Keflex (Cefalexin)

Cefalexin acts as a broad‑spectrum antibacterial agent targeting susceptible gram‑positive and some gram‑negative organisms.

• Skin and soft tissue infections: effective for 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 strains.
• Urinary tract infections: clears uncomplicated cystitis and pyelonephritis due to susceptible organisms.
• Bone and joint infections: used for osteomyelitis and septic arthritis when the pathogen is sensitive to cefalexin.

• Cefalexin inhibits bacterial cell wall synthesis by binding to penicillin‑binding proteins (PBPs) on the bacterial membrane. This binding blocks the transpeptidation step of peptidoglycan cross‑linking, weakening the cell wall and leading to osmotic lysis of susceptible bacteria.

Cefalexin is generally well tolerated, but adverse reactions can occur.

Common Side Effects

• Nausea: mild to moderate stomach upset.
• Diarrhea: often self‑limiting, may be watery.
• Abdominal pain: cramping or discomfort.
• Rash: erythematous skin eruption.
• Headache: transient mild headache.
• Taste disturbance: altered taste perception.

Serious or Rare Side Effects

• Anaphylaxis: severe allergic reaction requiring immediate medical attention.
• Clostridioides difficile‑associated diarrhea: potentially severe colitis.
• Stevens‑Johnson syndrome: rare mucocutaneous blistering disorder.
• Blood dyscrasias: neutropenia, thrombocytopenia, or hemolytic anemia.
• Hepatic enzyme elevation: abnormal liver function tests.
• Seizures: rare, especially in patients with renal impairment.

Before prescribing cefalexin, clinicians should consider several safety factors.

• Assess renal function: adjust dose in patients with impaired kidney function.
• Monitor for allergic reactions: discontinue if severe rash or anaphylaxis occurs.
• Use with caution in patients with gastrointestinal disease: may exacerbate colitis.
• Avoid use in patients with known hypersensitivity to cephalosporins or penicillins.
• Store at ambient temperature: keep in the original pack, protect from moisture and heat.

Cefalexin can interact with other medicines, influencing efficacy or safety.

Major Interactions (Avoid)

• Probenecid: increases cefalexin plasma levels, raising toxicity risk.
• Warfarin: may potentiate anticoagulant effect, requiring INR monitoring.
• Oral contraceptives: may reduce hormonal efficacy, advise backup contraception.

Moderate Interactions (Monitor Closely)

• Aminoglycosides: additive nephrotoxicity, monitor renal function.
• Loop diuretics: may increase risk of renal impairment.
• Metformin: may need dose adjustment in renal dysfunction when combined with cefalexin.