Lamisil (Terbinafine)

Lamisil (terbinafine) is used to treat fungal infections of the skin and nails caused by dermatophytes.

• Tinea pedis (athlete’s foot): reduces itching and clears the infection of the foot skin.
• Tinea corporis (ringworm): eliminates the fungal lesions on the body.
• Tinea cruris (jock itch): resolves inflammation and scaling in the groin area.
• Onychomycosis (fungal nail infection): improves nail appearance and eradicates the causative fungus.

• Terbinafine acts by inhibiting the fungal enzyme squalene epoxidase, a key step in ergosterol biosynthesis. Blockade of this enzyme leads to intracellular accumulation of squalene, which is toxic to the fungus, and a depletion of ergosterol, an essential component of the fungal cell membrane, ultimately causing cell death. The selective inhibition spares human cells because the target enzyme is absent in mammalian cholesterol pathways, providing a high therapeutic index for systemic treatment.

Terbinafine may cause a range of adverse reactions, varying from mild to severe.

Common Side Effects

• Gastrointestinal discomfort: nausea, abdominal pain or diarrhea.
• Headache: mild to moderate intensity.
• Skin rash: localized erythema or pruritus.
• Taste disturbance: temporary loss or alteration of taste.
• Elevated liver enzymes: mild, transient increase detected in lab tests.
• Dizziness: occasional light‑headedness.

Serious or Rare Side Effects

• Hepatotoxicity: severe liver injury or hepatitis.
• Severe cutaneous reactions: Stevens‑Johnson syndrome or toxic epidermal necrolysis.
• Blood dyscrasias: agranulocytosis, aplastic anemia.
• Persistent taste loss: prolonged dysgeusia affecting nutrition.
• Peripheral neuropathy: rare nerve damage.

Before prescribing terbinafine, clinicians should consider several safety precautions.

• Liver function monitoring: assess baseline hepatic enzymes and repeat during therapy.
• Hypersensitivity caution: avoid in patients with known allergy to terbinafine or other allylamines.
• Concomitant hepatotoxic drugs: use with caution when combined with other agents that affect liver.
• Renal impairment: dose adjustment may be required in severe renal dysfunction.
• Pregnancy and lactation: evaluate risk‑benefit; use only if clearly needed.
• Store below 25°C: keep in the original packaging, protect from moisture and light.

Terbinafine can interact with other medicines, altering its concentration or that of the co‑administered drug.

Major Interactions (Avoid)

• Cimetidine: may increase terbinafine plasma levels, raising toxicity risk.
• Itraconazole: combined use can lead to hepatic injury.
• Ritonavir (and other strong CYP3A4 inhibitors): significantly raise terbinafine exposure.

Moderate Interactions (Monitor Closely)

• Warfarin: terbinafine may enhance anticoagulant effect, requiring INR monitoring.
• Oral contraceptives: efficacy may be reduced, consider alternative contraception.
• Cyclosporine: increased risk of nephrotoxicity; monitor renal function.