How to start intravenous (IV) antibiotics?

How to Start IV Antibiotics

Administer IV antibiotics within 1 hour of recognizing sepsis or septic shock, immediately after obtaining blood cultures (if this causes no significant delay), using empiric broad-spectrum agents that cover all likely pathogens based on the suspected source and local resistance patterns. 1

Timing: The Critical First Hour

The evidence is unequivocal: each hour of delay in appropriate antimicrobial administration increases mortality by approximately 7-8% in septic patients. 1 The Surviving Sepsis Campaign guidelines provide the strongest recommendation (Grade 1B/1C) that IV antimicrobials must be initiated as soon as possible after recognition, with a target of within 1 hour for both sepsis and septic shock. 1

Risk-Stratified Timing Approach

For patients where sepsis severity is uncertain, use a risk-stratified approach: 2

• High-risk patients (NEWS2 ≥7 or clinical signs of shock): Antibiotics within 1 hour
• Moderate-risk patients (NEWS2 5-6): Antibiotics within 3 hours
• Low-risk patients: Antibiotics within 6 hours

Pre-Antibiotic Workflow

Blood Cultures First (But Don't Delay)

Obtain at least 2 sets of blood cultures (aerobic and anaerobic) before administering antibiotics, but only if this causes no delay greater than 45 minutes. 1 Draw at least one set percutaneously and one through each vascular access device (if the device has been in place >48 hours). 1

Critical pitfall to avoid: Never delay antibiotics beyond the 1-hour window while waiting for cultures. 2, 3 If venous access is difficult or cultures cannot be obtained promptly, start antibiotics immediately. 4

Establish IV Access

Secure reliable IV access immediately. 5 If IV access cannot be promptly obtained in children, the first antimicrobial dose may be given intramuscularly, orally, or rectally, though IV is strongly preferred for optimal bioavailability. 1

Selecting Empiric Antibiotics

Broad-Spectrum Coverage is Mandatory

Use empiric broad-spectrum therapy with one or more antimicrobials that cover all likely pathogens, including bacterial and potentially fungal or viral pathogens. 1 The regimen must penetrate adequately into tissues presumed to be the source of infection. 1

Key Selection Factors

Consider these critical factors when choosing antibiotics: 1, 6

• Suspected source of infection (pneumonia, urinary tract, intra-abdominal, skin/soft tissue)
• Local antimicrobial resistance patterns
• Recent antibiotic exposure (within past 90 days)
• Healthcare-associated vs. community-acquired infection
• Patient's immune status (neutropenia, HIV, immunosuppression)
• Recent hospitalization (>1 week increases resistant pathogen risk) 2

Combination Therapy for Septic Shock

For septic shock specifically, use combination empirical therapy with at least two antibiotics from different antimicrobial classes aimed at the most likely bacterial pathogens. 1, 3 This provides broader initial coverage and may improve outcomes in the most critically ill patients. However, combination therapy is NOT routinely recommended for sepsis without shock. 1

Specific Clinical Scenarios

For severe community-acquired pneumonia with ICU admission: 1

• β-lactam (ceftriaxone, cefotaxime, or ampicillin-sulbactam) PLUS azithromycin or a respiratory fluoroquinolone

For suspected Pseudomonas infection: 1

• Antipseudomonal β-lactam (piperacillin-tazobactam, cefepime, imipenem, or meropenem) PLUS ciprofloxacin or levofloxacin 750 mg, OR the β-lactam plus an aminoglycoside and azithromycin

For suspected MRSA: 1

• Add vancomycin or linezolid to the regimen

Administration Technique

Dosing Strategy

Administer antimicrobials at maximum recommended dosages during the initial phase of sepsis treatment. 1 Optimal dosing based on pharmacokinetic/pharmacodynamic principles is essential. 1

Infusion Method

Most antibiotics should be administered as intermittent IV infusions over 30 minutes. 7 However, for patients with limited vascular access or when rapid administration is critical, certain β-lactams (including cefepime and ceftriaxone) can be given as IV push/bolus. 2, 5 This can save valuable time in emergency situations.

Practical Implementation

To achieve the 1-hour target consistently: 1

• Use "STAT" orders with explicit time requirements
• Stock premixed antibiotic solutions in the emergency department for immediate availability
• Establish institutional protocols that allow nurses to draw cultures and administer antibiotics without delays
• Address supply chain issues proactively
• Optimize communication between medical, pharmacy, and nursing staff

Common pitfall: Some antimicrobials may not remain stable if premixed. Verify your institution's premixed solutions are appropriate. 1

Incompatibilities to Avoid

Do not mix cefepime with ampicillin at concentrations >40 mg/mL, and do not add to metronidazole, vancomycin, gentamicin, tobramycin, or aminophylline due to potential interactions. 7 If concurrent therapy is needed, administer these agents separately through different IV lines or at different times.

Reassessment and De-escalation

Reassess the antimicrobial regimen daily for potential de-escalation once pathogen identification and sensitivities are available. 1, 3 Narrow therapy to the most appropriate single agent as soon as the susceptibility profile is known, typically within 3-5 days. 1 This antimicrobial stewardship practice reduces resistance development and adverse effects without compromising outcomes.

Typical duration of therapy is 7-10 days, though longer courses may be necessary for slow clinical response, undrainable infection foci, S. aureus bacteremia, or immunocompromised patients. 1