Cephalexin Dosage for Adults with Bacterial Infections
The standard adult dosage of cephalexin for bacterial infections is 250 mg every 6 hours or 500 mg every 12 hours, with a total daily dosage ranging from 1 to 4 grams divided throughout the day. 1
Standard Dosing Regimens
- For most infections, the usual adult dose is 250 mg every 6 hours (1 gram total daily) 1
- For streptococcal pharyngitis, skin and skin structure infections, and uncomplicated cystitis in patients over 15 years of age, 500 mg every 12 hours is effective 1
- For skin and soft tissue infections, 500 mg three times per day is recommended by the Infectious Diseases Society of America 2
- For more severe infections or those caused by less susceptible organisms, larger doses may be needed, up to the maximum of 4 grams daily 1
Specific Infection Types and Dosing
Skin and Soft Tissue Infections
- For methicillin-susceptible S. aureus skin infections: 500 mg four times daily 3
- For impetigo: 250 mg four times daily 3
- For surgical site infections: 500 mg every 6 hours 3
Urinary Tract Infections
- For uncomplicated cystitis: 500 mg every 12 hours for 7-14 days 1
- Recent research suggests that twice-daily dosing (500 mg BID) is as effective as four-times-daily dosing for uncomplicated UTIs in women 4
- For chronic UTIs, 1 gram twice daily has shown comparable efficacy to four-times-daily dosing 5
Duration of Therapy
- For skin and soft tissue infections: typically 7 days 3
- For streptococcal pharyngitis: minimum 10 days to prevent rheumatic fever 1
- For urinary tract infections: 7-14 days 1
Important Clinical Considerations
- If daily doses greater than 4 grams are required, parenteral cephalosporins should be considered instead 1
- Cephalexin is not effective against methicillin-resistant Staphylococcus aureus (MRSA) 3
- Dosage adjustment is necessary in patients with renal impairment, particularly when creatinine clearance is less than 30 ml/min 6
- The dosage should be reduced proportionally to the reduced kidney function, which can be determined by creatinine clearance or serum creatinine 6
Pharmacokinetic Considerations
- Cephalexin is rapidly absorbed in the upper intestine (not the stomach) 6
- 70-100% of the dose is found in the urine 6-8 hours after administration 6
- Urine concentrations of 500-1000 μg/ml follow 250-500 mg oral doses, which far exceeds the minimum inhibitory concentration for common urinary tract pathogens 6