What is the recommended dosing for Keflex (Cephalexin) in an elderly diabetic woman with a foot infection and potential impaired renal function?

Keflex (Cephalexin) Dosing for Diabetic Foot Infection with Potential Renal Impairment

For an elderly diabetic woman with a foot infection and potential renal impairment, use cephalexin 500 mg every 12 hours for skin and soft tissue infection, with dose reduction required if creatinine clearance is below 30 mL/min. 1

Standard Dosing for Diabetic Foot Infections

• For skin and soft tissue infections, administer 500 mg every 12 hours orally 1
• The usual adult dose range is 1-4 grams daily in divided doses, with 250 mg every 6 hours being the standard regimen 1
• For more severe infections, larger doses may be needed, but if daily doses exceed 4 grams, parenteral cephalosporins should be considered 1

Critical Consideration: Renal Function Assessment

You must assess renal function before initiating therapy, as this patient has potential renal impairment. 2

• Measure serum creatinine and calculate creatinine clearance (CrCl) immediately 2
• Elderly diabetic patients are at high risk for chronic kidney disease, which significantly affects cephalexin dosing 2

Dose Adjustment for Renal Impairment

If CrCl is less than 30 mL/min, reduce the cephalexin dose proportionally to the reduced renal function 3

• Cephalexin is 70-100% renally excreted within 6-8 hours, making dose adjustment essential in renal impairment 3
• In patients with severe renal failure, the serum half-life increases from 1.1 hours (normal) to 6-18 hours, leading to drug accumulation 4
• For CrCl <30 mL/min, consider reducing frequency to every 24 hours or reducing individual doses by 50% 5, 3

Treatment Duration

Treat for 1-2 weeks for uncomplicated skin and soft tissue diabetic foot infections 2

• Antibiotics should be discontinued once clinical signs and symptoms of infection have resolved, even if the wound has not completely healed 2
• For more extensive infections or those with severe peripheral artery disease, consider extending treatment to 3-4 weeks 2
• If evidence of infection persists after 4 weeks of appropriate therapy, re-evaluate the patient and reconsider diagnostic studies 2

Important Caveats for This Patient Population

First-generation cephalosporins like cephalexin have significant limitations for diabetic foot infections:

• Cephalexin provides coverage primarily against methicillin-sensitive Staphylococcus aureus (MSSA) and streptococci, but has limited activity against many gram-negative organisms commonly found in diabetic foot infections 2
• Diabetic foot infections are typically polymicrobial, often requiring broader spectrum coverage 6
• If the infection is moderate to severe (limb-threatening), cephalexin is inadequate and parenteral broad-spectrum antibiotics are required 2, 6

Monitoring Requirements

• Monitor renal function (serum creatinine) during treatment, especially in elderly patients 2
• Assess clinical response within 48-72 hours; lack of improvement warrants culture-directed therapy adjustment 2
• In patients with renal impairment, antimicrobial activity may persist for 24 hours after dosing, requiring less frequent administration 4

When Cephalexin is Inappropriate

Do not use cephalexin for:

• Moderate or severe diabetic foot infections requiring hospitalization 2
• Infections with suspected Pseudomonas aeruginosa (especially in warm climates or if previously isolated) 2
• Suspected or confirmed osteomyelitis, which requires different antibiotic selection and prolonged therapy 2
• Patients with CrCl <10 mL/min on hemodialysis, where timing with dialysis becomes critical 5