Overview
Cephalexin is a first-generation cephalosporin antibiotic that inhibits bacterial cell wall synthesis, leading to bacterial cell death. It is commonly prescribed for various bacterial infections including respiratory tract, skin, soft tissue, urinary tract, and bone infections. The drug is typically administered orally and is generally well-tolerated with a favorable safety profile.
Mechanism of Action
Cephalexin is a bactericidal antibiotic that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs). This interference prevents the final transpeptidation step of peptidoglycan synthesis in bacterial cell walls, leading to osmotic instability and cell lysis.
Indications
- Respiratory tract infections caused by susceptible Streptococcus pneumoniae and group A beta-hemolytic streptococci
- Skin and skin structure infections caused by susceptible staphylococci and/or streptococci
- Bone infections caused by susceptible staphylococci and/or Proteus mirabilis
- Genitourinary tract infections, including acute prostatitis caused by susceptible Escherichia coli, P. mirabilis, and Klebsiella species
- Otitis media caused by susceptible S. pneumoniae, Haemophilus influenzae, staphylococci, streptococci, and Neisseria catarrhalis
Common Doses
- 250 mg
- 500 mg
- 125 mg/5 mL oral suspension
- 250 mg/5 mL oral suspension
Dosage
Typical adult dosage is 250-500 mg every 6 hours, depending on infection severity and location. For more severe infections or those caused by less susceptible organisms, doses up to 4 grams daily may be required. Duration of therapy typically ranges from 7-14 days.
Contraindications
- Known hypersensitivity to cephalexin or other cephalosporins
- Patients with a history of severe hypersensitivity reactions (e.g., anaphylaxis) to any beta-lactam antibiotics
Side Effects
- Gastrointestinal: diarrhea, nausea, vomiting, abdominal pain, dyspepsia
- Hypersensitivity reactions: rash, urticaria, angioedema, anaphylaxis
- Central nervous system: dizziness, fatigue, headache
- Hematologic: eosinophilia, neutropenia, thrombocytopenia
- Hepatic: transient elevations in liver enzymes
- Renal: interstitial nephritis (rare)
Interactions
- Probenecid may decrease renal tubular secretion of cephalexin, increasing and prolonging serum concentrations
- Metformin: cephalexin may increase metformin concentrations, increasing risk of lactic acidosis
- Oral contraceptives: antibiotics may reduce contraceptive effectiveness; recommend additional contraceptive methods
Counseling Points
- Complete the full course of therapy even if symptoms improve
- Take with food if gastrointestinal upset occurs
- Report severe diarrhea, abdominal pain, or blood/mucus in stool immediately
- Inform healthcare provider of any rash, itching, or swelling
- Use additional contraceptive methods if taking oral contraceptives
- Space doses evenly throughout the day
- Shake oral suspension well before each use