TERBIDERM FORTE TABLETS

Indications

• Onychomycosis (fungal nail infections)
• Tinea pedis (athlete's foot)
• Tinea corporis (ringworm)
• Tinea cruris (jock itch)
• Tinea capitis (scalp ringworm)
• Other dermatophyte infections

Dosage

Children: Refer to the BNF for Children for specific dosing recommendations in paediatric patients.

Adults: For onychomycosis, the usual oral dose is 250 mg once daily for 6 weeks for fingernails and 12 weeks for toenails. For other dermatophyte infections, dosing may vary, refer to specific guidelines.

Mechanism of action

Terbinafine selectively inhibits the enzyme squalene epoxidase, which plays a crucial role in the biosynthesis of ergosterol. By blocking this enzyme, terbinafine disrupts the production of ergosterol, resulting in an accumulation of toxic squalene and ultimately causing fungal cell death.

Pharmacodynamics

Terbinafine exhibits fungicidal activity against a wide range of dermatophytes, yeasts, and some molds. Its action is primarily against dermatophytes, which are responsible for most superficial fungal infections. The drug has a high affinity for keratin, which allows it to accumulate in skin, hair, and nails, enhancing its effectiveness in treating infections in these tissues.

Pharmacokinetics

Terbinafine is well absorbed following oral administration, with peak plasma concentrations occurring within 2 hours. It has a bioavailability of around 40% due to first-pass metabolism. The drug is extensively distributed in body tissues, particularly in skin and nails, and is metabolized primarily in the liver via cytochrome P450 enzymes. The elimination half-life is approximately 36 hours, allowing for once-daily dosing. Terbinafine is excreted mainly in urine, with a small percentage eliminated in feces.

Contra-indications

• Hypersensitivity to terbinafine or any of the excipients
• Active or chronic liver disease
• Severe renal impairment

Adverse effects

• Gastrointestinal disturbances (nausea, diarrhea, abdominal pain)
• Headache
• Dizziness
• Rash
• Pruritus
• Altered liver function tests
• Taste disturbances (dysgeusia)
• Skin reactions (urticaria, erythema multiforme)
• Rarely, hepatotoxicity and severe skin reactions (Stevens-Johnson syndrome)

Interactions

• Caution with concomitant use of CYP2D6 substrates, as terbinafine can inhibit this enzyme
• May increase plasma concentrations of certain medications metabolized by the liver
• Caution with other hepatotoxic drugs

Precautions

• Monitor liver function tests before and during treatment, especially in patients with pre-existing liver conditions
• Use with caution in patients with a history of alcohol abuse
• Discontinue if signs of liver dysfunction or severe skin reactions occur

Pregnancy

Terbinafine should only be used during pregnancy if the potential benefit justifies the potential risk to the fetus. It is not recommended as a routine treatment in pregnant women.

Breast-feeding

Terbinafine is excreted in breast milk. Caution is advised when administering to nursing women, and alternative treatments may be considered.

Storage

Store at room temperature, away from light and moisture. Keep out of reach of children.

Formulations

• Tablets (250 mg)
• Cream (1%)
• Spray (1%)
• Solution (1%)