What antibiotic should be prescribed for a bacterial infection?

Antibiotic Selection for Bacterial Infections

The choice of antibiotic for bacterial infections should be based on the specific infection type, suspected pathogens, and patient factors, with empiric therapy guided by local resistance patterns until culture results are available. 1

General Principles for Antibiotic Selection

• Antibiotics should only be used to treat bacterial infections, not viral infections (e.g., common cold) 2
• Complete the full course of prescribed antibiotics to prevent treatment failure and development of resistance 2
• Consider the site of infection, severity, and likely pathogens when selecting an antibiotic 1
• Take into account local resistance patterns and patient risk factors for resistant organisms 1

Skin and Soft Tissue Infections

Impetigo

• First-line: Dicloxacillin, cephalexin, clindamycin, or amoxicillin-clavulanate 1

Purulent Skin Infections (likely S. aureus)

• First-line: Dicloxacillin, cefazolin, cephalexin, clindamycin, doxycycline, or trimethoprim-sulfamethoxazole 1

MRSA Infections

• Outpatient: Trimethoprim-sulfamethoxazole, doxycycline, minocycline, or linezolid 1
• Inpatient: Vancomycin (30-60 mg/kg/day IV divided doses), linezolid (600 mg IV/PO q12h), daptomycin (4-6 mg/kg IV daily), or teicoplanin 1

Non-purulent Skin Infections

• First-line: Penicillin, clindamycin, nafcillin, cefazolin, or cephalexin 1

Necrotizing Fasciitis

• Combination therapy: Vancomycin or linezolid plus piperacillin-tazobactam or a carbapenem, or ceftriaxone plus metronidazole 1

Respiratory Tract Infections

Community-Acquired Pneumonia

• Children <3 years: Amoxicillin 80-100 mg/kg/day in three daily doses 1
• Children >3 years: Amoxicillin for suspected pneumococcal infection; macrolide for suspected atypical pathogens 1
• Adults: Amoxicillin 3g/day or broader spectrum agents (amoxicillin-clavulanate, fluoroquinolones) for patients with risk factors 1

Acute Bronchitis

• Generally viral - antibiotics not routinely recommended 1
• If bacterial infection suspected in children: Beta-lactams for <3 years; macrolides for >3 years 1

Acute Bacterial Rhinosinusitis

• First-line (mild disease, no recent antibiotics): Amoxicillin (1.5-4g/day), amoxicillin-clavulanate, cefpodoxime proxetil, cefuroxime axetil, or cefdinir 1
• For recent antibiotic use or moderate disease: Respiratory fluoroquinolones or high-dose amoxicillin-clavulanate (4g/250mg per day) 1

Diabetic Foot Infections

Mild Infections

• Oral options: Dicloxacillin, clindamycin, cephalexin, levofloxacin, amoxicillin-clavulanate 1

Moderate to Severe Infections

• Parenteral options: Levofloxacin, cefoxitin, ceftriaxone, ampicillin-sulbactam, moxifloxacin, ertapenem, imipenem-cilastatin 1
• For MRSA coverage: Linezolid, daptomycin, or vancomycin 1
• For Pseudomonas coverage: Piperacillin-tazobactam, ceftazidime, cefepime 1

Intra-abdominal Infections

Complicated Intra-abdominal Infections

• First-line: Ceftazidime-avibactam plus metronidazole, imipenem-cilastatin-relebactam, or tigecycline 1
• For carbapenem-resistant Enterobacterales: Ceftazidime-avibactam, imipenem-cilastatin-relebactam, or tigecycline plus colistin 1

Special Considerations

Beta-lactam Allergies

• For mild infections: Clindamycin, macrolides, or fluoroquinolones depending on suspected pathogen 1
• For severe infections: Fluoroquinolones, tigecycline, or linezolid depending on suspected pathogens 1

Immunocompromised Patients

• Consider broader spectrum initial therapy and longer treatment courses 1
• Prophylactic antibiotics may be indicated (e.g., trimethoprim-sulfamethoxazole for PCP) 1
• For bacterial respiratory infections: Common regimens include amoxicillin (10-20 mg/kg daily or 500-1000 mg daily for adults), trimethoprim-sulfamethoxazole, or macrolides 1

Common Pitfalls to Avoid

• Failing to adjust therapy based on culture results when available 1
• Using unnecessarily broad-spectrum antibiotics for uncomplicated infections 1
• Inadequate dosing for severe infections or resistant pathogens 1, 3
• Not considering local resistance patterns when selecting empiric therapy 1
• Insufficient duration of therapy for deep-seated infections 1
• Not reassessing therapy after 48-72 hours to evaluate clinical response 1

Specific Antibiotic Recommendations for Common Infections

• For community-acquired respiratory infections: Amoxicillin-clavulanate remains highly effective against common respiratory pathogens including beta-lactamase producing H. influenzae and M. catarrhalis 3, 4
• For acute exacerbations of chronic bronchitis: A 5-day course of high-dose amoxicillin-clavulanate (2000/125 mg twice daily) is as effective as a 7-day course of conventional dosing 5
• For resistant S. pneumoniae infections: High-dose amoxicillin or amoxicillin-clavulanate formulations provide better coverage 3, 6

Remember that antibiotic selection should be reassessed after obtaining culture results, and therapy should be narrowed when possible to reduce the risk of resistance development 2, 3.