What is the appropriate twice-daily dose of cephalexin for a 5-year-old, 68.9-pound, 49-inch tall patient with strep throat who has failed penicillin therapy?

Cephalexin Dosing for Strep Throat in a 5-Year-Old After Penicillin Failure

For this 5-year-old patient (68.9 lbs/31.3 kg) with strep throat who failed penicillin therapy, prescribe cephalexin 500 mg twice daily for 10 days. 1

Weight-Based Calculation and Rationale

• The patient weighs 31.3 kg (68.9 lbs), placing them in the FDA dosing table category between 20 kg and 40 kg 1
• For streptococcal pharyngitis in pediatric patients, the FDA label specifically states that "the total daily dose may be divided and administered every 12 hours" 1
• Using the 250 mg/5 mL suspension formulation, the FDA recommends 1 to 2 teaspoons (250-500 mg) twice daily for patients in this weight range 1
• The standard pediatric dosage is 25-50 mg/kg/day in divided doses, which calculates to 782-1,565 mg/day for this 31.3 kg patient 1
• Prescribing 500 mg (2 teaspoons of 250 mg/5 mL suspension) twice daily provides 1,000 mg/day (32 mg/kg/day), which falls appropriately within the recommended range 1

Treatment Duration

• Administer cephalexin for at least 10 days to ensure adequate eradication of group A beta-hemolytic streptococcus 1, 2
• The FDA label explicitly states: "In the treatment of β-hemolytic streptococcal infections, a therapeutic dosage of cephalexin should be administered for at least 10 days" 1

Why Cephalexin After Penicillin Failure

• Penicillin failure rates in streptococcal pharyngitis have increased from 2-10% historically to approximately 30% in recent decades 3
• Cephalosporins, particularly cephalexin, have been demonstrated to be superior to penicillin at eradicating group A beta-hemolytic Streptococcus 3, 4
• First-generation cephalosporins are recommended options for patients with penicillin treatment failure 4
• Cephalexin achieves cure rates of 90% or higher in streptococcal infections and has proven efficacy with twice-daily dosing 5, 2

Practical Prescribing Details

• Use cephalexin 250 mg/5 mL oral suspension 1
• Dose: 10 mL (2 teaspoons) by mouth twice daily for 10 days 1
• The twice-daily regimen has been proven equally effective to four-times-daily dosing in multiple studies, with the advantage of enhanced medication compliance 2
• After mixing, store the suspension in the refrigerator and discard after 14 days 1

Common Pitfalls to Avoid

• Do not prescribe for less than 10 days, as shorter courses may lead to treatment failure and potential rheumatic fever complications 1
• Adverse effects are generally mild and infrequent, primarily consisting of gastrointestinal upset, rash, and urticaria 6
• Ensure the patient is not allergic to cephalosporins; approximately 10% of penicillin-allergic patients may have cross-reactivity with cephalosporins 4