From the Research
Intravenous (IV) cefazolin (Ancef) has 100% bioavailability, whereas oral cephalexin (Keflex) has approximately 90% bioavailability, making IV cefazolin the preferred choice for severe infections requiring immediate antibiotic presence 1. The difference in bioavailability between IV cefazolin and oral cephalexin is crucial in determining their clinical applications. IV cefazolin delivers the entire dose immediately to the systemic circulation, providing rapid peak concentrations and immediate antimicrobial activity. In contrast, cephalexin undergoes first-pass metabolism and has a slight delay in reaching therapeutic levels. This distinction is particularly important when treating severe infections, such as sepsis or septic shock, where prompt antibiotic administration is essential to reduce mortality 2, 3, 4.
Key points to consider:
- IV cefazolin is typically reserved for hospitalized patients with moderate to severe infections
- Cephalexin is suitable for less severe infections that can be managed in outpatient settings
- Both medications are first-generation cephalosporins with similar antimicrobial coverage against gram-positive organisms and some gram-negative bacteria
- The choice between IV cefazolin and oral cephalexin depends on the severity of the infection, the patient's clinical condition, and the need for immediate antibiotic presence.
In the context of sepsis or septic shock, the most recent study 1 highlights the importance of prompt antibiotic administration and the potential risks of antibiotic overtreatment. Therefore, IV cefazolin is the preferred choice for severe infections requiring immediate antibiotic presence, due to its 100% bioavailability and rapid onset of action.