Prescription ·Strong evidence ·Reviewed May 2026
A first-generation cephalosporin antibiotic with excellent activity against gram-positive cocci including methicillin-susceptible S. aureus (MSSA) and streptococci. Commonly used for skin and soft tissue infections, uncomplicated urinary tract infections, bone and joint infections, and as prophylaxis for certain dental and surgical procedures. It has limited gram-negative coverage compared to later-generation cephalosporins.
The bottom line
Evidence rating strong. Most-documented uses: treats skin and soft tissue infections (cellulitis, impetigo), treats uncomplicated urinary tract infections, treats bone and joint infections. 10 sources indexed (2016–2025), with 3 interaction records on file.
Core mechanism
Binds to penicillin-binding proteins (PBPs) in the bacterial cell wall, inhibiting the transpeptidation step of peptidoglycan synthesis. This disrupts cell wall integrity, leading to osmotic instability and bacterial cell lysis. As a first-generation cephalosporin, it is resistant to some but not all beta-lactamases.
Well absorbed orally with approximately 90% bioavailability. Food may delay absorption slightly but does not reduce total absorption. Can be taken with or without food.3
Nutrients this medication can lower over time, and what to replace.
Broad-spectrum antibiotic exposure can suppress gut bacteria that synthesize menaquinones, lowering vitamin K availability in susceptible patients.
Probiotic supplementation during cephalexin therapy reduces antibiotic-associated diarrhea and helps preserve gut microbiome diversity disrupted by cephalosporin coverage.
Recommendation: Take probiotics throughout your cephalexin course, separated by at least 2 hours from each antibiotic dose. Continue for at least 1 week after the antibiotic ends.
Saccharomyces boulardii reduces antibiotic-associated diarrhea during cephalexin therapy and is unaffected by the antibiotic because it is a yeast.
Recommendation: Take Saccharomyces boulardii throughout your cephalexin course. Timing flexibility is greater than with bacterial probiotics. Continue for at least 1 week after the antibiotic ends.
Broad-spectrum antibiotics including cephalosporins suppress vitamin K-producing gut bacteria, which can lower endogenous vitamin K2 (menaquinone) levels during prolonged courses. In patients with marginal vitamin K intake, malnutrition, or coagulopathy risk, this can increase bleeding tendency. Routine supplementation is generally not required for short courses in well-nourished adults.
Recommendation: For short cephalexin courses in healthy adults, no special action is needed. For prolonged therapy, malnourished patients, or those at bleeding risk, consider monitoring coagulation parameters and discussing vitamin K2 supplementation with your clinician.
Numbered references. Citations throughout the page link here.
Kanan M, Atif S, Mohammed F et al.. A Systematic Review on the Clinical Pharmacokinetics of Cephalexin in Healthy and Diseased Populations. Antibiotics (Basel, Switzerland). 2023
Saad AF, Goldman B, Spencer N et al.. Prophylactic Oral Cephalexin and Metronidazole Compared With Placebo After Cesarean Delivery to Reduce Infection Complications in Women With Obesity: A Randomized Controlled Trial. Obstetrics and gynecology. 2025
Yadav K, Eagles D, Perry JJ et al.. High-dose cephalexin for cellulitis: a pilot randomized controlled trial. CJEM. 2023
Rageh AH, Abdel-Rahim SA, Askal HF et al.. Hydrophilic-interaction planar chromatography in ultra-sensitive determination of α-aminocephalosporin antibiotics. Application to analysis of cefalexin in goat milk samples using modified QuEChERS extraction technique. Journal of pharmaceutical and biomedical analysis. 2019
Fonte E, Ferreira P, Guilhermino L. Temperature rise and microplastics interact with the toxicity of the antibiotic cefalexin to juveniles of the common goby (Pomatoschistus microps): Post-exposure predatory behaviour, acetylcholinesterase activity and lipid peroxidation. Aquatic toxicology (Amsterdam, Netherlands). 2016
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