Keflex (Cefalexin)

Cefalexin is a broad‑spectrum antibiotic that targets bacterial infections of several organ systems.

• Skin and soft‑tissue infections: helps eradicate common Gram‑positive organisms causing cellulitis, impetigo and wound infections.
• Respiratory tract infections: effective against streptococcal and staphylococcal pathogens in conditions such as acute bronchitis and sinusitis.
• Urinary tract infections: clears susceptible Escherichia coli and other uropathogens causing cystitis.
• Bone and joint infections: used as part of combination therapy for osteomyelitis and septic arthritis caused by susceptible bacteria.

• Cefalexin inhibits bacterial cell‑wall synthesis by binding to penicillin‑binding proteins, which prevents the cross‑linking of peptidoglycan strands. This disruption weakens the cell wall, leading to osmotic instability and bacterial lysis, primarily affecting susceptible Gram‑positive and some Gram‑negative organisms.

Cefalexin may cause a range of adverse reactions, from mild to severe.

Common Side Effects

• Nausea: mild gastrointestinal upset occurring in many patients.
• Diarrhea: loose stools that may be self‑limiting.
• Rash: skin redness or mild itching.
• Headache: transient headache without neurological signs.

Serious or Rare Side Effects

• Anaphylaxis: severe allergic reaction with breathing difficulty and swelling.
• Clostridioides difficile colitis: severe diarrhea due to intestinal flora disruption.
• Hepatotoxicity: elevated liver enzymes or jaundice in rare cases.

Before using Cefalexin, consider the following safety measures.

• Allergy assessment: avoid if the patient has a known cephalosporin or penicillin hypersensitivity.
• Renal function: adjust dose in patients with impaired kidney function.
• Pregnancy and lactation: discuss risks with a healthcare provider before use.
• Concomitant antibiotics: monitor for potential antagonistic effects.
• Store at ambient temperature: keep below 25°C, retain in original packaging, protect from moisture.

Cefalexin can interact with several medicines, requiring attention to avoid reduced efficacy or increased toxicity.

Major Interactions (Avoid)

• Probenecid: may increase cefalexin plasma concentrations, raising toxicity risk.
• Oral anticoagulants: can enhance anticoagulant effect, necessitating INR monitoring.

Moderate Interactions (Monitor Closely)

• Metformin: may increase metformin levels; monitor renal function and blood glucose.
• Oral contraceptives: potential reduction in contraceptive effectiveness; advise backup methods.
• Antacids containing aluminum or magnesium: may decrease cefalexin absorption; separate dosing by at least 2 hours.