Cephalexin (Keflex) Dosing and Duration for Acute Bacterial Tonsillitis
For Group A streptococcal pharyngitis/tonsillitis, cephalexin should be dosed at 20 mg/kg/dose twice daily (maximum 500 mg per dose) for 10 days in children, and 500 mg four times daily for 10 days in adults. 1, 2
Standard Dosing Regimens
Adults
- 500 mg four times daily (every 6 hours) for 10 days 2
- Alternative: 250 mg four times daily for milder infections 2
- The FDA label specifies that for streptococcal pharyngitis, 500 mg every 12 hours may be administered 2
Children
- 20 mg/kg/dose twice daily (maximum 500 mg per dose) for 10 days 1, 3, 4
- For severe infections, dosage may be doubled 2
- The total daily dose ranges from 25-50 mg/kg/day in divided doses 5, 6
Duration of Treatment
The treatment duration must be 10 days for Group A streptococcal infections to prevent acute rheumatic fever and other complications. 1, 7, 4, 2 This is non-negotiable—shorter courses are inadequate for streptococcal pharyngitis, even though patients typically feel better after a few days.
Renal Dosing Adjustments
In patients with impaired renal function (creatinine clearance <30 mL/min), cephalexin dosing requires adjustment. 2, 8, 9
- Dosage reduction should be proportional to the degree of renal impairment 8
- Studies suggest the dosing interval may need to be prolonged up to 20 times normal in severe renal failure, far more than creatinine clearance alone would suggest 9
- Monitor patients with markedly impaired renal function carefully, as safe dosage may be lower than usually recommended 2
- For patients on hemodialysis, cephalexin is removed during dialysis (58% reduction over 6 hours), so timing of doses relative to dialysis should be considered 10
Important Clinical Considerations
Efficacy Context
Cephalexin is recommended as a first-line alternative for penicillin-allergic patients (except those with immediate hypersensitivity reactions) 1, 3, 4. Research demonstrates cephalexin may actually be more effective than penicillin for Group A streptococcal throat infections, with combined treatment failure rates of 10% versus 19% for penicillin 11.
Common Pitfalls to Avoid
- Do not use cephalexin for suspected MRSA infections—it is inactive against MRSA 5, 6
- Do not use first-generation cephalosporins like cephalexin for Lyme disease—they are inactive against Borrelia burgdorferi 12
- Avoid in patients with immediate-type penicillin hypersensitivity due to cross-reactivity risk 1, 3, 4
- Do not shorten the 10-day course even if symptoms resolve earlier—this increases treatment failure and bacterial resistance 2