What antibiotics are typically prescribed for common bacterial infections?

Antibiotics for Common Bacterial Infections

Urinary Tract Infections (Uncomplicated Cystitis)

For uncomplicated bacterial cystitis in adult women, prescribe nitrofurantoin 100 mg twice daily for 5 days as first-line therapy. 1

• Nitrofurantoin 5-day course is the preferred first-line agent, balancing efficacy with minimal antibiotic exposure and resistance development 1
• Alternative first-line options include fosfomycin 3g single dose or pivmecillinam 5-day course 2
• Trimethoprim-sulfamethoxazole (TMP-SMX) 160-800 mg twice daily for 3 days is second-line due to high resistance rates in many communities, but remains effective when local susceptibility is >80% 3, 2
• Fluoroquinolones (ciprofloxacin, levofloxacin) should be reserved for complicated infections or when other options are unsuitable due to resistance concerns 2

Common pitfall: Prescribing longer courses than necessary increases adverse effects without improving outcomes 1

Pyelonephritis (Complicated UTI)

• Ciprofloxacin 500-750 mg twice daily for 7 days when susceptibility is documented 3
• TMP-SMX 160-800 mg twice daily for 7 days is effective for susceptible E. coli strains 3
• For severe cases requiring hospitalization, initiate IV therapy with ceftriaxone 1-2g daily or fluoroquinolones, then transition to oral therapy based on culture results 2

Skin and Soft Tissue Infections (Cellulitis)

For nonpurulent cellulitis without MRSA risk factors, prescribe cephalexin 500 mg three times daily for 5-6 days. 3

Non-purulent cellulitis (streptococcal):

• Cephalexin 500 mg three times daily or cefazolin 1g IV every 8 hours for 5-6 days 3
• Penicillin VK 500 mg four times daily or benzylpenicillin IV are equally effective 3
• Clindamycin 300 mg three times daily for penicillin-allergic patients 3

MRSA-suspected cellulitis (purulent or risk factors present):

• Oral options: TMP-SMX 160-800 mg twice daily, doxycycline 100 mg twice daily, or linezolid 600 mg twice daily for 7-14 days 3
• IV options for severe infections: Vancomycin 15-20 mg/kg every 8-12 hours, daptomycin 10 mg/kg daily, or linezolid 600 mg twice daily 3
• Tedizolid 200 mg daily (6 days) is non-inferior to linezolid 10-day courses 3

Critical consideration: MRSA coverage is unnecessary for typical nonpurulent cellulitis unless specific risk factors exist (injection drug use, nasal MRSA colonization, penetrating trauma) 3

Respiratory Tract Infections

Community-Acquired Pneumonia:

• Amoxicillin 500-1000 mg three times daily for 5-7 days for outpatient pneumonia without comorbidities 3
• Add azithromycin 500 mg day 1, then 250 mg daily for 4 days if atypical coverage needed 3
• Levofloxacin 750 mg daily for 5 days as monotherapy alternative 3

Acute Sinusitis:

• Amoxicillin-clavulanate 875-125 mg twice daily for 5-7 days for bacterial sinusitis 3
• Doxycycline 100 mg twice daily or levofloxacin 750 mg daily for penicillin allergy 3

Acute Otitis Media:

• Amoxicillin 500-1000 mg twice daily for 5-7 days (children: 80-90 mg/kg/day divided) 3
• Amoxicillin-clavulanate for treatment failure or recent antibiotic exposure 3

Intra-Abdominal Infections

Mild to moderate community-acquired:

• Amoxicillin-clavulanate 875-125 mg twice daily 3
• Ciprofloxacin 500-750 mg twice daily plus metronidazole 500 mg three times daily 3
• Ceftriaxone 1-2g daily plus metronidazole 500 mg three times daily 3

Severe infections:

• Piperacillin-tazobactam 3.375g IV every 6 hours or 4.5g every 8 hours 3
• Ceftriaxone 1-2g daily plus metronidazole 500 mg IV every 8 hours 3
• Meropenem 1g IV every 8 hours for critically ill or suspected resistant organisms 3

Bite Wounds

Animal bites:

• Amoxicillin-clavulanate 875-125 mg twice daily for 5-7 days 3
• Doxycycline 100 mg twice daily plus metronidazole 500 mg four times daily for penicillin allergy 3

Human bites:

• Amoxicillin-clavulanate 875-125 mg twice daily 3
• Moxifloxacin 400 mg daily or ceftriaxone 1g daily for severe infections 3

Immunocompromised Patients

Aggressive and prolonged antimicrobial therapy with early combination treatment is essential for immunodeficient patients. 3

Prophylaxis regimens for bacterial respiratory infections:

• Amoxicillin 500-1000 mg daily or twice daily 3
• TMP-SMX 160 mg daily or twice daily 3
• Azithromycin 500 mg weekly or 250 mg every other day 3

Critical warning: Standard antibiotic doses and durations are often inadequate in immunocompromised hosts; consider prolonged courses and combination therapy 3

Key Principles

• Duration matters: Shorter courses (5-7 days) are equally effective as longer courses for most common infections while reducing resistance and adverse effects 3, 4
• Avoid fluoroquinolones as first-line except for specific indications due to resistance concerns and adverse effect profile 3, 2
• Culture-directed therapy: Obtain cultures for complicated infections and adjust antibiotics based on susceptibility results 2
• Clinical stability criteria: Switch from IV to oral therapy when fever resolves, patient tolerates oral intake, and clinical improvement is evident 3