Do you need to check liver enzymes before beginning terbinafine (Lamisil) therapy?

Baseline Liver Enzyme Testing Before Terbinafine

Yes, you must check liver function tests (ALT and AST) before starting terbinafine in all patients, as explicitly mandated by the FDA drug label. 1

FDA-Mandated Baseline Testing

• The FDA prescribing information states: "Measurement of serum transaminases (ALT and AST) is advised for all patients before taking terbinafine tablets." 1
• This recommendation applies universally because hepatotoxicity can occur in patients both with and without pre-existing liver disease 1
• Cases of liver failure leading to transplant or death have been documented with terbinafine use 1

Risk-Stratified Approach to Baseline Testing

Standard Patients

• Baseline liver function tests (LFTs) and complete blood count (CBC) are required before initiating therapy 2, 1

High-Risk Patients Requiring Mandatory Testing

• Patients with history of heavy alcohol consumption must have baseline LFTs and CBC 2
• Patients with history of hepatitis require baseline monitoring 2
• Patients with hematological abnormalities need baseline CBC and LFTs 2
• Pediatric patients should have baseline testing due to unlicensed use in children and heightened hepatotoxicity concerns 3

Contraindications Identified by Baseline Testing

• Terbinafine is contraindicated in patients with active or chronic liver disease 2, 1
• Hepatic impairment is an absolute contraindication 2
• Renal impairment also contraindicates terbinafine use 2

Clinical Rationale for Universal Baseline Testing

• The incidence of serious adverse events is 0.04%, but when hepatotoxicity occurs, outcomes can be catastrophic 2
• Hepatotoxicity typically develops 4-6 weeks after treatment initiation 4, 5
• Liver injury presents with both hepatocellular necrosis (elevated transaminases) and cholestatic features (elevated alkaline phosphatase) 4, 6
• Severe acute liver injury from terbinafine, while unusual, has been documented in systematic reviews 5

Ongoing Monitoring Considerations

• Periodic monitoring of liver function tests is recommended during treatment 1
• The British Association of Dermatologists recommends monitoring in patients receiving continuous therapy for more than one month 2
• More frequent monitoring is warranted for patients on concomitant hepatotoxic medications 2

Common Pitfalls to Avoid

• Failing to perform baseline LFTs in seemingly healthy patients is a critical error - the FDA mandates testing for all patients regardless of apparent health status 1
• Not educating patients about warning signs of hepatotoxicity (persistent nausea, anorexia, fatigue, vomiting, right upper abdominal pain, jaundice, dark urine, pale stools) before starting therapy 1
• Overlooking that taste and smell disturbances can be permanent, requiring patient counseling before initiation 2, 1
• Missing drug interactions with cytochrome P450 2D6 substrates 2

Patient Education Requirements

• Instruct patients to report immediately any symptoms of liver injury and discontinue terbinafine if these occur 1
• Warn about potentially permanent taste and smell disturbances that may develop 2, 1
• Advise patients to report skin reactions, as Stevens-Johnson syndrome and toxic epidermal necrolysis have been reported 2, 1