Overview
Cefalexin is a widely used, first-generation cephalosporin antibiotic. It is highly valued for its excellent oral absorption and robust efficacy against Gram-positive bacteria, particularly staphylococci and streptococci. It is a cornerstone treatment for uncomplicated skin and soft tissue infections, as well as straightforward urinary tract infections.

Mechanism of Action
As a bactericidal antibiotic, cefalexin actively kills susceptible bacteria. It achieves this by binding to specific penicillin-binding proteins (PBPs) located inside the bacterial cell wall. This binding effectively halts the final stages of peptidoglycan synthesis, which is crucial for cell wall strength. The weakened cell wall eventually ruptures due to osmotic pressure, destroying the bacteria.

Dosage and Administration
The standard adult dosage is typically 250 mg to 500 mg administered every 6 hours, or 500 mg every 12 hours, depending on the severity of the infection. The usual duration of treatment is 7 to 14 days. It can be taken on an empty stomach or with food, though taking it with food may help reduce potential stomach upset.

Side Effects
Cefalexin is generally very well-tolerated. The most frequently observed side effects are mild and transient gastrointestinal issues, such as diarrhea, nausea, vomiting, and indigestion. Less commonly, patients may experience mild skin rashes or itching. Prolonged use may occasionally lead to secondary yeast infections, such as oral thrush or vaginal candidiasis.

Contraindications and Precautions
The primary contraindication is a known history of hypersensitivity to cefalexin or other cephalosporin antibiotics. Due to structural similarities, there is a small risk of cross-allergenicity in patients with severe, immediate-type allergic reactions to penicillins, so it should be used with caution in these individuals. Dosage adjustment is required in patients with significant renal impairment.

Pregnancy and Lactation
Cefalexin is considered one of the safer antibiotics to use during pregnancy and is frequently prescribed for pregnant women when appropriate. It is excreted in breast milk in small concentrations. While generally considered safe during lactation, the infant should be monitored for potential mild gastrointestinal disturbances.