Keflex (Cephalexin) is NOT Appropriate for Nail Infections
Cephalexin has no role in the treatment of onychomycosis (nail fungal infections) and should not be prescribed for this indication. Nail infections are caused by fungi, not bacteria, and require antifungal therapy—not antibiotics like cephalexin 1, 2.
Why Cephalexin is Inappropriate
- Cephalexin is an antibiotic that targets bacterial infections of skin and soft tissues, respiratory tract, and urinary tract infections 3, 4
- Onychomycosis is a fungal infection caused by dermatophytes (most common), yeasts, or non-dermatophyte molds 1
- Antibiotics have zero antifungal activity and will not eradicate fungal pathogens from nail tissue 1
Correct First-Line Treatment for Nail Infections
Oral terbinafine 250 mg once daily is the first-line treatment for onychomycosis, based on superior efficacy and tolerability compared to all alternatives 1, 2, 5.
Dosing by Nail Location
- Fingernail infections: Terbinafine 250 mg daily for 6 weeks 1, 5
- Toenail infections: Terbinafine 250 mg daily for 12 weeks (up to 16 weeks for severe cases) 1, 5
- Both fingernails and toenails simultaneously: Treat for 12 weeks, which adequately covers both 2
Pre-Treatment Requirements
Before prescribing terbinafine, obtain 1, 5, 6:
- Baseline liver function tests (LFTs)
- Complete blood count (CBC)
- Mycological confirmation (microscopy and culture) to confirm fungal infection and identify the causative organism
Contraindications to Terbinafine
Do not prescribe terbinafine in patients with 1, 5, 6:
- Active or chronic liver disease
- Lupus erythematosus
- Severe renal impairment
Why Terbinafine is Superior
- Complete cure rate of 55% at 72 weeks versus 26% with itraconazole 1, 2
- Long-term mycological cure of 46% at 5 years without retreatment versus 13% with itraconazole 1, 2
- Fungicidal activity with very low minimum inhibitory concentrations (0.004 μg/mL) against dermatophytes 1, 5
- Minimal drug interactions compared to azole antifungals, only requiring caution with CYP2D6 substrates 2, 5, 6
Second-Line Alternatives (If Terbinafine Contraindicated)
Itraconazole
- Dosing: 200 mg daily for 12 weeks continuously, OR pulse therapy 400 mg daily for 1 week per month (2 pulses for fingernails, 3 pulses for toenails) 1, 2
- Caution: Contraindicated in heart failure; significant drug interactions via CYP3A4 inhibition 1
Fluconazole (Third-Line)
- Dosing: 450 mg once weekly for 3 months (fingernails) or at least 6 months (toenails) 1, 2
- Lower efficacy than terbinafine or itraconazole, but convenient once-weekly dosing 1, 2
Common Pitfall to Avoid
Do not confuse bacterial paronychia (nail fold infection) with onychomycosis (nail plate infection). Acute bacterial paronychia presents with acute pain, erythema, and purulent drainage around the nail fold and may warrant antibiotics like cephalexin 3. However, chronic nail plate thickening, discoloration, and subungual debris indicate fungal onychomycosis requiring antifungal therapy 1.