Keflex (Cefalexin)

Cephalexin is indicated for bacterial infections affecting several organ systems.

• Skin and soft‑tissue infections: effective against cellulitis, impetigo and wound infections caused by susceptible bacteria.
• Respiratory tract infections: treats acute bacterial sinusitis, tonsillitis and community‑acquired pneumonia when caused by susceptible organisms.
• Urinary tract infections: used for uncomplicated cystitis and pyelonephritis caused by susceptible strains.
• Bone and joint infections: employed in osteomyelitis and septic arthritis as part of combination therapy for susceptible pathogens.

• Cephalexin exerts its antibacterial activity by binding to penicillin‑binding proteins located on the bacterial cell wall. This inhibits the final transpeptidation step of peptidoglycan synthesis, weakening the wall and leading to osmotic lysis of susceptible Gram‑positive and some Gram‑negative organisms. The drug is stable against many beta‑lactamases, allowing it to retain activity against common pathogens such as Staphylococcus aureus, Streptococcus pyogenes and certain Escherichia coli strains.

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

Common Side Effects

• Nausea: mild stomach upset often occurring after the dose.
• Diarrhea: loose stools that may be self‑limiting.
• Rash: skin redness or itching without systemic involvement.
• Headache: mild to moderate head discomfort.
• Vomiting: occasional emesis after ingestion.
• Abdominal pain: cramping or discomfort in the stomach area.

Serious or Rare Side Effects

• Anaphylaxis: severe allergic reaction with breathing difficulty and swelling.
• Clostridioides difficile‑associated colitis: severe diarrhea with possible fever.
• Stevens‑Johnson syndrome: rare skin blistering and mucosal involvement.
• Blood dyscrasias: abnormal blood counts such as neutropenia or agranulocytosis.
• Liver enzyme elevation: signs of hepatic stress detectable in labs.

Before prescribing Cephalexin, clinicians should consider several safety factors.

• Renal impairment: dose adjustment may be required in patients with reduced kidney function.
• Allergy to beta‑lactams: avoid use in individuals with known hypersensitivity to penicillins or cephalosporins.
• Pregnancy: use only if the potential benefit justifies the potential risk to the fetus.
• Concomitant anticoagulants: monitor INR or PT values as Cephalexin may enhance anticoagulant effects.
• Prolonged therapy: watch for superinfection or overgrowth of non‑susceptible organisms.
• Store at room temperature: keep in the original pack, protect from moisture and excessive heat.

Cephalexin can interact with other medicines, altering its effectiveness or safety.

Major Interactions (Avoid)

• Probenecid: increases serum Cephalexin concentrations, raising toxicity risk.
• Warfarin: may potentiate anticoagulant effect, requiring closer INR monitoring.
• Oral contraceptives: may reduce hormonal efficacy, increasing risk of unintended pregnancy.

Moderate Interactions (Monitor Closely)

• Aminoglycosides: additive nephrotoxicity potential, especially in renal‑compromised patients.
• Loop diuretics: may increase risk of renal impairment when combined.
• Allopurinol: heightened risk of rash, including severe cutaneous reactions.