What is the recommended antibiotic prescription for a patient with a bacterial infection?

Antibiotic Prescription for Bacterial Infection

For a confirmed bacterial infection, prescribe amoxicillin 500 mg orally three times daily for 7-10 days as first-line therapy for most community-acquired infections, or amoxicillin-clavulanate 875/125 mg twice daily for broader coverage when beta-lactamase-producing organisms are suspected. 1

Infection-Specific Prescribing Guidance

Skin and Soft Tissue Infections (SSTI)

For methicillin-susceptible infections:

• Dicloxacillin 500 mg orally four times daily is the oral agent of choice for adults 1
• Cephalexin 500 mg orally four times daily for penicillin-allergic patients (except immediate hypersensitivity) 1
• Pediatric dosing: Dicloxacillin 25 mg/kg/day in 4 divided doses or cephalexin 25-50 mg/kg/day in 4 divided doses 1
• Duration: 7 days depending on clinical response 1

For MRSA or purulent cellulitis:

• Clindamycin 300-450 mg orally three times daily (adults) or 10-13 mg/kg/dose every 6-8 hours (pediatric, max 40 mg/kg/day) 1
• TMP-SMX 1-2 double-strength tablets twice daily (adults) or trimethoprim 4-6 mg/kg/dose every 12 hours (pediatric) 1
• Doxycycline 100 mg twice daily (adults) or 2 mg/kg/dose every 12 hours for children <45 kg 1
• Caveat: TMP-SMX is pregnancy category C/D and contraindicated in third trimester and children <2 months; tetracyclines contraindicated in children <8 years 1

For complicated SSTI requiring IV therapy:

• Vancomycin 15-20 mg/kg/dose IV every 8-12 hours (adults) or 15 mg/kg/dose every 6 hours (pediatric) 1
• Linezolid 600 mg IV/PO twice daily (adults) or 10 mg/kg/dose every 8 hours (pediatric, max 600 mg/dose) 1

Bite Wounds

For animal bites:

• Amoxicillin-clavulanate 500/875 mg twice daily is first-line oral therapy 1
• Alternative: Doxycycline 100 mg twice daily (excellent activity against Pasteurella multocida) 1
• IV option: Ampicillin-sulbactam 1.5-3.0 g every 6-8 hours 1

For human bites:

• Amoxicillin-clavulanate 500 mg every 8 hours orally 1
• Alternative: Doxycycline 100 mg twice daily (good activity against Eikenella species, staphylococci, and anaerobes) 1

Respiratory Tract Infections

For acute bacterial sinusitis:

• Azithromycin 500 mg on day 1, then 250 mg daily for days 2-5 demonstrated 100% clinical response rate 2
• Amoxicillin 500 mg three times daily for 10 days is equally effective 2
• Azithromycin offers advantage of once-daily dosing and shorter duration 2

For lower respiratory tract infections:

• Amoxicillin 1 g three times daily for 7 days showed benefit primarily in patients with combined bacterial/viral infections (reduced illness deterioration, OR 0.24,95% CI 0.11-0.53) 3
• Limited clinically meaningful benefit in purely bacterial or viral infections 3

Urinary Tract Infections

For acute uncomplicated UTI:

• Amoxicillin 250 mg three times daily for 10 days produces 97.3% bacteriologic cure rate 4
• Alternative: Bacampicillin 400 mg twice daily for 10 days (95.8% cure rate, may improve compliance) 4

Intra-Abdominal Infections

For complicated intra-abdominal infections:

• Piperacillin-tazobactam 3.375 g IV every 6 hours 1
• Ertapenem 1 g IV every 24 hours 1
• Meropenem 1 g IV every 8 hours 1
• Duration: 4-7 days unless source control is difficult 1

For neonatal necrotizing enterocolitis:

• Ampicillin + gentamicin + metronidazole OR ampicillin + cefotaxime + metronidazole OR meropenem 1
• Add vancomycin for suspected MRSA or ampicillin-resistant enterococcal infection 1

Bacteremia and Endocarditis

For MRSA bacteremia:

• Vancomycin 15-20 mg/kg/dose IV every 8-12 hours (adults) or 15 mg/kg/dose every 6 hours (pediatric) 1
• Daptomycin 6 mg/kg/dose IV daily (adults) or 6-10 mg/kg/dose daily (pediatric) 1

For prosthetic valve endocarditis (MRSA):

• Vancomycin + gentamicin + rifampin: Vancomycin 15-20 mg/kg/dose every 8-12 hours + gentamicin 1 mg/kg/dose every 8 hours + rifampin 300 mg every 8 hours 1

Bone and Joint Infections

For osteomyelitis (MRSA):

• Vancomycin 15-20 mg/kg/dose IV every 8-12 hours (adults) or 15 mg/kg/dose every 6 hours (pediatric) 1
• Daptomycin 6 mg/kg/day IV (adults) or 6-10 mg/kg/day (pediatric) 1
• Linezolid 600 mg IV/PO twice daily (adults) or 10 mg/kg/dose every 8 hours (pediatric) 1
• Surgical debridement is mainstay of therapy 1
• Some experts recommend adding rifampin 600 mg daily or 300-450 mg twice daily 1

Critical Prescribing Considerations

Dosing Adjustments

• Renal impairment: Exercise caution with azithromycin when GFR <10 mL/min 5
• Hepatic impairment: Exercise caution with azithromycin as it is principally eliminated via liver 5
• Aminoglycosides: Base initial dosing on adjusted body weight; use serum drug-concentration monitoring 1
• Vancomycin: Base initial dosing on total body weight; consider therapeutic drug monitoring 1

Common Pitfalls to Avoid

• Do not co-administer aluminum/magnesium-containing antacids with azithromycin 5
• Monitor prothrombin time when co-administering azithromycin with oral anticoagulants (may potentiate warfarin effects) 5
• Clindamycin carries risk of C. difficile-associated disease more frequently than other oral agents 1
• Avoid fluoroquinolones in children <18 years and tetracyclines in children <8 years 1

Duration of Therapy

• Most SSTIs: 7 days depending on clinical response 1
• Complicated intra-abdominal infections: 4-7 days unless source control is difficult 1
• Bacteremia: 7-14 days 1
• Osteomyelitis/septic arthritis: Typically 4-6 weeks, longer for recurrent disease 1

Storage and Administration

• Amoxicillin suspension: Refrigeration preferable but not required; shake well before use; discard after 14 days 6
• Use calibrated oral syringe for pediatric dosing 6

Antibiotic Stewardship

• De-escalate to narrow-spectrum monotherapy when culture results available 7
• Shorten duration when clinically appropriate 7
• Lower-risk community-acquired infections: Do not alter therapy if satisfactory clinical response occurs, even if unsuspected pathogens reported 1
• High-severity infections: Use culture/susceptibility results to guide pathogen-directed therapy 1