Terbinafine

# Terbinafine ## Overview - **Classification**: Antifungal, Allylamine - **Mechanism**: Inhibits squalene epoxidase, an enzyme in fungal sterol biosynthesis. This leads to squalene accumulation and ergosterol deficiency, disrupting fungal cell membrane function. ## Primary Indications 1. **Onychomycosis**: Fungal infection of fingernails or toenails. 2. **Tinea capitis**: Fungal infection of the scalp (primarily pediatric). 3. **Tinea corporis/cruris/pedis**: Extensive or recalcitrant fungal skin infections. ## Adult Dosing ### Standard Dosing **Onychomycosis (fingernails)** - **Dose**: **250 mg** - **Frequency**: Once daily (QD) - **Route**: Oral - **Duration**: **6 weeks** **Onychomycosis (toenails)** - **Dose**: **250 mg** - **Frequency**: Once daily (QD) - **Route**: Oral - **Duration**: **12 weeks** **Tinea corporis/cruris (extensive/recalcitrant)** - **Dose**: **250 mg** - **Frequency**: Once daily (QD) - **Route**: Oral - **Duration**: **2-4 weeks** **Tinea pedis (severe/hyperkeratotic)** - **Dose**: **250 mg** - **Frequency**: Once daily (QD) - **Route**: Oral - **Duration**: **2-6 weeks** ### Dose Adjustments - **Renal Impairment**: Not recommended if **CrCl < 50 mL/min**. - **Hepatic Impairment**: Not recommended due to increased risk of hepatotoxicity. - **Elderly Patients**: No specific dose adjustment; monitor renal/hepatic function. ## Pediatric Dosing ### Neonates (0-28 days) - **Dose**: Not recommended. - **Special Notes**: Safety and efficacy not established. Systemic use should be avoided. ### Infants (1-12 months) - **Dose**: Not routinely recommended. - **Special Notes**: Limited data; consultation with an infectious disease specialist is advised. ### Children (1-12 years) **Tinea capitis** (Primary indication for oral terbinafine in children) - **Dose**: Based on body weight (oral tablet, can be crushed): - **<25 kg**: **62.5 mg** QD - **25-40 kg**: **125 mg** QD - **>40 kg**: **250 mg** QD - **Frequency**: Once daily (QD) - **Route**: Oral - **Duration**: **6-8 weeks** (may vary based on clinical response) - **Maximum**: **250 mg/day** - **Special Notes**: Monitor LFTs throughout treatment. ### Adolescents (13-18 years) - **Dose**: Generally follows adult dosing guidelines. - **Frequency**: Once daily (QD) - **Route**: Oral - **Maximum**: **250 mg/day** - **Special Notes**: Consider adult weight threshold (e.g., >40 kg) for adult dosing. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to terbinafine. - **Absolute**: Active or chronic liver disease. - **Absolute**: Severe renal impairment (**CrCl < 50 mL/min**). ### Common Adverse Effects - **Very Common (>10%)**: Headache, GI upset (diarrhea, dyspepsia, nausea, abdominal pain). - **Common (1-10%)**: Rash, urticaria, arthralgia, myalgia, taste disturbance (dysgeusia/ageusia). - **Serious but Rare**: Hepatotoxicity (including liver failure), severe skin reactions (SJS, TEN), neutropenia, agranulocytosis, lupus-like syndrome. ### Key Drug Interactions - **CYP2D6 inhibitors (e.g., fluoxetine, paroxetine, amiodarone)**: May increase terbinafine levels; monitor for increased AEs. - **CYP2D6 substrates (e.g., TCAs, beta-blockers, antiarrhythmics)**: Terbinafine inhibits CYP2D6; may increase levels of co-administered drugs. Monitor for toxicity. - **Cimetidine**: May decrease terbinafine clearance; consider dose reduction of terbinafine. - **Rifampicin**: May increase terbinafine clearance; may reduce efficacy. ## Monitoring & Follow-up - **Before Treatment**: Baseline LFTs (ALT, AST), complete blood count (CBC). - **During Treatment**: Periodically monitor LFTs (e.g., at 4-6 weeks for onychomycosis). Monitor CBC for patients at risk or prolonged therapy. - **Clinical Signs**: Counsel patients to report persistent nausea, anorexia, dark urine, jaundice, pale stools, unusual fatigue (signs of liver dysfunction). Also fever, sore throat, or malaise (signs of blood dyscrasias). ## Clinical Pearls - 💡 **Tip 1**: Administer with food to reduce GI upset and improve tolerability. - 💡 **Tip 2**: Counsel patients on potential for taste disturbance, which can be prolonged and sometimes permanent. - 💡 **Tip 3**: Emphasize importance of completing the full prescribed course to prevent recurrence. - 💡 **Tip 4**: Oral terbinafine is generally well-tolerated but requires monitoring for rare, serious adverse effects. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.