Keflex (Cefalexin)

Cephalexin is indicated for bacterial infections affecting several organ systems.

• Skin and soft tissue infections: effective in treating cellulitis, impetigo and wound infections caused by susceptible bacteria.
• Upper respiratory tract infections: used for acute bacterial sinusitis, tonsillitis and otitis media.
• Urinary tract infections: treats uncomplicated cystitis caused by susceptible organisms.
• Bone and joint infections: employed as part of therapy for osteomyelitis and septic arthritis.

• Cephalexin exerts its antibacterial activity by binding to penicillin‑binding proteins located on the bacterial cell wall. This binding inhibits the final transpeptidation step of peptidoglycan synthesis, weakening the cell wall and leading to osmotic lysis of susceptible Gram‑positive and some Gram‑negative bacteria. The drug is time‑dependent, and its efficacy correlates with the duration that concentrations exceed the minimum inhibitory concentration (MIC) for the target organism.

Cephalexin may cause a range of adverse reactions, most of which are mild, reversible, and dose‑independent.

Common Side Effects

• Nausea: mild stomach upset often occurring early in therapy.
• Diarrhea: loose stools, sometimes due to alteration of gut flora.
• Abdominal pain: cramping or discomfort in the stomach area.
• Rash: mild skin redness or itching.
• Vomiting: expulsion of stomach contents, usually mild.
• Headache: mild to moderate head pain.

Serious or Rare Side Effects

• Anaphylaxis: severe allergic reaction with difficulty breathing and swelling.
• Stevens‑Johnson syndrome: rare severe skin and mucous membrane disorder.
• Clostridioides difficile colitis: severe inflammation of the colon.
• Hematologic abnormalities: such as neutropenia or eosinophilia.

Before prescribing or dispensing Cephalexin, consider the following precautions to ensure safe use.

• Allergy assessment: verify no known hypersensitivity to cephalosporins or penicillins.
• Renal function: adjust dose in patients with impaired kidney function.
• Gastrointestinal history: use caution in patients with a history of colitis.
• Pregnancy and lactation: weigh potential risks as safety data are limited.
• Drug interactions: review concomitant medications for possible interactions.
• Store at ambient temperature: keep below 25°C in the original container, protect from moisture.

Cephalexin can interact with several medicines; awareness of major and moderate interactions helps avoid therapeutic problems.

Major Interactions (Avoid)

• Probenecid: reduces renal excretion, increasing cephalexin levels and toxicity risk.
• Anticoagulants (warfarin): may enhance anticoagulant effect, requiring INR monitoring.

Moderate Interactions (Monitor Closely)

• Oral contraceptives: may decrease effectiveness, advise additional contraceptive methods.
• Metformin: potential for increased plasma concentrations, monitor renal function.
• Aminoglycosides: additive nephrotoxicity risk, monitor kidney parameters.
• Tetracyclines: antagonistic effect reducing antibacterial activity.