sputum induction and PCR confirm *Pneumocystis jirovecii* pneumonia (PCP). He is started on trimethoprim-sulfamethoxazole (TMP-SMX) 15–20 mg/kg/day (based on TMP component) intravenously. On day 4 of therapy, he develops a maculopapular rash, fever (39.2°C), and mild hepatic transaminitis (AST 120 U/L, ALT 140 U/L). What is the most appropriate management?

Trimethoprim exerts its antimicrobial effect by inhibiting which enzyme in the bacterial folate synthesis pathway?

A 28-year-old woman presents with dysuria, frequency, and urgency for 3 days. She has no fever or flank pain. Urine dipstick shows nitrites and leukocyte esterase positive. She is allergic to penicillin (rash). Urine culture is pending. Which of the following is the most appropriate empirical antimicrobial choice for uncomplicated acute cystitis in this patient?