What laboratory tests are recommended before prescribing terbinafine (antifungal medication) to a 14-year-old patient?

Laboratory Tests Required Before Prescribing Terbinafine to a 14-Year-Old

Baseline liver function tests and a complete blood count are required before prescribing terbinafine to a 14-year-old patient, as it is unlicensed for use in children and carries potential hepatotoxicity risks. 1

Required Laboratory Tests

• Liver Function Tests (LFTs): Essential baseline testing due to the potential for hepatotoxicity, which can occur in patients with and without pre-existing liver disease 2
• Complete Blood Count (CBC): Required to establish baseline hematological parameters before initiating therapy 1

Rationale for Laboratory Monitoring

• Terbinafine is not licensed for pediatric onychomycosis, making baseline testing particularly important in this age group 1
• The British Association of Dermatologists explicitly recommends these tests for pediatric patients receiving terbinafine 1
• FDA labeling states that liver function tests should be performed before prescribing terbinafine tablets due to potential hepatotoxicity 2
• Hematological abnormalities, including neutropenia, have been reported with terbinafine use, necessitating baseline CBC 2

Dosing Considerations for 14-Year-Olds

• For a 14-year-old patient weighing >40 kg, the recommended dose is 250 mg per day 1
• Treatment duration depends on infection site: 6 weeks for fingernail infections and 12 weeks for toenail infections 1

Monitoring During Treatment

• Patients should be instructed to report immediately any symptoms of liver dysfunction including:
  • Persistent nausea, anorexia, fatigue, vomiting
  • Right upper abdominal pain or jaundice
  • Dark urine or pale stools 2
• Consider periodic monitoring of liver function during treatment, especially if treatment extends beyond the standard duration 2
• Monitor for taste disturbances, which can be severe and potentially permanent 3, 2

Clinical Considerations and Cautions

• Terbinafine is contraindicated in patients with hepatic impairment 1
• While mild laboratory abnormalities are relatively common (occurring in about 20% of pediatric patients), significant abnormalities requiring discontinuation are rare 4
• Terbinafine is generally well-tolerated in children, with adverse reactions occurring in approximately 5-10% of pediatric patients 5

Alternative Options

• If laboratory tests reveal pre-existing liver or hematological abnormalities, consider alternative antifungals such as itraconazole or topical treatments 1
• For patients unable to tolerate oral antifungals, topical options like amorolfine or ciclopirox may be considered 1