What is the recommended dose of Keflex (Cephalexin) for an adult with an ear infection?

Keflex (Cephalexin) Dosing for Adult Ear Infections

For adult ear infections, Keflex (cephalexin) should be dosed at 500 mg orally every 12 hours, as this is the FDA-approved regimen for upper respiratory tract infections including otitis media. 1

Standard Dosing Regimen

• The FDA label specifies 500 mg every 12 hours for streptococcal pharyngitis, skin and skin structure infections, and uncomplicated cystitis in patients over 15 years of age 1
• The general adult dosage range is 1 to 4 grams daily in divided doses, with the usual dose being 250 mg every 6 hours 1
• For more severe infections or less susceptible organisms, larger doses may be needed 1

Duration of Treatment

• Treatment should continue for 7-10 days for most upper respiratory tract infections 1, 2
• Clinical studies have demonstrated that cephalexin at dosages of 1-2 g/day in adults is effective for upper respiratory tract infections 2

Clinical Efficacy Considerations

• Cephalexin is effective against the most common pathogens causing ear infections, including Streptococcus pneumoniae and beta-hemolytic streptococci 2, 3
• However, cephalexin has poor activity against Haemophilus influenzae, with failure rates of approximately 50% when this organism is the causative pathogen 2
• If H. influenzae is suspected or confirmed (particularly in adults with chronic otitis media or those who fail initial therapy), alternative antibiotics with better H. influenzae coverage should be considered, such as amoxicillin-clavulanate 4, 5

Important Clinical Pitfalls

• Do not use cephalexin as monotherapy if H. influenzae is likely, as this is a common cause of treatment failure in otitis media 2
• The drug is well-absorbed in the upper intestine and achieves rapid tissue distribution, but does not penetrate into host cells 3
• Patients with creatinine clearance less than 30 mL/min require dose reduction proportional to their reduced renal function 3
• Adverse effects are relatively infrequent (mostly gastrointestinal upset, rash, urticaria) and rarely require discontinuation 2

When to Consider Alternative Therapy

• If the patient fails to improve after 48-72 hours, consider switching to an agent with better H. influenzae coverage such as amoxicillin-clavulanate 875/125 mg twice daily 5
• For patients with penicillin/cephalosporin allergies, alternative agents should be selected 1
• Cephalexin is NOT effective against MRSA; if MRSA is suspected, alternative coverage is required 6