What it's for (Indications)
- Terbinafine, exemplified by brand names such as Exinofin, is an allylamine antifungal agent primarily indicated for the treatment of dermatophyte infections.
- Orally administered terbinafine is extensively used for onychomycosis of the toenail or fingernail, caused by tinea unguium (dermatophytes such as *Trichophyton rubrum*, *Trichophyton mentagrophytes*, and *Epidermophyton floccosum*).
- It is also indicated for the treatment of tinea capitis in pediatric patients, as well as severe or extensive tinea corporis, tinea cruris, and tinea pedis that are unresponsive to appropriate topical therapy.
- Topical formulations are available for less severe superficial fungal infections.
- The decision for systemic therapy often hinges on the extent and severity of the infection, presence of immunodeficiency, and documented failure of topical agents, underscoring its role in advanced mycotic conditions.
Dosage Information
| Type | Guideline |
|---|---|
| Standard | The dosage of oral terbinafine varies based on the specific fungal infection and patient population. For onychomycosis of the fingernails, the typical adult dosage is 250 mg once daily for a duration of 6 weeks. For onychomycosis of the toenails, the recommended adult dosage is 250 mg once daily for a more extended period of 12 weeks. Strict adherence to the prescribed treatment duration is crucial for achieving optimal mycological cure and preventing recurrence, and patients should be thoroughly counselled on compliance. For tinea capitis in pediatric patients, dosing is weight-based, generally 125 mg once daily for children weighing less than 25 kg, 187.5 mg once daily for children weighing 25-35 kg, and 250 mg once daily for children weighing over 35 kg, typically administered for 2 to 4 weeks. For other severe dermatophyte infections, such as extensive tinea corporis or tinea cruris, a dosage of 250 mg once daily for 2 to 4 weeks is common. Terbinafine may be taken with or without food, though some studies suggest absorption may be slightly enhanced with meals. |
Safety & Warnings
Common Side Effects
- Common side effects associated with oral terbinafine include a range of gastrointestinal disturbances such as diarrhea, nausea, dyspepsia, and mild abdominal pain, affecting a notable percentage of patients.
- Dermatological reactions like rash and pruritus are also frequently reported, usually mild and transient.
- A distinctive and often reversible side effect is taste disturbance, including taste loss (ageusia) or altered taste sensation (dysgeusia), which can impact patient compliance, appetite, and nutritional intake.
- Less commonly, patients may experience headache, dizziness, arthralgia, myalgia, or transient liver enzyme elevations, which typically normalize upon cessation of treatment.
- Serious, albeit rare, adverse effects include severe hepatotoxicity (ranging from cholestatic hepatitis to hepatic failure and death), severe dermatologic reactions (e.
- g.
- , Stevens-Johnson syndrome, toxic epidermal necrolysis, erythema multiforme, acute generalized exanthematous pustulosis), and various hematologic disorders (e.
- g.
- , neutropenia, agranulocytosis, pancytopenia, thrombocytopenia).
- Vigilant monitoring for these serious events is critical throughout the duration of therapy.
Serious Warnings
- Black Box Warning: Terbinafine does not currently carry an FDA-mandated Black Box Warning. However, it is associated with several serious potential risks that warrant significant caution and vigilant monitoring, effectively serving as a 'Serious Warnings' section. These include rare but severe cases of hepatotoxicity, which can manifest as cholestatic hepatitis, hepatic failure, and, in isolated instances, death. Patients should be thoroughly informed about the signs and symptoms of liver dysfunction (e.g., persistent nausea, anorexia, unexplained fatigue, dark urine, jaundice, right upper quadrant pain) and explicitly instructed to seek immediate medical attention if any of these occur. Baseline and periodic monitoring of liver function tests (LFTs) is strongly recommended, particularly for patients on prolonged treatment courses or with pre-existing risk factors. Additionally, severe dermatologic reactions, such as Stevens-Johnson syndrome and toxic epidermal necrolysis, as well as various hematologic abnormalities (e.g., neutropenia, agranulocytosis, pancytopenia), have been reported. Although uncommon, these events can be life-threatening and require immediate discontinuation of the drug and appropriate medical management. Patients should be advised to promptly report any new or worsening symptoms.
- Terbinafine use necessitates careful consideration due to potential serious adverse effects, particularly hepatotoxicity.
- Patients should undergo baseline liver function tests (LFTs) including serum transaminases and bilirubin before initiating treatment and periodic monitoring during therapy, especially for those on prolonged courses or with pre-existing liver conditions.
- If signs or symptoms suggestive of liver dysfunction develop (e.
- g.
- , persistent nausea, anorexia, unexplained fatigue, dark urine, jaundice, right upper quadrant pain), the drug should be immediately discontinued, and LFTs performed promptly for evaluation.
- Rare but severe dermatologic reactions, including Stevens-Johnson syndrome and toxic epidermal necrolysis, have been reported; patients should be advised to seek immediate medical attention for widespread rash, blistering, or mucocutaneous lesions.
- Hematologic abnormalities, such as neutropenia and agranulocytosis, although uncommon, warrant immediate discontinuation if symptomatic.
- Terbinafine should be used with caution in patients with impaired renal function (creatinine clearance less than 50 mL/min) as its elimination may be reduced, and a dose reduction should be considered.
- Drug interactions are also clinically relevant, especially with potent inhibitors of CYP2D6 (e.
- g.
- , cimetidine, fluoxetine, amiodarone), which can significantly increase terbinafine plasma levels, and concomitant use requires caution.
- Similarly, CYP2D6 inducers may decrease terbinafine concentrations.
How it Works (Mechanism of Action)
Terbinafine exerts its potent antifungal activity by selectively interfering with fungal ergosterol biosynthesis, a vital component of the fungal cell membrane. Specifically, it functions as a non-competitive inhibitor of squalene epoxidase, an enzyme integral to the early stages of the ergosterol synthesis pathway. This inhibition leads to a dual fungicidal effect: first, it causes an intracellular accumulation of squalene within the fungal cell, which is toxic and disrupts membrane function. Second, it results in a profound deficiency of ergosterol, thereby compromising the structural integrity, fluidity, and permeability of the fungal cell membrane. The combined action of squalene accumulation and ergosterol depletion leads to fungal cell death, rendering terbinafine a fungicidal agent primarily against dermatophytes. Its selectivity arises from its higher affinity for fungal squalene epoxidase compared to the corresponding mammalian enzyme, contributing to its favorable therapeutic index in humans.