Rhabdomyolysis attributed to terbinafine: A rare occurrence that can be mistaken for terbinafine-induced hepatotoxicity

Terbinafine is a common antifungal medication taken orally to treat onychomycosis. This drug is considered a first-line agent for this disease and has a better cure rate than other antifungal drugs.1 Terbinafine functions as an allylamine agent, which inhibits squalene epoxidase, a key enzyme of ergosterol biosynthesis. The increase in concentration of extracellular squalene is thought to result in toxic levels that kill fungal cells.2 Side effects of terbinafine include gastrointestinal disturbances, dysgeusia, headache, and rash.1 Hepatotoxicity is a less frequent adverse effect of terbinafine that has an incidence of 2.5 cases/100,000.3 Because of the potential for this feared adverse event, some physicians have chosen to monitor liver enzymes during the course of terbinafine treatment. Rhabdomyolysis is another rare side effect that has been associated with terbinafine use. Many occurrences have been reported by physicians in adverse drug reaction reporting databases; however, there have been few published cases of this association.4, 5 Because rhabdomyolysis is not a well-known side effect of terbinafine, patients might not readily discuss symptoms of weakness, myalgia, or darkened urine. Elevated liver enzymes found on routine monitoring might also mistakenly be attributed to terbinafine-induced hepatotoxicity. As a result, it is important to have rhabdomyolysis as a differential diagnosis when monitoring patients on terbinafine.