Does Keflex Treat Staphylococcus saprophyticus?
Yes, Keflex (cephalexin) is highly effective against Staphylococcus saprophyticus and is an appropriate first-line treatment option for infections caused by this organism.
Microbiological Evidence of Susceptibility
- All 115 isolates of S. saprophyticus tested in a dedicated susceptibility study were susceptible to cephalexin, demonstrating 100% in vitro activity 1
- Cephalexin achieves urinary concentrations of 500-1000 mcg/mL following standard oral doses, which far exceeds the minimum inhibitory concentration needed to eradicate common urinary pathogens including S. saprophyticus 2
- The drug maintains full antimicrobial activity in urine and achieves adequate serum levels for systemic infections 3
Clinical Context and Dosing
For urinary tract infections caused by S. saprophyticus (the most common clinical scenario), cephalexin 500 mg orally four times daily for 7-10 days is the recommended regimen 4
- S. saprophyticus is a coagulase-negative staphylococcus that primarily causes uncomplicated urinary tract infections, particularly in young women 1
- Cephalexin is rapidly and completely absorbed from the upper intestine, with 70-100% of the dose excreted unchanged in urine within 6-8 hours 2
- The drug is essentially nontoxic at recommended doses and has a low incidence of allergic reactions due to its chemical stability 2
Alternative Agents with Equal Efficacy
- Ampicillin and trimethoprim-sulfamethoxazole also demonstrate 100% susceptibility against S. saprophyticus isolates 1
- These alternatives may be considered if cephalexin is unavailable or contraindicated 1, 5
Important Caveats
- Avoid cephalexin in patients with immediate-type penicillin hypersensitivity (urticaria, angioedema, bronchospasm, or anaphylaxis), as cross-reactivity can occur 6
- Dose reduction is required when creatinine clearance falls below 30 mL/min, proportional to the degree of renal impairment 2
- S. saprophyticus is uniformly resistant to nalidixic acid and novobiocin, which can be used as identifying characteristics but should not be used for treatment 1