What is the recommended dosage of Cefalexin (Cephalexin) for treating bacterial infections in adults?

Cefalexin (Cephalexin) Dosage for Bacterial Infections in Adults

For most adult bacterial infections, administer cephalexin 250-500 mg orally every 6 hours (four times daily), with the total daily dose ranging from 1-4 grams depending on infection severity. 1

Standard Adult Dosing by Indication

Skin and Soft Tissue Infections (SSTI)

• Mild to moderate SSTI: 500 mg orally four times daily 2
• Alternative regimen: 500 mg every 12 hours for streptococcal pharyngitis, skin infections, and uncomplicated cystitis 1
• Cephalexin is appropriate for methicillin-susceptible Staphylococcus aureus (MSSA) infections in penicillin-allergic patients (except those with immediate hypersensitivity reactions) 2

Impetigo

• Standard dose: 250 mg orally four times daily 2
• This lower dose is sufficient for superficial skin infections caused by Staphylococcus and Streptococcus species 2

Uncomplicated Urinary Tract Infections

• Standard regimen: 500 mg every 12 hours for 7-14 days 1
• Alternative regimen: 500 mg twice daily is as effective as four-times-daily dosing for uncomplicated UTI, with potential for improved adherence 3
• Cephalexin achieves urinary concentrations of 500-1000 mcg/mL following 250-500 mg oral doses, far exceeding minimum inhibitory concentrations for common uropathogens 4

Urologic Prophylaxis

• Periprocedural prophylaxis: 500 mg orally every 6 hours when oral prophylaxis is indicated 2
• This is used for patients undergoing genitourinary procedures with risk of bacteremia 2

Dosing Algorithm Based on Infection Severity

Mild Infections

• Start with 250 mg four times daily 1
• Appropriate for uncomplicated impetigo, minor skin infections, and prophylaxis 2

Moderate Infections

• Use 500 mg four times daily 2, 1
• This is the standard dose for most SSTI and documented MSSA infections 2

Severe Infections

• Double the standard dose as needed, but if daily doses exceed 4 grams are required, switch to parenteral cephalosporins 1
• For severe infections or less susceptible organisms, larger doses may be necessary 1

Critical Dosing Considerations

Renal Impairment

• Patients with creatinine clearance <30 mL/min require dose reduction proportional to reduced renal function 4
• Cephalexin is 70-100% renally eliminated within 6-8 hours of each dose 4

Absorption and Administration

• Cephalexin is completely absorbed in the upper intestine but not from the stomach 4
• Food delays absorption but does not significantly reduce bioavailability 4
• The suspension formulation provides convenience with less frequent dosing requirements, particularly useful when four-times-daily dosing is challenging 2

Duration of Therapy

• Streptococcal infections: Minimum 10 days of therapeutic dosing required 1
• Uncomplicated cystitis: 7-14 days 1
• Skin and soft tissue infections: Typically 7-10 days, though specific duration depends on clinical response 2

Common Pitfalls to Avoid

Do not use cephalexin for MRSA infections - it is inactive against methicillin-resistant Staphylococcus aureus and should only be used for documented MSSA or susceptible streptococcal infections 2

Avoid inadequate dosing frequency - while twice-daily dosing is effective for uncomplicated UTI 3, most other infections require four-times-daily administration to maintain adequate tissue concentrations 2, 1

Do not exceed 4 grams daily without switching to parenteral therapy - if higher doses are needed, parenteral cephalosporins are more appropriate 1

Ensure adequate treatment duration for streptococcal infections - premature discontinuation before 10 days increases risk of rheumatic fever and post-streptococcal glomerulonephritis 1

Practical Considerations

The availability of suspension formulations and the option for twice-daily dosing in select infections (uncomplicated cystitis, streptococcal pharyngitis, minor skin infections) makes cephalexin particularly suitable for outpatient therapy where adherence may be challenging 2, 1, 3. However, for most bacterial infections requiring cephalexin, the standard four-times-daily regimen remains the evidence-based recommendation 2, 1.