What is the recommended dosage of Keflex (Cephalexin) for urinary tract infections in patients with impaired renal function on dialysis?

Keflex Dosing for UTI in Dialysis Patients

For patients on hemodialysis with UTI, administer Cephalexin (Keflex) 250-500 mg after each dialysis session, as the drug is significantly removed during dialysis and achieves adequate urinary concentrations even in anephric patients. 1

Dosing Rationale and Pharmacokinetics

Cephalexin remains effective for UTI treatment in dialysis patients because:

• Even in anephric patients, urinary concentrations of cephalexin remain adequate for treating most common UTI pathogens including E. coli, Klebsiella, and Proteus mirabilis 1
• Single doses of 250-500 mg produce high, prolonged serum concentrations in patients without kidney function, with peak levels typically occurring within 1 hour (though delayed absorption up to 6-12 hours can occur in some patients) 1
• Hemodialysis removes approximately 58% of serum cephalexin over a 6-hour session, necessitating post-dialysis administration 1

Specific Dosing Algorithm

For patients on hemodialysis:

• Administer 250-500 mg orally after each dialysis session 1
• Always give the medication after dialysis, never before, to prevent premature drug removal and maintain therapeutic levels 2
• On non-dialysis days, extend the dosing interval rather than reducing the dose, as is standard practice for patients with creatinine clearance <30 mL/min 2

Treatment Duration

• For complicated UTIs, treat for 7-14 days, adjusting based on clinical response 2
• The drug maintains full antimicrobial activity in urine against common uropathogens 3

Critical Pitfalls to Avoid

• Do not administer before dialysis - this leads to subtherapeutic levels due to drug removal during the session 2
• Do not use standard dosing regimens designed for patients with normal renal function, as this causes drug accumulation and potential toxicity 2
• Avoid nephrotoxic drug combinations to protect any residual renal function, which is particularly important as some patients may regain kidney function 4
• Be aware that 2 out of 6 anephric patients in one study showed delayed absorption (6-12 hours), so if clinical response is suboptimal, consider this pharmacokinetic variability 1

Monitoring Considerations

• Cephalexin is essentially nontoxic at recommended doses 3
• The drug achieves urinary concentrations routinely exceeding 1000 mg/L even after small doses 5
• Consider consulting nephrology to coordinate timing with dialysis schedule and ensure optimal therapeutic outcomes 6