Introduction to Keflex (Cephalexin)
Keflex, known generically as cephalexin, is an oral antibiotic from the first-generation cephalosporin class. Introduced in 1969, it's widely used for common bacterial infections in adults and children over one year old. Cephalexin combats bacteria by targeting their cell walls, making it useful for respiratory, skin, soft tissue, and genitourinary tract infections. It's crucial to use cephalexin only for bacterial infections, as it's ineffective against viruses and contributes to antibiotic resistance if misused.
How Keflex Works: The Mechanism of Action
Keflex is a bactericidal antibiotic that kills bacteria by disrupting the synthesis of their cell walls. Its beta-lactam ring structure binds to penicillin-binding proteins (PBPs) in the bacterial cell wall, which are vital for forming the peptidoglycan layer. This interference weakens the cell wall, causing the bacterium to lyse and die. This process specifically targets bacteria without affecting human cells.
What Bacteria Does Keflex Cover? The Spectrum of Activity
As a first-generation cephalosporin, Keflex is primarily effective against gram-positive bacteria, with limited activity against certain gram-negative types.
Gram-Positive Coverage
Keflex provides good coverage against several gram-positive bacteria, including penicillinase-producing Staphylococcus aureus (but not MRSA) and penicillin-susceptible Streptococcus pneumoniae. It is also active against Streptococcus pyogenes.
Gram-Negative Coverage
Keflex's gram-negative coverage is more limited but includes bacteria frequently involved in UTIs, such as Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis. It also covers Haemophilus influenzae and Moraxella catarrhalis.
Bacteria Not Covered by Keflex
Keflex is not effective against MRSA, most enterococci, Pseudomonas, Enterobacter, and Morganella morganii species.
Common Infections Treated with Keflex
Keflex is approved and used for several infections, including skin and soft tissue infections from susceptible Staphylococcus aureus and Streptococcus pyogenes. It also treats respiratory tract infections like pharyngitis from Streptococcus pyogenes and pneumonia from Streptococcus pneumoniae. Other uses include otitis media caused by S. pneumoniae, H. influenzae, S. aureus, S. pyogenes, and M. catarrhalis, genitourinary tract infections (e.g., cystitis, prostatitis) from E. coli, P. mirabilis, and K. pneumoniae, and bone infections from S. aureus and/or P. mirabilis.
Comparison Table: Keflex vs. Amoxicillin
Both Keflex and Amoxicillin are beta-lactam antibiotics, but they differ in class and coverage.
| Feature | Keflex (Cephalexin) | Amoxicillin |
|---|---|---|
| Antibiotic Class | First-Generation Cephalosporin | Penicillin |
| Primary Coverage | Excellent against Gram-positive cocci like Staphylococcus and Streptococcus. | Broad coverage including Streptococcus, Haemophilus influenzae. |
| Staph Coverage | Generally more reliable against penicillinase-producing Staphylococcus aureus. | Often requires combination with a beta-lactamase inhibitor (e.g., clavulanate) for Staph coverage. |
| Common Uses | Skin infections, UTIs, bone infections. | Ear, nose, and throat infections (e.g., strep throat, otitis media). |
| Penicillin Allergy | Can sometimes be used in patients with a mild penicillin allergy, but cross-reactivity can occur (up to 10%). | Contraindicated in patients with a penicillin allergy. |
Conclusion
Keflex (cephalexin) remains a valuable antibiotic, particularly effective against common gram-positive bacteria and specific gram-negative pathogens, making it useful for skin, respiratory, and urinary tract infections. However, its ineffectiveness against organisms like MRSA, Pseudomonas, and Enterococcus highlights the need for careful use. Clinicians should consider local resistance patterns and use culture results when available to ensure appropriate use and preserve its effectiveness.
For further details, consult the official FDA prescribing information: KEFLEX® (cephalexin) Capsules, USP
