Keflex (Cefalexin)

Cefalexin (Keflex) is a broad‑spectrum cephalosporin antibiotic used to treat infections caused by susceptible bacteria.

• Skin and soft tissue infections: Effective in eliminating common Gram‑positive organisms causing cellulitis, impetigo and wound infections.
• Respiratory tract infections: Treats acute bronchitis, sinusitis and community‑acquired pneumonia caused by susceptible strains.
• Urinary tract infections: Eradicates Escherichia coli and other pathogens responsible for uncomplicated cystitis and pyelonephritis.

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

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: often self‑limiting, may be watery.
• Rash: non‑specific skin eruption.
• Headache: transient and mild.

Serious or Rare Side Effects

• Clostridioides difficile‑associated diarrhea: severe colitis requiring medical attention.
• Anaphylaxis: rapid onset of severe allergic reaction.
• Stevens‑Johnson syndrome: extensive skin detachment and mucosal involvement.
• Blood dyscrasias: neutropenia, thrombocytopenia, or hemolytic anemia.
• Hepatic enzyme elevation: potential liver function abnormalities.
• Renal impairment: reduced kidney function in susceptible individuals.

Before initiating therapy with Cefalexin, consider the following precautions.

• Assess renal function: adjust dose in patients with impaired clearance.
• Monitor for allergic reactions: discontinue if signs of hypersensitivity appear.
• Avoid use in patients with known cephalosporin allergy: cross‑reactivity may occur.
• Use with caution in pregnant or breastfeeding women: weigh benefits against potential risks.
• Store at room temperature: keep in the original container, protect from moisture and heat.

Cefalexin can interact with several medicines; awareness of the interaction level helps manage risk.

Major Interactions (Avoid)

• Probenecid: may increase cefalexin plasma concentrations, raising toxicity risk.
• Anticoagulants (e.g., warfarin): may enhance anticoagulant effect, requiring INR monitoring.
• Live bacterial vaccines: antibiotic therapy may reduce vaccine efficacy.

Moderate Interactions (Monitor Closely)

• Oral contraceptives: possible reduction in effectiveness; advise backup contraception.
• Diuretics (e.g., furosemide): may increase risk of nephrotoxicity.
• Aminoglycosides: additive nephrotoxic potential when used together.