CEPHALEXIN — 250 mg / 500 mg / 750mg capsules and tablets

Cephalexin is a first‑generation cephalosporin antibiotic that has been widely used since its approval in 1971. It is bactericidal and works by inhibiting bacterial cell wall synthesis, leading to cell lysis and death. As a first‑generation agent, it has excellent activity against Gram‑positive cocci, including streptococci and staphylococci (including penicillinase‑producing strains, though not methicillin‑resistant Staphylococcus aureus, MRSA), and moderate activity against some Gram‑negative organisms.

Mechanism of action: Cephalexin binds to penicillin‑binding proteins (PBPs) located inside the bacterial cell wall, inhibiting the final transpeptidation step of peptidoglycan synthesis. This interferes with cell wall integrity and activates autolytic enzymes, resulting in bacterial cell death. It is stable in the presence of gastric acid and well absorbed after oral administration, with peak plasma concentrations reached in approximately 1 hour.

Clinical indications: Cephalexin is indicated for the treatment of a wide range of infections caused by susceptible organisms. In respiratory tract infections, it is effective against Streptococcus pyogenes (group A beta‑hemolytic streptococci) for pharyngitis and tonsillitis, and against Streptococcus pneumoniae for community‑acquired pneumonia. In otitis media, it is active against S. pneumoniae, H. influenzae, S. aureus, and S. pyogenes. For skin and soft tissue infections, it is a first‑line choice for cellulitis, wound infections, abscesses, and impetigo caused by staphylococci and streptococci. It is also used for bone infections (osteomyelitis) due to susceptible staphylococci, and for urinary tract infections caused by E. coli, Klebsiella pneumoniae, and Proteus mirabilis.

Limitations of use: Cephalexin is not effective against MRSA, enterococci, or most anaerobic bacteria. It has limited activity against Pseudomonas, Acinetobacter, and many Enterobacteriaceae that have acquired resistance. It should be used only for proven or strongly suspected bacterial infections to reduce the development of drug‑resistant bacteria. Streptococcal infections (including prophylaxis of rheumatic fever) should be treated for at least 10 days.

• History of serious hypersensitivity reaction (e.g., anaphylaxis) to cephalexin, any cephalosporin antibiotic, or other beta‑lactam antibiotics.
• Known hypersensitivity to any component of the formulation.

• Probenecid: Decreases renal tubular secretion of cephalexin, increasing and prolonging cephalexin blood levels. Not recommended.
• Oral anticoagulants (warfarin): May increase INR and bleeding risk. Monitor coagulation parameters closely.
• Metformin: Cephalexin may increase metformin concentrations due to competition for renal tubular transport. Monitor for metformin toxicity.
• Oral contraceptives: Limited evidence suggests cephalosporins may rarely reduce efficacy of hormonal contraceptives. Advise patients to use additional non‑hormonal contraception (condoms) during treatment and for 7 days after stopping.
• Nephrotoxic drugs (aminoglycosides, loop diuretics): Caution with concomitant use; monitor renal function.
• Live vaccines (typhoid, cholera, BCG): Antibiotics may reduce vaccine effectiveness. Avoid concurrent administration.

• Pregnancy: FDA Category B. Animal studies do not indicate risk. Widely used in pregnancy when indicated.
• Breastfeeding: Cephalexin is excreted in breast milk in small amounts. Considered compatible with breastfeeding; monitor infant for diarrhea, rash, or thrush.
• Pediatric use: Safety established. Dosing based on weight and age. For children over 1 year: 25‑50 mg/kg/day in divided doses every 6‑12 hours. For severe infections, up to 100 mg/kg/day in divided doses.
• Geriatric use: No specific problems demonstrated, but elderly more likely to have age‑related renal impairment; dose adjustment may be needed.
• Renal impairment: GFR 30‑50 mL/min: 500 mg every 8‑12 hours. GFR 15‑29 mL/min: 250 mg every 8‑12 hours. GFR less than 15 mL/min: 250 mg every 12‑24 hours. Hemodialysis: 250‑500 mg after each dialysis session.
• Hepatic impairment: No dose adjustment needed (not significantly metabolized by liver).

• Symptoms: Nausea, vomiting, epigastric distress, diarrhea, hematuria (rare). Seizures reported with very high doses in patients with renal impairment.
• Management: Supportive care, monitoring of vital signs, fluid monitoring, correction of electrolyte imbalances. Activated charcoal may be considered if recent ingestion. Hemodialysis removes cephalexin.