Cefalexin is a first-generation cephalosporin antibiotic with bactericidal activity against a wide range of Gram-positive and some Gram-negative bacteria. It is a beta-lactam antibiotic that inhibits bacterial cell wall synthesis. In India, it is widely prescribed for common community-acquired infections due to its good oral absorption, established safety profile, and cost-effectiveness.
Adult: 250-500 mg every 6 hours, OR 500 mg every 12 hours for less severe infections. Typical dose: 1-4 g per day in divided doses. For streptococcal pharyngitis: 500 mg twice daily for 10 days.
Note: Can be administered with or without food. Taking with food may minimize gastrointestinal upset. Capsules/Tablets should be swallowed whole with a full glass of water. The oral suspension must be shaken well before each use. Complete the entire prescribed course even if symptoms improve.
Cefalexin exerts its bactericidal effect by inhibiting the synthesis of the bacterial cell wall. It binds to specific penicillin-binding proteins (PBPs) located inside the bacterial cell wall. This binding inhibits the final transpeptidation step of peptidoglycan synthesis in the bacterial cell wall, leading to the formation of a defective cell wall and ultimately to osmotic lysis and cell death.
Pregnancy: Pregnancy Category B (US FDA). Animal studies have not shown teratogenicity. Use during pregnancy only if clearly needed. Epidemiological studies in humans show no clear evidence of adverse fetal outcomes. Considered a relatively safe option for treating infections in pregnancy when indicated.
Driving: Cefalexin may cause dizziness in some patients. Patients should be cautioned about operating machinery or driving until they are sure the medication does not affect them adversely.
| Probenecid | Decreases renal tubular secretion of cefalexin, leading to increased and prolonged blood levels. | Moderate |
| Metformin | Cefalexin may increase the blood concentration and effects of metformin by competing for renal tubular secretion. Monitor blood glucose. | Moderate |
| Oral Anticoagulants (Warfarin) | May potentiate anticoagulant effect; monitor INR closely. Mechanism may involve reduction of vitamin K-producing gut flora. | Moderate |
| Aminoglycosides (e.g., Gentamicin) | Potential additive nephrotoxicity, though risk with oral cefalexin is low. Monitor renal function. | Low |
| Live Bacterial Vaccines (e.g., Typhoid, BCG) | Antibiotics may diminish the therapeutic effect of live bacterial vaccines. Avoid concurrent use. | Moderate |