Oral Conversion from IV Cefazolin
Cephalexin is the appropriate oral equivalent for IV cefazolin, typically dosed at 500 mg every 6-8 hours for adults. 1
Rationale for Cephalexin Selection
Cephalexin is a first-generation oral cephalosporin with an antimicrobial spectrum closely matching IV cefazolin, covering:
- Staphylococcus aureus (methicillin-susceptible)
- Streptococcus pneumoniae
- Streptococcus species
- Escherichia coli
- Klebsiella species
- Proteus mirabilis 2, 3
The clinical efficacy of oral cephalexin has been demonstrated as inferior to parenteral cefazolin for serious infections like pneumococcal pneumonia, making appropriate patient selection for oral conversion critical. 3
Criteria for IV-to-PO Conversion
Before converting from IV cefazolin to oral cephalexin, the patient must meet clinical stability criteria:
- Body temperature ≤37.8°C
- Heart rate ≤100 beats/min
- Respiratory rate ≤24 breaths/min
- Systolic blood pressure ≥90 mmHg
- Arterial oxygen saturation ≥90%
- Ability to maintain oral intake
- Normal mental status 2
Dosing Recommendations
Adult Dosing
- Standard dose: 500 mg orally every 6 hours 1
- Alternative: 250 mg every 6 hours for less severe infections 1
- Maximum: 4000 mg/day 1
Pediatric Dosing
- 25-50 mg/kg/day divided into 3-4 doses 4
- For more severe infections: up to 90 mg/kg/day divided into 2-3 doses 2
Clinical Context Considerations
Oral conversion is NOT appropriate for:
- Severe systemic infections requiring sustained high tissue concentrations
- Endocarditis or bacteremia
- Deep tissue infections
- Patients unable to tolerate oral medications
- Infections with organisms requiring higher drug concentrations 2, 3
Oral conversion IS appropriate for:
- Skin and soft tissue infections showing clinical improvement
- Uncomplicated urinary tract infections
- Step-down therapy after initial IV treatment with documented clinical response
- Outpatient completion of therapy 2, 5
Alternative Oral Options
If cephalexin is unavailable or contraindicated:
- Amoxicillin 500 mg every 8 hours for susceptible organisms 2
- Amoxicillin-clavulanate 875/125 mg twice daily for broader coverage including beta-lactamase producers 4
Common Pitfalls to Avoid
- Do not convert to oral therapy prematurely before achieving clinical stability, as this increases risk of treatment failure 2
- Do not assume equivalent efficacy between IV and oral routes for serious infections—oral agents achieve lower peak concentrations 3
- Do not use cephalexin for MRSA coverage—it is only effective against methicillin-susceptible staphylococci 2
- Verify adequate oral absorption—patients with gastrointestinal dysfunction may not achieve therapeutic levels 1