What is the recommended treatment regimen for a patient with a fungal infection using Terbinafine (antifungal medication)?

Terbinafine Treatment Regimen

Terbinafine dosing depends critically on the type and location of fungal infection, with treatment duration ranging from 2-4 weeks for tinea capitis (Trichophyton species) to 12 weeks for toenail onychomycosis. 1, 2

Onychomycosis (Nail Infections)

For toenail onychomycosis, prescribe terbinafine 250 mg once daily for 12 weeks (up to 16 weeks for severe cases). 2, 3 For fingernail onychomycosis, the duration is shorter at 6 weeks. 2, 4

• The optimal clinical effect appears months after treatment cessation due to the time required for healthy nail outgrowth 4
• Terbinafine persists in nail tissue for up to 30 weeks after treatment completion, allowing continued fungicidal activity 2, 3
• Complete cure rates at 72 weeks reach 55% versus 26% for itraconazole, establishing terbinafine as superior first-line therapy 2

Mandatory Pre-Treatment Requirements for Onychomycosis

• Confirm mycological diagnosis with both microscopy and culture before prescribing 2
• Obtain baseline liver function tests (ALT and AST) and complete blood count 2, 4
• These laboratory tests are particularly critical in patients with history of hepatitis, heavy alcohol use, or hematological abnormalities 3

Tinea Capitis (Scalp Ringworm)

The causative organism determines treatment choice: terbinafine is highly effective for Trichophyton species but significantly inferior for Microsporum species, where griseofulvin is preferred. 1

Pediatric Weight-Based Dosing for Tinea Capitis

• < 20 kg: 62.5 mg daily for 2-4 weeks 1
• 20-40 kg: 125 mg daily for 2-4 weeks 1
• > 40 kg: 250 mg daily for 2-4 weeks 1

Critical Species-Specific Considerations

• For Trichophyton infections (T. tonsurans, T. violaceum, T. soudanense), terbinafine achieves 94% efficacy with 2-3 weeks of treatment 1, 5
• For Microsporum infections (M. canis, M. audouinii), switch to griseofulvin 15-20 mg/kg/day for 6-8 weeks, as terbinafine's minimum inhibitory concentration exceeds achievable hair concentrations 1
• Terbinafine is not excreted in sweat or sebum of prepubertal children and cannot be incorporated into hair shafts, explaining its relative inefficacy against Microsporum 1

Tinea Pedis and Tinea Corporis/Cruris (Skin Infections)

For dermatophyte foot and body infections, prescribe terbinafine 250 mg daily for 1-2 weeks, achieving mycological cure rates of 80-90%. 6, 7, 8

• Topical terbinafine 1% cream applied twice daily for up to 2 weeks is equally effective for localized infections 7, 9
• Oral therapy is superior to topical for extensive or recalcitrant cases 9

Absolute Contraindications

Do not prescribe terbinafine in patients with active or chronic liver disease or lupus erythematosus. 3, 4

Additional contraindications include:

• Known hypersensitivity to oral terbinafine 4
• Porphyria 1

Critical Safety Monitoring During Treatment

Instruct patients to immediately report persistent nausea, anorexia, fatigue, vomiting, right upper abdominal pain, jaundice, dark urine, or pale stools—discontinue terbinafine immediately if these occur. 2, 4

Additional serious adverse effects requiring immediate discontinuation:

• Taste or smell disturbance (may become permanent) 4
• Depressive symptoms (feel sad/worthless, sleep changes, loss of energy) 4
• Serious skin reactions (rash, hives, mouth sores, blistering/peeling skin, facial swelling) 4
• New or worsening lupus symptoms (erythema, scaling, pigment loss, photosensitivity) 4

Most common adverse effects include gastrointestinal disturbances (49% of reported side effects), headache, and rash, with serious adverse events occurring in only 0.04% of patients 3, 7

Drug Interactions

Terbinafine has minimal drug-drug interactions compared to azole antifungals, making it safer for patients on multiple medications. 3

The only potentially significant interaction involves drugs metabolized by cytochrome P450 2D6:

• Certain antidepressants, beta-blockers, and antiarrhythmics 3
• Desipramine specifically mentioned 4
• Plasma concentration decreased by rifampin and increased by cimetidine 1

Terbinafine is preferred in diabetic and immunosuppressed patients due to low hypoglycemia risk and minimal interactions with antiretrovirals and immunosuppressive medications. 2, 6

Treatment Failure Management

If the first course fails, restart terbinafine 250 mg daily for the full duration without additional waiting period. 2, 3

• Re-evaluate patients 3-6 months after treatment initiation with mycological analysis and clinical examination 2, 3
• If the second terbinafine course fails, switch to itraconazole 200 mg daily for 12 weeks continuously, or 400 mg daily for 1 week per month for 3 cycles 2, 3
• Consider fluconazole 450 mg weekly for at least 6 months if intolerance to both terbinafine and itraconazole occurs 3

Practical Administration Details

• Terbinafine can be taken with or without food 2, 3
• If a dose is forgotten, take as soon as remembered unless less than 4 hours before the next dose 4
• A granule formulation (125 mg or 187.5 mg packets to sprinkle on food) is available in the U.S. for children > 4 years but remains unlicensed in the U.K. 1

Special Populations

Pregnancy and Breastfeeding: Do not start terbinafine during pregnancy without discussing with the patient, as safety is unknown; terbinafine passes into breast milk and may harm the baby 4

Photosensitivity: Advise patients to minimize exposure to natural and artificial sunlight (tanning beds, UVA/B treatment) while using terbinafine 4