What broad‑spectrum antibiotic is appropriate empirically for an adult with community‑acquired pneumonia (CAP) and urinary‑tract infection (UTI) who has no drug allergies, normal renal and hepatic function, is not pregnant, and has not recently received a quinolone?

Broad-Spectrum Antibiotic for Pneumonia and UTI

For an adult with both community-acquired pneumonia and urinary tract infection, levofloxacin 750 mg orally once daily for 5–7 days provides comprehensive coverage of respiratory pathogens (including Streptococcus pneumoniae, Haemophilus influenzae, atypical organisms) and common uropathogens (E. coli, Klebsiella), making it the single most practical broad-spectrum option when treating both infections simultaneously.

Rationale for Levofloxacin Selection

• Respiratory fluoroquinolones (levofloxacin, moxifloxacin) are guideline-recommended alternatives for community-acquired pneumonia in patients with comorbidities or when β-lactam/macrolide combinations are contraindicated, with strong evidence supporting their efficacy. 1
• Levofloxacin 750 mg daily achieves clinical and bacteriologic success rates of approximately 95% in CAP, including infections caused by multidrug-resistant S. pneumoniae (MDRSP), and is FDA-approved for this indication. 2
• Levofloxacin maintains activity against >98% of S. pneumoniae isolates, including penicillin-resistant strains with MIC ≥4 mg/L, ensuring reliable pneumococcal coverage. 1
• The same agent effectively treats uncomplicated and complicated UTIs, covering the predominant uropathogens (E. coli, Klebsiella, Proteus) and eliminating the need for separate antibiotic regimens. 22

Dosing and Duration

• Administer levofloxacin 750 mg orally once daily for 5–7 days for uncomplicated CAP; this high-dose short-course regimen demonstrates equivalent efficacy to 10-day courses of 500 mg daily. 12
• For concurrent UTI, the same 5–7 day course is sufficient for uncomplicated cystitis or pyelonephritis, simplifying the treatment plan. 3
• No renal or hepatic dose adjustment is required unless creatinine clearance falls below 50 mL/min, at which point dosing should be modified per FDA labeling. 2

Coverage Spectrum

Respiratory Pathogens

• Typical bacteria: S. pneumoniae (including MDRSP), H. influenzae, Moraxella catarrhalis, Klebsiella pneumoniae. 22
• Atypical organisms: Mycoplasma pneumoniae (96% success), Chlamydophila pneumoniae, Legionella pneumophila (70% success in severe cases). 12

Urinary Pathogens

• Gram-negative uropathogens: E. coli, Klebsiella pneumoniae, Proteus mirabilis, Enterobacter species. 22
• Gram-positive organisms: Enterococcus faecalis, Staphylococcus saprophyticus. 2

When Levofloxacin Is Preferred Over Combination Therapy

• Patients with β-lactam allergies cannot receive ceftriaxone-based regimens; levofloxacin becomes the guideline-recommended alternative. 1
• Outpatients with comorbidities (COPD, diabetes, chronic organ disease) who require broader empiric coverage than amoxicillin alone. 1
• Hospitalized non-ICU patients where respiratory fluoroquinolone monotherapy is equally effective as β-lactam + macrolide combinations, with fewer clinical failures and treatment discontinuations in systematic reviews. 1
• Situations requiring a single agent to treat both pneumonia and UTI simultaneously, avoiding polypharmacy and drug interactions. 24

Important Limitations and Cautions

• Fluoroquinolones carry FDA black-box warnings for tendon rupture, peripheral neuropathy, aortic dissection, and CNS effects; reserve for patients where benefits outweigh risks. 1
• Avoid in previously healthy young adults with uncomplicated CAP where amoxicillin or doxycycline is safer and equally effective; fluoroquinolones should not be first-line in this population. 1
• Do not use in ICU-level severe pneumonia as monotherapy; combination therapy (β-lactam + macrolide or fluoroquinolone) is mandatory and reduces mortality. 15
• Quinolone resistance is rising; indiscriminate use accelerates resistance development, so restrict to appropriate clinical scenarios. 14
• Macrolide resistance among S. pneumoniae is 20–30% in most U.S. regions, making macrolide monotherapy unsafe; levofloxacin avoids this resistance pattern. 1

Alternative Regimens When Levofloxacin Is Contraindicated

For Pneumonia Alone (No UTI)

• Outpatient with comorbidities: Amoxicillin-clavulanate 875/125 mg twice daily plus azithromycin 500 mg day 1, then 250 mg daily for 5–7 days. 1
• Hospitalized non-ICU: Ceftriaxone 1–2 g IV daily plus azithromycin 500 mg IV daily, transitioning to oral when stable. 15

For UTI Alone (No Pneumonia)

• Uncomplicated cystitis: Trimethoprim-sulfamethoxazole (if local resistance <20%) or nitrofurantoin for 3–5 days. 34
• Pyelonephritis: Ceftriaxone 1–2 g IV daily transitioning to oral cephalosporin for total 7 days. 3

Monitoring and Follow-Up

• Assess clinical response at 48–72 hours; if no improvement, consider complications (pleural effusion, resistant organisms) or alternative diagnoses. 1
• For outpatients, arrange clinical review at 48 hours to evaluate symptom resolution, oral intake, and treatment adherence. 1
• Routine follow-up at 6 weeks for all patients; chest radiograph only if symptoms persist or high risk for underlying malignancy (smokers >50 years). 1
• Monitor for fluoroquinolone-associated adverse events: tendon pain, neuropathy, CNS symptoms, QTc prolongation. 1

Critical Pitfalls to Avoid

• Never delay antibiotic administration while awaiting cultures; obtain specimens promptly but start therapy immediately, as delays >8 hours increase 30-day mortality by 20–30%. 15
• Do not use levofloxacin as first-line in previously healthy young adults with uncomplicated CAP; amoxicillin or doxycycline is safer and equally effective. 1
• Avoid fluoroquinolone monotherapy in ICU patients; combination therapy is mandatory and reduces mortality in severe pneumonia. 15
• Do not assume all UTIs require 7–14 days of therapy; shorter courses (3–5 days for cystitis, 7 days for pyelonephritis) are equally effective and reduce resistance. 3
• Recognize that quinolone prescribing is influenced by nonclinical factors (physician prescribing habits, patient preferences); adhere to evidence-based indications to control resistance. 4