Keflex (Cefalexin)

Cefalexin is indicated for infections caused by susceptible bacteria, primarily affecting the skin, urinary tract and respiratory system.

• Skin and soft‑tissue infections: resolves cellulitis, impetigo and wound infections.
• Urinary tract infections: eradicates uncomplicated cystitis caused by susceptible strains.
• Respiratory tract infections: treats streptococcal pharyngitis, otitis media and community‑acquired pneumonia.
• Bone and joint infections: assists in managing osteomyelitis when appropriate.
• Surgical prophylaxis: reduces risk of postoperative bacterial contamination.

• Cefalexin inhibits bacterial cell‑wall synthesis by binding to penicillin‑binding proteins, which blocks the cross‑linking of peptidoglycan strands. This disruption weakens the cell wall, leading to osmotic instability and bacterial lysis, particularly in actively dividing Gram‑positive organisms and some Gram‑negative species.

Cefalexin may cause a range of adverse reactions, most of which are mild and reversible.

Common Side Effects

• Nausea: mild to moderate stomach upset.
• Diarrhea: loose stools, sometimes watery.
• Abdominal pain: cramping or discomfort.
• Vomiting: occasional emesis.
• Rash: mild skin redness or itching.
• Headache: transient head pain.

Serious or Rare Side Effects

• Clostridioides difficile colitis: severe diarrhea with abdominal pain.
• Anaphylaxis: rapid onset of swelling, breathing difficulty, and hypotension.
• Stevens‑Johnson syndrome: extensive skin blistering and mucosal involvement.
• Blood dyscrasias: neutropenia, thrombocytopenia, or hemolytic anemia.
• Hepatic enzyme elevation: abnormal liver function tests.
• Severe skin reactions: toxic epidermal necrolysis.

Cefalexin should be used with caution, observing several safety measures.

• Allergy assessment: confirm no known hypersensitivity to cephalosporins or penicillins.
• Renal function monitoring: adjust dose in patients with impaired kidney function.
• Hepatic impairment: use cautiously in patients with liver disease.
• Concomitant medications: review for potential interactions that may affect efficacy or safety.
• Elderly patients: consider lower initial doses due to altered pharmacokinetics.
• Store at room temperature: keep in the original container, protect from moisture and direct sunlight.

Cefalexin can affect or be affected by several medicines, requiring attention to avoid reduced effectiveness or increased toxicity.

Major Interactions (Avoid)

• Warfarin: may increase anticoagulant effect and risk of bleeding.
• Oral contraceptives: may reduce hormonal efficacy, increasing pregnancy risk.
• Probenecid: can raise cefalexin plasma concentrations, heightening side‑effect potential.

Moderate Interactions (Monitor Closely)

• Antacids containing aluminum or magnesium: may decrease cefalexin absorption; separate dosing by at least 2 hours.
• Diuretics: may enhance renal clearance, potentially lowering drug levels.
• Metformin: rare reports of lactic acidosis; monitor renal function and glycemic control.