When should antibiotics (abx) be started in patients with suspected bacterial infections?

Indications to Start Antibiotics in Suspected Bacterial Infections

Antibiotics should be started within 1 hour after recognition of septic shock, within 1-3 hours for bacterial meningitis, and can be delayed up to 4-6 hours for less severe infections to allow for proper diagnostic evaluation. 1

Timing Based on Infection Severity

High-Risk/Life-Threatening Infections (Immediate Treatment)

• Start antibiotics within 1 hour for patients with septic shock 1
• Administer antibiotics within 1-3 hours (ideally within 1 hour) for bacterial meningitis 1
• Provide immediate antibiotics for patients with high risk of severe illness or death from sepsis (NEWS2 score ≥7) 1
• Administer antibiotics in the community for suspected meningitis if hospital transfer will be delayed by more than 1 hour 1

Moderate-Risk Infections

• Start antibiotics within 3 hours for patients with moderate risk of severe illness or death from sepsis (NEWS2 score 5-6) 1
• Consider antibiotics within 4 hours for severe community-acquired pneumonia, but first rule out other diagnoses to avoid unnecessary prescriptions 1

Low-Risk Infections

• Administer antibiotics within 6 hours for patients with low risk of severe illness or death from sepsis 1
• Consider delaying antibiotics for 4-8 hours in less severe infectious syndromes to allow for diagnostic evaluation and more targeted therapy 2

Special Patient Populations Requiring Prompt Treatment

• Minimize time to first antibiotic dose in immunocompromised patients (asplenic, neutropenic) 1
• Provide immediate antibiotics for life-threatening infections including:
  • Bacterial necrotizing cellulitis 1
  • Purpura fulminans 1
  • Post-splenectomy fever 1
  • Neutropenic fever 1

Diagnostic Considerations Before Starting Antibiotics

• Obtain blood cultures and other relevant specimens (sputum, urine) before starting antibiotics whenever possible 1
• Perform pneumococcal and Legionella urinary antigen testing when appropriate 1
• Consider alternative diagnoses within the first 4 hours for suspected community-acquired pneumonia to avoid unnecessary antibiotic use 1
• For COVID-19 patients, use antibiotics restrictively unless there are clear signs of bacterial co-infection 1

Pitfalls and Caveats

• Delaying antibiotics for diagnostic purposes is acceptable in most cases unless septic shock or bacterial meningitis are suspected 2
• Administering pre-hospital antibiotics for meningitis should not delay transfer to hospital 1
• Avoid antibiotics in patients with known anaphylaxis to penicillins or cephalosporins until hospital admission 1
• The gap in effective antibiotic coverage is often with resistant Gram-negative organisms; consider this when selecting empiric therapy 3
• Overly aggressive time-to-antibiotic targets may promote antibiotic overuse and associated harms in patients with non-infectious conditions 4

Monitoring After Starting Antibiotics

• Re-evaluate antibiotic choice when culture results become available, switching to narrower spectrum options when possible 1
• Consider stopping antibiotics if cultures are negative after 48 hours of incubation and clinical improvement is observed 1
• For bloodstream infections, 7 days of appropriate antibiotic therapy may be sufficient for most patients rather than longer courses 5

By following these guidelines for initiating antibiotics based on infection severity and patient risk factors, clinicians can balance the need for prompt treatment in life-threatening infections while minimizing unnecessary antibiotic use in less severe cases.