Cephalexin

# Cephalexin ## Overview - **Classification**: First-generation cephalosporin antibiotic. - **Mechanism**: Inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), leading to cell lysis. ## Primary Indications 1. **Skin & Soft Tissue Infections**: Cellulitis, erysipelas, impetigo, folliculitis, furunculosis. 2. **Upper Respiratory Tract Infections**: Pharyngitis, tonsillitis, otitis media. 3. **Urinary Tract Infections**: Uncomplicated cystitis. 4. **Bone & Joint Infections**: Often as step-down therapy from IV antibiotics. ## Adult Dosing ### Standard Dosing **Skin and Soft Tissue Infections, Uncomplicated UTIs** - **Dose**: **250-500 mg** - **Frequency**: Every 6-12 hours (QID or BID) - **Route**: Oral - **Duration**: 7-14 days (varies by infection) **Pharyngitis/Tonsillitis** - **Dose**: **250 mg** - **Frequency**: Every 6 hours (QID) - **Route**: Oral - **Duration**: 10 days **Bone and Joint Infections** - **Dose**: **250-500 mg** - **Frequency**: Every 6 hours (QID) - **Route**: Oral - **Duration**: 4-6 weeks (longer for osteomyelitis) ### Dose Adjustments - **Renal Impairment**: Adjust based on CrCl. - CrCl 30-59 mL/min: **250-500 mg** q8-12h - CrCl 10-29 mL/min: **250 mg** q8-12h - CrCl <10 mL/min: **250 mg** q12-24h - **Hepatic Impairment**: No dose adjustment typically needed. - **Elderly Patients**: Adjust dose based on renal function; monitor for adverse effects. ## Pediatric Dosing ### Neonates (0-28 days) - **Dose**: Not routinely recommended; consult infectious disease specialist. - **Special Notes**: Limited data, potential for altered pharmacokinetics. ### Infants (1-12 months) - **Standard Dose**: **25-50 mg/kg/day** - **Frequency**: Divided every 8-12 hours (TID or BID) - **Maximum**: Up to **100 mg/kg/day** for severe infections (max **4 g/day**) - **Otitis Media**: **75-100 mg/kg/day** divided every 6-12 hours (QID or BID). ### Children (1-12 years) - **Standard Dose**: **25-50 mg/kg/day** - **Frequency**: Divided every 8-12 hours (TID or BID) - **Maximum**: Up to **100 mg/kg/day** for severe infections (max **4 g/day**) - **Otitis Media**: **75-100 mg/kg/day** divided every 6-12 hours (QID or BID). - **Formulations**: Oral suspension available (125 mg/5mL, 250 mg/5mL). ### Adolescents (13-18 years) - **Dose**: Adult dosing applies. - **Maximum**: Up to **4 g/day**. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to cephalexin or other cephalosporin antibiotics. - **Relative**: History of severe immediate hypersensitivity (e.g., anaphylaxis) to penicillin. ### Common Adverse Effects - **Common (1-10%)**: Diarrhea, nausea, vomiting, abdominal pain, dyspepsia, rash, candidiasis. - **Serious but Rare**: Anaphylaxis, Stevens-Johnson Syndrome (SJS), Toxic Epidermal Necrolysis (TEN), Clostridioides difficile infection (CDI), neutropenia, thrombocytopenia. ### Key Drug Interactions - **Metformin**: Cephalexin can increase metformin plasma concentrations. Monitor blood glucose. - **Probenecid**: May increase cephalexin levels by decreasing renal elimination. Not usually clinically significant. - **Warfarin**: Rare reports of increased INR/bleeding risk. Monitor INR closely if co-administered. ## Monitoring & Follow-up - **Before Treatment**: Assess drug allergies (especially to penicillin/cephalosporins). - **During Treatment**: Monitor for resolution of symptoms and adverse effects (e.g., diarrhea, rash). - **Clinical Signs**: Watch for signs of C. difficile infection (persistent diarrhea), allergic reactions (rash, dyspnea), or superinfections. ## Clinical Pearls - 💡 **Administration**: Can be taken with food to reduce GI upset. - 💡 **Cross-Reactivity**: Low risk (1-5%) of cross-reactivity with penicillin allergy, but avoid in severe penicillin allergy. - 💡 **Not for MRSA**: Cephalexin is primarily active against gram-positive organisms, but not methicillin-resistant Staphylococcus aureus (MRSA). - 💡 **Storage**: Oral suspension requires refrigeration and should be discarded after 14 days. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.