Keflex (Cefalexin)

Cefalexin is a broad‑spectrum antibiotic that targets susceptible bacterial infections in several organ systems.

• Skin and soft‑tissue infections: effective for mild to moderate cellulitis, impetigo and wound infections caused by susceptible organisms.
• Respiratory tract infections: used to treat acute bronchitis, sinusitis and community‑acquired pneumonia when indicated.
• Urinary tract infections: helps eradicate uncomplicated cystitis and pyelonephritis caused by susceptible strains.
• Bone and joint infections: employed as part of therapy for osteomyelitis and septic arthritis when bacteria are known to be cefalexin‑sensitive.

• Cefalexin inhibits bacterial cell‑wall synthesis by binding to penicillin‑binding proteins (PBPs) located on the inner surface of the bacterial 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 organisms.

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

Common Side Effects

• Diarrhea: loose stools occurring during treatment.
• Nausea: feeling of stomach upset.
• Vomiting: expulsion of stomach contents.
• Rash: mild skin redness or itching.
• Headache: transient head pain.
• Vaginal yeast infection: overgrowth of Candida species.

Serious or Rare Side Effects

• Clostridioides difficile‑associated diarrhea: severe colitis requiring medical attention.
• Anaphylaxis: life‑threatening allergic reaction with airway compromise.
• Stevens‑Johnson syndrome: severe skin and mucous membrane disorder.
• Hemolytic anemia: destruction of red blood cells.
• Elevated liver enzymes: indication of hepatic stress.
• Kidney dysfunction: impaired renal function in susceptible patients.

Before prescribing cefalexin, clinicians should consider several safety factors.

• Renal impairment: adjust dose in patients with reduced kidney function.
• Allergy history: avoid in individuals with known hypersensitivity to cephalosporins or penicillins.
• Pregnancy: use only if the potential benefit justifies the potential risk to the fetus.
• Breastfeeding: assess risk versus benefit before administration to nursing mothers.
• Concomitant medications: monitor for interactions that may affect drug levels.
• Store at ambient temperature: keep below 25°C in the original packaging, protected from moisture and direct sunlight.

Cefalexin can affect, or be affected by, several other medicines.

Major Interactions (Avoid)

• Probenecid: reduces renal excretion of cefalexin, increasing plasma concentrations.
• Live bacterial vaccines: oral vaccines may be less effective due to antibacterial activity.

Moderate Interactions (Monitor Closely)

• Warfarin: may enhance anticoagulant effect, requiring INR monitoring.
• Oral contraceptives: reduced efficacy possible; advise backup contraception.
• Metformin: may increase plasma levels, monitor for lactic acidosis.
• Aminoglycosides: additive nephrotoxicity risk; assess renal function.
• Loop diuretics: potential for increased ototoxicity when combined with other nephrotoxic agents.