What is the classification of Keflex (cephalexin)?

Classification of Keflex (Cephalexin)

Keflex (cephalexin) is classified as a first-generation cephalosporin antibiotic in the beta-lactam family. 1, 2

Chemical Structure and Classification Details

• Cephalexin is a semisynthetic cephalosporin antibiotic with the chemical structure 7-(D-α-amino-α-phenylacetamido)-3-methyl-3-cephem-4-carboxylic acid, monohydrate 1
• It belongs to the beta-lactam class of antibiotics, which differs from penicillins in the structure of the bicyclic ring system 1
• As a first-generation cephalosporin, it has a D-phenylglycyl group as substituent at the 7-amino position and an unsubstituted methyl group at the 3-position 1

Antimicrobial Spectrum and Activity

• First-generation cephalosporins like cephalexin have a narrow gram-negative spectrum but are most active against gram-positive bacteria, particularly Staphylococcus aureus 2
• Cephalexin is effective against many common pathogens including streptococci and staphylococci, making it useful for skin, soft tissue, respiratory, and urinary tract infections 3
• It is commonly used in the empirical treatment of mild skin and soft tissue infections, particularly those caused by gram-positive cocci 4
• Cephalexin has shown cure rates of 90% or higher in the treatment of streptococcal and staphylococcal skin infections 5

Pharmacokinetic Properties

• Cephalexin is not absorbed from the stomach but is totally and rapidly absorbed in the upper intestine 3
• It demonstrates dose-proportional increases in maximum plasma concentration (Cmax) and area under the curve (AUC) 6
• The drug is rapidly cleared from the body by the kidneys, with 70-100% of the dose found in the urine 6-8 hours after administration 3
• Dosage adjustment is required in patients with creatinine clearance less than 30 ml/min 3

Cross-Reactivity Considerations

• Cephalexin shares R1 side chains with amoxicillin and ampicillin, which may lead to cross-reactivity in patients with confirmed penicillin allergies 4
• In patients with proven penicillin allergy, the risk of cross-reactivity to aminocephalosporins like cephalexin is approximately 16.45% (95% CI: 11.07-23.75) 4
• For patients with a history of anaphylaxis, angioedema, or urticaria with penicillins or ampicillin, cephalexin should not be used due to possible cross-reactions 4

Clinical Applications

• Cephalexin is used in the treatment of:
  • Skin and soft tissue infections 4, 5
  • Upper respiratory tract infections 7
  • Urinary tract infections 3
  • Mild diabetic foot infections without complicating factors 4
• It can be administered as prophylaxis for certain dental procedures in patients at risk of infective endocarditis 4
• Cephalexin is available in oral formulations (capsules, tablets, and suspension) 1

Dosing Considerations

• Typical adult dosing is 500 mg orally every 6 hours 4
• Pediatric dosing ranges from 20-100 mg/kg/day 7
• For antimicrobial prophylaxis, a 2g oral dose is recommended for adults and 50 mg/kg for children 4

Understanding cephalexin's classification as a first-generation cephalosporin is important for clinical decision-making, particularly when considering cross-reactivity in patients with beta-lactam allergies and when selecting appropriate antibiotics based on the suspected pathogens and infection site.