A new article in the JAMA Archives of Dermatology states: "The risk for clinically apparent liver injury from oral terbinafine has been greatly exaggerated and occurs in as few as 1 in 50,000 to 100,000 treatments, with even rarer instances of durable clinical sequelae."
See: MedScape Commentary
and Kanzler MH. Reevaluating the need for laboratory testing in the treatment of onychomycosis: safety and cost-effectiveness considerations. JAMA Dermatol. 2016;152:263-264. Full Article.