What is the typical dose of Keflex (Cephalexin) for urinary tract infections or skin infections?

Keflex (Cephalexin) Dosing

For uncomplicated urinary tract infections in adults, cephalexin 500 mg twice daily for 7-14 days is as effective as the traditional four-times-daily dosing and should be preferred for improved adherence. 1, 2

Urinary Tract Infections

Uncomplicated Cystitis (Adults >15 years)

• Standard dosing: 500 mg every 12 hours (twice daily) for 7-14 days 1
• The FDA label specifies this regimen for uncomplicated cystitis in patients over 15 years of age 1
• A 2023 study demonstrated that twice-daily dosing (500 mg BID) achieved equivalent treatment failure rates (12.7%) compared to four-times-daily dosing (17%), with no statistical difference (P = 0.343) 2
• The twice-daily regimen offers better adherence without compromising efficacy 2

Alternative Dosing for UTI

• Traditional regimen: 250 mg every 6 hours (four times daily) 1
• For more severe infections or less susceptible organisms, larger doses may be needed 1
• Cephalexin achieves urinary concentrations of 500-1000 mcg/mL following 250-500 mg oral doses, far exceeding the minimum inhibitory concentration for typical urinary pathogens 3

Renal Impairment Considerations

• Patients with creatinine clearance <30 mL/min require dose reduction proportional to reduced renal function 3
• 70-100% of cephalexin is excreted unchanged in urine within 6-8 hours 3

Skin and Soft Tissue Infections

Uncomplicated Skin Infections (Adults)

• Standard dosing: 500 mg every 12 hours (twice daily) 1
• This applies to streptococcal pharyngitis and skin/skin structure infections 1

Methicillin-Susceptible Staphylococcus aureus (MSSA)

• Dosing: 500 mg four times daily (QID) orally 4
• Cephalexin is recommended for penicillin-allergic patients except those with immediate hypersensitivity reactions 4
• The availability of suspension formulation and less frequent dosing requirements make it practical for outpatient use 4

Severe or Complicated Skin Infections

• For infections requiring >4 g daily, parenteral cephalosporins should be considered instead 1
• The usual adult dosage range is 1-4 g daily in divided doses 1

Pediatric Dosing

General Pediatric Dosing

• Standard range: 25-50 mg/kg/day in divided doses 1
• For streptococcal pharyngitis and skin infections in children >1 year, the total daily dose may be divided every 12 hours 1

Specific Pediatric Indications

• Otitis media: 75-100 mg/kg/day in 4 divided doses 1
• Severe infections: Double the standard dosage 1
• β-hemolytic streptococcal infections: Administer therapeutic dosage for at least 10 days 1

Pediatric UTI

• A 3-day course of cephalexin 25-50 mg/kg/day achieved 90% immediate cure rates for acute lower urinary tract infections in children 5
• However, the FDA-approved duration for cystitis is 7-14 days 1

Important Clinical Considerations

Absorption and Administration

• Cephalexin is not absorbed from the stomach but is totally and rapidly absorbed in the upper intestine 3
• Can be administered in relatively high oral doses without gastrointestinal irritation 3
• Does not disturb lower bowel flora due to absorption high in the intestinal tract 3

Common Pitfalls to Avoid

• Do not use cephalexin for MRSA infections—it is only effective against methicillin-susceptible strains 4
• Do not exceed 4 g daily without switching to parenteral cephalosporins 1
• Do not forget dose adjustment in patients with creatinine clearance <30 mL/min 3
• Children may require higher doses per kilogram than adults due to greater body water turnover 3

Adverse Effects

• Generally mild and transient, including gastrointestinal disturbances, diarrhea, nausea, and vomiting 6
• Low incidence of allergy due to chemical stability and configuration 3
• Reported adverse events occurred in only 4.6-5.6% of patients in recent UTI studies 2