QAre routine labs for terbinafine needed?

A
Gabriela Maloney, DO

Gabriela Maloney, DO

Dermatologist
Forefront Dermatology
Brookfield, WI

Oral terbinafine has been available in the United States since 1996. It is FDA approved for dermatophyte onychomycosis and tinea capitis. It is fungistatic, and is detected on the nails for 30 and 36 weeks after completion of a 6 and 12 week long therapy, respectively. Terbinafine has a significant first pass hepatic metabolism and about 70% of the drug is excreted by the kidneys (1). About 3.3% of patients have an increase in their LFTs of equal to or greater than twice the upper limit of normal (1) and some cases of rhabdomyolysis have been reported (3). These have been reported to develop within 4-6 weeks of treatment.  Rare cases of severe neutropenia, thrombocytopenia, agranulocytosis, pancytopenia, and anemia have occurred. Altered prothrombin time with warfarin has also been reported (1).

Most sources recommend baseline LFTs, along with repeat LFTs when treatment is expected to last 6 weeks or longer (1). A CBC should be considered in patients with known or suspected immunodeficiency, but there are no official guidelines regarding monitoring for potential blood discrasias (3).

Some studies have questioned the need for laboratory monitoring with terbinafine in healthy adults and children, claiming a very low rate of laboratory abnormalities and that monitoring would not prevent fulminant hepatic necrosis. These studies did not comment on baseline labs and still stated that pretreatment LFTs are advised (4). Because of the lack of guidelines stating that baseline and/or interval LFTs and CBC are not needed, I personally still order baseline CBC and LFTs and repeat these tests at 6 weeks. I will order a CMP is there is a question regarding potential renal dysfunction. Most patients are very accepting of the extra testing and some even state they are more comfortable having close blood monitoring.

References:

  1. Wolverton et al. Comprehensive Dermatologic Drugs.
  2. Lever LR, et al. How orally administered terbinafine reaches the stratum corneum. J Dermatol Treat. 1990. 1:23-5.
  3. Gupta et al. Terbinafine: an update. JAAD. 1997. 37;6:979-88.
  4. Stolmeier et al. Utility of laboratory test result monitoring in patients taking oral terbinafine or griseofulvin for dermatophyte infections. JAMA Dermatol 2018154: 1409-1416.