Generic Name

Terbinafine

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Classification

FDA Approved Indications

• Onychomycosis (nail fungus) caused by dermatophytes
• Superficial dermatophyte infections (tinea corporis, tinea cruris, tinea pedis)

Mechanism of Action

Inhibits fungal squalene epoxidase, leading to a decrease in ergosterol synthesis, an essential component of fungal cell membranes, resulting in cell death.

Dosage and Administration

Adult: 250 mg once daily for 6 weeks (finger nails) or 12 weeks (toe nails); topical formulations vary

Pediatric: Safety and efficacy not established in children under 4 years for topical use; consult specific product guidelines for other uses

Geriatric: Use with caution; adjust dose if necessary based on hepatic and renal function

Renal Impairment: No dosage adjustment for mild to moderate impairment; use caution in severe impairment

Hepatic Impairment: Avoid in active hepatic disease; monitor liver function closely if treatment is necessary

Pharmacokinetics

Absorption: Well absorbed from the gastrointestinal tract

Distribution: Widely distributed, including skin, nails, and adipose tissue; high affinity for keratinized tissue

Metabolism: Primarily via hepatic CYP450 enzymes (notably CYP2D6 and CYP1A2)

Excretion: Primarily through feces; minor amount in urine

Half Life: Approximately 36 hours

Contraindications

• Hypersensitivity to terbinafine or any component of the formulation

Precautions

• Liver disease, or history of hepatic impairment; monitor liver function during therapy
• Use caution in patients with autoimmune diseases or hematologic disorders

Adverse Reactions - Common

• Gastrointestinal disturbances (dyspepsia, diarrhea) (Common)
• Headache (Common)
• Rash, pruritus (Common)

Adverse Reactions - Serious

• Hepatotoxicity (elevated liver enzymes, hepatitis, failure) (Rare but serious)
• Taste disturbance (dysgeusia) (Uncommon)
• Stevens-Johnson syndrome, toxic epidermal necrolysis (Rare)

Drug-Drug Interactions

• CYP450 inhibitors or inducers (e.g., cimetidine, rifampin, ketoconazole) may alter terbinafine levels

Drug-Food Interactions

• Limited data, generally none significant

Drug-Herb Interactions

• Avoid herbal preparations that may affect CYP450 enzymes

Nursing Implications

Patient/Family Teaching

• Complete full course of therapy even if symptoms improve
• Report signs of hepatotoxicity (jaundice, dark urine, fatigue)
• Avoid alcohol during treatment
• Inform about possible taste disturbances

Special Considerations

Black Box Warnings:

• Hepatotoxicity: Liver damage has been reported; monitor liver function closely

Genetic Factors: No known significant genetic factors affecting response

Lab Test Interference: May cause elevated hepatic enzymes; interpret with caution

Overdose Management

Signs/Symptoms: Gastrointestinal symptoms, dizziness, headache, hypersensitivity reactions

Treatment: Supportive care; no specific antidote; consult poison control for management

Storage and Handling

Storage: Store at 20-25°C (68-77°F), protected from moisture and light

Stability: Stable under recommended conditions for the duration of the expiration date