Keflex (Cefalexin)

Cefalexin is a first‑generation cephalosporin antibiotic used to treat infections caused by susceptible bacteria.

• Skin and soft‑tissue infections: Reduces bacterial load and promotes healing of cellulitis, impetigo and wound infections.
• Respiratory tract infections: Eradicates pathogens responsible for acute bronchitis, sinusitis and community‑acquired pneumonia.
• Urinary tract infections: Clears uncomplicated cystitis and pyelonephritis caused by susceptible strains.
• Bone and joint infections: Assists in treating osteomyelitis and septic arthritis when appropriate.

• Cefalexin inhibits bacterial cell‑wall synthesis by binding to penicillin‑binding proteins (PBPs) on the bacterial membrane. This binding blocks the cross‑linking of peptidoglycan strands, weakening the cell wall and leading to osmotic instability and bacterial lysis. The action is bactericidal against a range of Gram‑positive and some Gram‑negative organisms.

Cefalexin may cause a range of adverse reactions, most of which are mild and self‑limiting.

Common Side Effects

• Nausea: mild to moderate upset stomach.
• Diarrhea: often watery, may be self‑resolving.
• Abdominal pain: cramping or discomfort.
• Rash: mild skin erythema or itching.
• Headache: transient tension‑type headache.
• Vomiting: occasional episodes.

Serious or Rare Side Effects

• Clostridioides difficile‑associated diarrhea: severe colitis requiring medical attention.
• Anaphylaxis: rapid onset of swelling, airway compromise, and hypotension.
• Stevens‑Johnson syndrome: severe mucocutaneous reactions.
• Blood dyscrasias: neutropenia, thrombocytopenia, or hemolytic anemia.
• Hepatic enzyme elevation: potential liver function abnormalities.
• Renal impairment: worsening kidney function in susceptible patients.

Before prescribing cefalexin, clinicians should consider several safety aspects.

• Assess renal function: adjust dose in patients with impaired kidney function.
• Monitor for allergic reactions: discontinue if rash, urticaria, or anaphylaxis occurs.
• Avoid use in patients with known cephalosporin hypersensitivity.
• Use with caution in pregnancy or breastfeeding: consult a physician as data are limited.
• Complete full course: to prevent bacterial resistance and relapse.
• Store at ambient temperature below 25°C: keep in the original pack, protect from moisture and light.

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

Major Interactions (Avoid)

• Probenecid: may increase cefalexin plasma levels, raising toxicity risk.
• Oral anticoagulants (e.g., warfarin): can enhance anticoagulant effect, increasing bleeding risk.
• Live bacterial vaccines: antibiotic may reduce vaccine efficacy.
• Methotrexate: concurrent use may increase methotrexate toxicity.

Moderate Interactions (Monitor Closely)

• Oral contraceptives: may reduce hormonal effectiveness, consider backup contraception.
• Diuretics (e.g., furosemide): potential increase in nephrotoxicity.
• Allopurinol: may raise the incidence of rash when combined.