What is the recommended dose of cephalexin for an adult patient with normal renal function and a suspected bacterial infection?

Cephalexin Dosing for Adults with Normal Renal Function

For adults with normal renal function and suspected bacterial infection, cephalexin should be dosed at 250 mg every 6 hours for mild infections, or 500 mg every 12 hours for streptococcal pharyngitis, skin and skin structure infections, and uncomplicated cystitis. 1

Standard Adult Dosing Regimens

The FDA-approved dosing range for cephalexin in adults is 1 to 4 grams daily in divided doses 1:

• Mild infections: 250 mg every 6 hours (1 gram total daily) 1
• Moderate infections (streptococcal pharyngitis, skin/soft tissue infections, uncomplicated cystitis): 500 mg every 12 hours 1
• Severe infections or less susceptible organisms: Higher doses may be required, up to 4 grams daily 1

Infection-Specific Dosing

Uncomplicated Cystitis

• Dose: 500 mg every 12 hours 1
• Duration: 7 to 14 days 1
• Patient population: Adults over 15 years of age 1

Streptococcal Pharyngitis

• Dose: 500 mg every 12 hours 1
• Duration: At least 10 days for β-hemolytic streptococcal infections 1

Skin and Skin Structure Infections

• Dose: 500 mg every 12 hours 1
• Duration: Based on clinical response, typically 7-10 days 1

Critical Dosing Considerations

Maximum daily dose: If doses greater than 4 grams daily are required, parenteral cephalosporins should be considered instead 1

Pharmacokinetic advantages: Cephalexin is totally and rapidly absorbed in the upper intestine, achieving urinary concentrations of 500-1000 mcg/mL following 250-500 mg oral doses—many times greater than the minimum inhibitory concentration for common urinary pathogens 2

Renal clearance: 70-100% of the dose is excreted unchanged in urine within 6-8 hours, making it highly effective for urinary tract infections 2

Common Pitfalls to Avoid

• Do not reduce dosing in normal renal function: Dose reduction is only necessary when creatinine clearance falls below 30 mL/min 2
• Do not underdose severe infections: For more severe infections or those caused by less susceptible organisms, larger doses within the 1-4 gram daily range are needed 1
• Ensure adequate treatment duration: For β-hemolytic streptococcal infections, a minimum 10-day course is mandatory to prevent rheumatic fever 1

Storage and Administration

After reconstitution of suspension formulations, refrigerate and use within 14 days 1. The drug can be administered without regard to meals, as it is absorbed high in the intestinal tract and does not disturb lower bowel flora 2.