What to check before and after starting terbinafine (Lamisil) for fungal nail infections?

Pre- and Post-Treatment Monitoring for Terbinafine (Lamisil)

Before starting terbinafine for fungal nail infections, baseline liver function tests and a complete blood count should be performed in patients with a history of heavy alcohol consumption, hepatitis, or hematological abnormalities, as well as in children since the medication is not licensed for pediatric onychomycosis. 1

Pre-Treatment Evaluation

Required Testing

• Nail specimen collection for laboratory testing (KOH preparation, fungal culture, or nail biopsy) to confirm onychomycosis diagnosis 2
• Baseline liver function tests for:
  • Patients with history of heavy alcohol consumption
  • History of hepatitis
  • Pre-existing hematological abnormalities
  • Children (as terbinafine is not licensed for pediatric use)
  • Patients with pre-existing liver disease 1, 3
• Complete blood count for high-risk patients 1

Contraindications Assessment

• Active or chronic liver disease (terbinafine is contraindicated) 1, 3
• Review of current medications for potential CYP2D6 interactions:
  • Tricyclic antidepressants
  • Some cardiovascular drugs
  • Desipramine
  • Cyclosporine 3, 2

Patient Education Before Starting Treatment

Patients should be informed about:

• Treatment duration: 6 weeks for fingernails, 12-16 weeks for toenails 1, 2
• Common side effects:
  • Gastrointestinal issues (49% of patients) - nausea, diarrhea
  • Dermatological reactions (23% of patients) - rash, pruritus, urticaria 1, 3
• Rare but serious adverse effects to watch for:
  • Taste disturbance (can be permanent)
  • Stevens-Johnson syndrome
  • Toxic epidermal necrolysis
  • Hepatotoxicity 1, 3, 2
• Signs requiring immediate medical attention:
  • Persistent nausea, anorexia, fatigue, vomiting
  • Right upper abdominal pain, jaundice
  • Dark urine or pale stools
  • Hives, mouth sores, blistering/peeling skin
  • Swelling of face, lips, tongue, or throat
  • Difficulty swallowing or breathing 2

Post-Treatment Monitoring

Clinical Follow-up

• Re-evaluation at 3-6 months after treatment initiation 1
• Assessment for clinical response (nail clearing)
• Consideration for additional treatment if disease persists 1

Monitoring for Adverse Effects

• Liver function monitoring for patients:
  • With pre-existing abnormal liver function tests
  • Receiving continuous therapy for more than a month
  • Taking concomitant hepatotoxic drugs 3
• Monitoring for symptoms of:
  • Hepatotoxicity (as described above)
  • Taste or smell disturbances
  • Depressive symptoms
  • Signs of lupus erythematosus (erythema, scaling, loss of pigment)
  • Photosensitivity reactions 3, 2

Special Considerations

Elderly Patients

• Generally well-tolerated in patients ≥65 years, even with concomitant medications
• No significant increase in adverse events compared to younger patients
• No clinical signs of drug interactions observed with common medications like antihypertensives, antidiabetics, or lipid-lowering agents 4

Liver Disease

• In cases where terbinafine must be used in patients with stable liver disease:
  • Consider consultation with a hepatologist
  • Limit exposure to less than 6 weeks
  • Monitor liver function tests more frequently
  • Provide thorough patient education on signs of liver injury 5

Common Pitfalls to Avoid

1. Failing to confirm diagnosis before treatment - always obtain appropriate nail specimens for laboratory testing 2
2. Not checking baseline liver function in high-risk patients 1, 3
3. Overlooking potential drug interactions with medications metabolized by CYP2D6 3
4. Inadequate patient education about serious adverse effects requiring immediate medical attention 2
5. Not monitoring for taste disturbances which, though rare, can become permanent 1, 2

Terbinafine remains the first-line treatment for dermatophyte onychomycosis due to its superior efficacy compared to itraconazole and other antifungals, with generally good tolerability and low potential for drug interactions 1, 6.