Generic Name

Terbinafine Hydrochloride

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Classification

FDA Approved Indications

• Onychomycosis (nail fungus)
• Tinea corporis (ringworm), Tinea cruris (jock itch), Tinea pedis (athlete's foot)

Mechanism of Action

Inhibits fungal squalene epoxidase, leading to accumulation of squalene and inhibition of fungal ergosterol synthesis, disrupting cell membrane formation.

Dosage and Administration

Adult: 250 mg once daily for 6 weeks (onychomycosis fingernails) or 12 weeks (toenails).

Pediatric: Not generally recommended; consult guidelines.

Geriatric: Adjust based on renal and hepatic function, start at lower doses if needed.

Renal Impairment: Use with caution, adjust dose as needed.

Hepatic Impairment: Contraindicated in active liver disease; monitor liver function.

Pharmacokinetics

Absorption: Well absorbed orally, with increased absorption when taken with food.

Distribution: Extensively distributed in body tissues, especially keratin-containing tissues.

Metabolism: Hepatically metabolized via CYP enzymes, notably CYP2C9 and CYP1A2.

Excretion: Primarily via the urine (metabolites), small amount as unchanged drug in feces.

Half Life: approximately 200-400 hours (due to tissue accumulation).

Contraindications

• Active liver disease
• Hypersensitivity to terbinafine

Precautions

• Monitor liver function during therapy.
• Use with caution in hepatic impairment, and in patients taking other hepatotoxic drugs.

Adverse Reactions - Common

• Gastrointestinal upset (dyspepsia, diarrhea) (Common)
• Headache (Common)
• Dizziness (Common)

Adverse Reactions - Serious

• Hepatotoxicity (liver failure) (Rare, but potentially serious)
• Stevens-Johnson Syndrome or Toxic Epidermal Necrolysis (Rare)

Drug-Drug Interactions

• CYP2C9 inhibitors or inducers may alter levels of terbinafine.

Drug-Food Interactions

N/A

Drug-Herb Interactions

N/A

Nursing Implications

Patient/Family Teaching

• Take medication with food to reduce gastrointestinal upset.
• Report signs of liver problems (jaundice, dark urine, severe fatigue).
• Complete full course of therapy even if symptoms resolve.
• Avoid alcohol and hepatotoxic substances.

Special Considerations

Black Box Warnings:

• Hepatotoxicity is rare but serious; monitor liver function.

Genetic Factors: Genetic polymorphisms may affect metabolism, but not routinely tested.

Lab Test Interference: May slightly affect liver function tests.

Overdose Management

Signs/Symptoms: Nausea, vomiting, headache, dizziness, abdominal pain.

Treatment: Supportive care; no specific antidote. Hemodialysis not effective due to extensive tissue binding.

Storage and Handling

Storage: Store at room temperature, 20-25°C (68-77°F).

Stability: Stable under recommended storage conditions for the shelf life indicated.