How to use Cetil (Cephalexin) 500?

How to Use Cetil (Cephalexin) 500 mg

Cephalexin 500 mg should be taken orally either three times daily or four times daily for most infections, with the specific frequency depending on the type and severity of infection being treated. 1

Standard Dosing Regimens

For Adults and Adolescents

• Most common infections: 500 mg four times daily (every 6 hours) 1
• Alternative dosing: 500 mg three times daily for certain infections 1
• Streptococcal pharyngitis: 500 mg twice daily for 10 days 1

Duration of Treatment

• Typical course: 10 days for most infections including streptococcal pharyngitis 1
• Skin and soft tissue infections: 7-10 days depending on clinical response 2
• Chronic suppression therapy: May be continued indefinitely for prosthetic joint infections at 500 mg three or four times daily 1

Administration Guidelines

• Absorption: Cephalexin is absorbed in the upper intestine, not the stomach, so it can be taken with or without food 3
• High oral doses: Can be administered without significant gastrointestinal irritation 3
• Does not disturb lower bowel flora: Due to absorption high in the intestinal tract 3

Specific Clinical Indications

Respiratory Tract Infections

• Lower respiratory tract infections (acute/chronic bronchitis, pneumonia): 500 mg three to four times daily 1
• Upper respiratory tract infections (otitis media, sinusitis, tonsillitis, pharyngitis): Standard dosing applies 1

Skin and Soft Tissue Infections

• Methicillin-susceptible staphylococcal infections: 500 mg three to four times daily 1, 4
• Beta-hemolytic streptococcal infections: 500 mg three to four times daily 1

Urinary Tract Infections

• Uncomplicated UTI: May use lower dose of 125 mg twice daily in some cases 5
• Complicated UTI or pyelonephritis: 500 mg three to four times daily 5
• Achieves urinary concentrations: 500-1000 micrograms/ml, far exceeding minimum inhibitory concentrations for common uropathogens 3

Prosthetic Joint Infections

• Chronic oral suppression for oxacillin-susceptible staphylococci: 500 mg three or four times daily indefinitely 1
• Alternative to rifampin-based regimens: When rifampin cannot be used or as secondary companion drug 1

Important Dosing Adjustments

Renal Impairment

• Creatinine clearance <30 ml/min: Dose reduction required proportional to reduced renal function 4, 3
• Monitoring: Determine creatinine clearance or serum creatinine to guide dosing 3
• Excretion: 70-100% of dose appears in urine within 6-8 hours 3

Pediatric Considerations

• Children require higher doses per kilogram than adults due to greater body water turnover 3
• Streptococcal pharyngitis in children: 20 mg/kg/dose twice daily (maximum 500 mg/dose) for 10 days 1

Critical Contraindications and Caveats

Allergy Considerations

• Avoid in immediate-type penicillin hypersensitivity: Due to cross-reactivity risk 1, 4
• Low incidence of allergy overall: Due to chemical stability and configuration 3

Antimicrobial Spectrum Limitations

• NOT effective against MRSA: Alternative agents required for methicillin-resistant staphylococci 4, 2
• NOT effective against oxacillin-resistant coagulase-negative staphylococci: Use alternative agents 1
• Does not penetrate CNS: Not appropriate for meningitis 3

Monitoring and Safety

Clinical Monitoring

• Monitor for efficacy and toxicity: Based on clinical judgment during treatment 1
• Watch for Clostridium difficile colitis: Possible with any antimicrobial 1
• Adverse effects: Generally mild and transient, primarily gastrointestinal disturbances 3

Drug Selection Based on Susceptibility

• Choose based on in vitro susceptibility testing: When available 1
• Consider patient allergies and intolerances: Before prescribing 1
• Check for potential drug interactions: Especially in patients on multiple medications 1

Practical Alternatives

If compliance is a concern with three to four times daily dosing, cefadroxil 500 mg twice daily or 1000 mg twice daily is therapeutically equivalent and may improve adherence 4. However, cephalexin remains the preferred first-generation cephalosporin due to its narrow spectrum, low cost, and extensive clinical experience 1.