Cefalexin Drug Profile

What is Cefalexin?

Cefalexin is a first-generation cephalosporin antibiotic used to treat bacterial infections throughout the body. As a member of the beta-lactam antibiotic family, it works by disrupting bacterial cell wall formation, making it effective against many gram-positive bacteria and some gram-negative organisms. It is commonly prescribed for skin infections, respiratory tract infections, and urinary tract infections.

Uses

• Skin and soft tissue infections: Treats cellulitis, wound infections, and abscesses caused by susceptible bacteria like Staphylococcus and Streptococcus species
• Respiratory tract infections: Effective for treating pneumonia, bronchitis, and throat infections when caused by sensitive bacterial strains
• Urinary tract infections: Used to treat cystitis and other UTIs caused by E. coli and other susceptible gram-negative bacteria
• Bone and joint infections: Prescribed for osteomyelitis and septic arthritis when caused by appropriate bacterial pathogens
• Prophylaxis: Sometimes used to prevent infections before certain surgical procedures or in patients at high risk of bacterial endocarditis

How it works

Cefalexin works by inhibiting bacterial cell wall synthesis, specifically targeting enzymes called penicillin-binding proteins that are essential for building the peptidoglycan layer of bacterial cell walls. When bacteria cannot properly construct their cell walls, they become structurally weak and eventually die. This bactericidal action makes cefalexin effective against actively growing bacteria, particularly gram-positive organisms like staphylococci and streptococci.

Side effects

Common side effects:

• Nausea and vomiting
• Diarrhea
• Abdominal pain or cramping
• Headache
• Dizziness
• Skin rash or itching
• Vaginal yeast infections
• Fatigue

Serious side effects to watch for:

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• Severe allergic reactions including difficulty breathing, swelling of face or throat
• Clostridioides difficile-associated diarrhea (CDAD) with severe, persistent, or bloody diarrhea
• Stevens-Johnson syndrome or other severe skin reactions
• Severe kidney problems, especially in patients with pre-existing kidney disease
• Seizures, particularly in patients with kidney impairment or those taking high doses

Warnings and precautions

• Allergy history: Patients with known allergies to penicillins or other cephalosporins should use cefalexin with extreme caution, as cross-reactivity can occur in 5-10% of penicillin-allergic patients
• Kidney function: Dosage adjustments are necessary for patients with reduced kidney function, as cefalexin is primarily eliminated through the kidneys
• Pregnancy and breastfeeding: Generally considered safe during pregnancy (FDA Category B) and compatible with breastfeeding, though small amounts pass into breast milk
• Superinfections: Prolonged use may lead to overgrowth of resistant organisms or fungal infections, requiring monitoring for new symptoms
• Blood disorders: Rare cases of blood cell abnormalities have been reported, particularly with prolonged treatment

Interactions

• Probenecid: Increases cefalexin blood levels by reducing kidney elimination, potentially requiring dose adjustments
• Metformin: Cefalexin may increase metformin concentrations, raising the risk of lactic acidosis in diabetic patients
• Warfarin: May enhance anticoagulant effects, requiring more frequent INR monitoring and possible dose adjustments
• Live vaccines: Antibiotics may reduce the effectiveness of live bacterial vaccines like typhoid vaccine
• Aminoglycosides: Concurrent use may increase risk of kidney toxicity, especially in patients with pre-existing kidney problems
• Loop diuretics: May increase risk of kidney damage when used together, particularly furosemide
• Oral contraceptives: May reduce effectiveness of birth control pills, though this interaction is considered less likely with cefalexin than with some other antibiotics
• Cholestyramine: May reduce absorption of cefalexin if taken simultaneously

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Dosage

Adult dosing typically ranges from 250 mg to 1000 mg every 6 to 12 hours, depending on the severity and type of infection being treated. For most common infections, the standard dose is 500 mg every 12 hours or 250 mg every 6 hours. More severe infections may require 1000 mg every 6 to 8 hours. Treatment duration usually ranges from 7 to 14 days, though some conditions may require longer courses. Patients with kidney impairment require dose reductions based on creatinine clearance. Always follow your healthcare provider’s specific dosing instructions, as individual factors such as age, weight, kidney function, and infection severity will determine the most appropriate dose and duration for your situation.

Sources: FDA DailyMed drug labels (public domain), BNF, WHO Essential Medicines List. This article is for informational purposes only and does not constitute medical advice. Always consult your healthcare provider before starting or stopping any medication.

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