Cephalexin is a commonly prescribed oral antibiotic used to treat various bacterial infections throughout the body. It belongs to the cephalosporin family of antimicrobial drugs, which are widely recognized for their effectiveness and favorable safety profile. The drug works by actively neutralizing the bacteria responsible for causing illness.
Defining the Drug Class
Cephalexin is classified as a first-generation cephalosporin antibiotic, a group of drugs that shares a structural similarity with penicillin. This class of antibiotics originated from a fungus called Acremonium, formerly known as Cephalosporium, which was discovered in the mid-20th century.
First-generation cephalosporins are generally most effective against Gram-positive bacteria, which have a single, thick cell wall structure. Cephalexin is highly effective against common Gram-positive organisms like Staphylococcus and Streptococcus species. Later generations of cephalosporins were developed to target a broader range of Gram-negative bacteria, which possess a more complex, multi-layered cell structure.
Stopping Bacterial Cell Walls: The Mechanism of Action
Cephalexin functions as a bactericidal agent, meaning it actively kills the bacterial cells rather than simply slowing their growth. Its method of attack is focused entirely on the bacterial cell wall, a rigid outer layer that provides structural integrity and protection. This cell wall is made of a mesh-like polymer called peptidoglycan, which is constantly being built and repaired by the bacteria.
The drug works by interfering with the final step of this peptidoglycan synthesis. It accomplishes this by targeting enzymes known as Penicillin-Binding Proteins (PBPs), which are essential transpeptidases responsible for cross-linking the peptidoglycan chains. Cephalexin binds to the active site of these PBPs, permanently inactivating them. This disruption prevents the necessary cross-linking, causing the cell wall to become structurally weak and defective. The weakened wall can no longer withstand the internal pressure of the bacterial cell, leading to rupture and subsequent cell death through a process called osmotic lysis.
Treating Common Infections: Clinical Applications
Cephalexin is a frequently chosen oral treatment for numerous common infections. It is widely used for skin and soft tissue infections, such as cellulitis, impetigo, and abscesses, often caused by Staphylococcus aureus and Streptococcus pyogenes. The drug’s ability to concentrate in the urinary tract also makes it a treatment option for genitourinary tract infections, including those caused by susceptible strains of E. coli and Klebsiella pneumoniae.
Cephalexin is also commonly prescribed for certain types of respiratory tract infections, including pharyngitis, or strep throat, caused by Streptococcus pyogenes. Additionally, it can be used to treat otitis media, which are middle ear infections, particularly in patients who may have a mild intolerance to penicillin. Although its main strength lies in Gram-positive coverage, it has moderate activity against select Gram-negative organisms like Proteus mirabilis. Importantly, Cephalexin is not active against certain resistant bacteria, such as Methicillin-resistant Staphylococcus aureus (MRSA), or most Enterococcus species.
Safe Usage and Potential Adverse Effects
Patients are typically advised to take Cephalexin for the full prescribed duration, even if symptoms begin to improve quickly. Stopping the medication prematurely can lead to the infection returning and potentially allow the surviving bacteria to develop resistance to the antibiotic. Cephalexin is acid-stable and rapidly absorbed, so it can be taken with or without food, though taking it with a meal can help reduce the chance of stomach upset.
The most common side effects are usually related to the gastrointestinal system and include diarrhea, nausea, vomiting, and indigestion. A more serious, yet less common, concern with nearly all antibiotics is the potential for antibiotic-associated diarrhea, which can progress to an infection by the bacterium Clostridioides difficile. Patients should seek medical attention if they experience severe or watery diarrhea, especially if it persists after the course of treatment is finished.
Patients with a known allergy to penicillin must inform their healthcare provider because there is a small risk of cross-reactivity with cephalosporins. Allergic reactions can range from mild skin rashes to severe symptoms like hives, swelling of the face or throat, and difficulty breathing. Dosage adjustments may be necessary for individuals with impaired kidney function, as the drug is primarily excreted unchanged by the kidneys.