What is the usual adult dose for cephalexin?

Usual Adult Dose for Cephalexin

The standard adult dose of cephalexin is 250 mg every 6 hours (four times daily), with 500 mg every 6 hours commonly used for more significant infections such as skin and soft tissue infections caused by methicillin-susceptible Staphylococcus aureus. 1

Standard Dosing Regimens

General Infections

• The FDA-approved adult dosage ranges from 1 to 4 grams daily in divided doses 1
• 250 mg every 6 hours (four times daily) is the usual adult dose for most infections 1
• For more severe infections or those caused by less susceptible organisms, larger doses may be needed 1

Specific Infection Types

Skin and Soft Tissue Infections:

• 500 mg four times daily (every 6 hours) is recommended by the Infectious Diseases Society of America for MSSA infections 2
• This dosing provides adequate tissue concentrations to treat staphylococcal infections 2

Streptococcal Pharyngitis, Uncomplicated Cystitis, and Skin Infections:

• 500 mg every 12 hours (twice daily) may be administered for these specific conditions in patients over 15 years of age 1
• Cystitis therapy should be continued for 7 to 14 days 1
• Recent evidence supports that twice-daily dosing (500 mg BID) is as effective as four-times-daily dosing for uncomplicated urinary tract infections 3

Respiratory Tract Infections:

• 500 mg four times daily for adults 2

Dosing Schedule Considerations

• The standard dosing interval is every 6 hours to maintain consistent antibiotic levels 2
• For streptococcal infections, cephalexin must be administered for at least 10 days to prevent rheumatic fever 2, 1
• More severe infections requiring higher sustained drug levels necessitate four times daily dosing 2

Maximum Dosing and Escalation

• If daily doses exceeding 4 grams are required, parenteral cephalosporins (such as cefazolin 1 g IV every 8 hours) should be considered 2, 1

Important Clinical Caveats

Renal Impairment:

• Patients with creatinine clearances less than 30 mL/min require dosage reduction proportional to reduced renal function 4
• Cephalexin is rapidly cleared by the kidneys, with 70-100% of the dose found in urine 6-8 hours after each dose 4

Spectrum Limitations:

• Cephalexin has poor activity against Haemophilus influenzae, Moraxella catarrhalis, and is completely ineffective against MRSA 2
• It should not be used for acute bacterial sinusitis due to poor H. influenzae coverage 2
• Cephalexin has limited coverage against anaerobes, making it unsuitable for deep abscesses or anaerobic infections 2