From the Guidelines
Cephalexin is effective against most gram-positive cocci, including Streptococcus and methicillin-sensitive Staphylococcus aureus (MSSA), making it a suitable choice for many skin and soft tissue infections, as recommended by the Infectious Diseases Society of America guidelines 1. For adults, the typical dosage is 250-500 mg taken orally every 6 hours, or 500-1000 mg every 12 hours, for 7-14 days depending on the severity and type of infection. For children, the dosage is usually 25-50 mg/kg/day divided into 2-4 doses, as outlined in the guidelines 1. Some key points to consider when prescribing cephalexin include:
- It is a first-generation cephalosporin with good gram-positive coverage, including Streptococcus and MSSA 1.
- It does not cover methicillin-resistant Staphylococcus aureus (MRSA) or enterococci, and alternative antibiotics such as vancomycin or linezolid may be necessary in these cases 1.
- The drug works by inhibiting bacterial cell wall synthesis, leading to cell lysis and death.
- Potential allergic reactions in patients with penicillin allergies due to cross-reactivity should be considered, and patients should be advised to complete the full course of antibiotics to prevent resistance development. The most recent guidelines from the WHO Expert Committee in 2021 list cefalexin as a first-choice antibiotic for mild skin and soft tissue infections, further supporting its use in these cases 1.
From the FDA Drug Label
Cephalexin has been shown to be active against most strains of the following microorganisms both in vitro and in clinical infections as described in the INDICATIONS AND USAGE section Aerobes, Gram-positive: Staphylococcus aureus (including penicillinase-producing strains) Streptococcus pneumoniae (penicillin-susceptible strains) Streptococcus pyogenes Note—Methicillin-resistant staphylococci and most strains of enterococci (Enterococcus faecalis [formerly Streptococcus faecalis]) are resistant to cephalosporins, including cephalexin.
Cephalexin has coverage against certain Gram-Positive Cocci, including:
- Staphylococcus aureus (including penicillinase-producing strains)
- Streptococcus pneumoniae (penicillin-susceptible strains)
- Streptococcus pyogenes However, it is not effective against:
- Methicillin-resistant staphylococci
- Most strains of enterococci (Enterococcus faecalis) 2
From the Research
Coverage of Cephalexin against Gram-Positive Cocci
- Cephalexin is active against Gram-positive cocci, including penicillinase-producing staphylococci 3
- The antibiotic shows good activity against Staphylococcus aureus, with more than 49.1% of strains suppressed by cephalexin at concentrations of 3.13 μg/ml or less 4
- Cephalexin also exhibits activity against other Gram-positive cocci, such as Streptococcus faecalis, Streptococcus alpha, and Streptococcus mutans, although its effectiveness against the latter is limited, with only 30% of strains being sensitive 5
- The antibiotic's activity against Gram-positive bacteria is comparable to that of other cephalosporins, such as cephradine, with maximal activity observed at concentrations of 8-16 μg/ml 6
Specific Gram-Positive Cocci Coverage
- Staphylococcus aureus: cephalexin is active against this species, with a significant portion of strains being suppressed at concentrations of 3.13 μg/ml or less 4
- Streptococcus faecalis: cephalexin shows good activity against this species 5
- Streptococcus alpha: cephalexin is effective against this species, with successful treatment of sepsis cases caused by Streptococcus alpha 5
- Streptococcus mutans: cephalexin's activity against this species is limited, with only 30% of strains being sensitive 5
- Enterococci: cephalosporins, including cephalexin, possess limited activity against Enterococci 4