Table 4.

Classification of Agents by Likelihood of Causing Liver Injury

Score	Descriptor	Definition
A	Known	Agent is well-established cause of hepatotoxicity; at least 50 cases are reported in the literature, some in case series (e.g., phenytoin, isoniazid, and amiodarone).
B	Rare	Agent has been implicated in causing hepatotoxicity; there are at least 10 but fewer than 50 cases in the literature, some in small case series (e.g., celecoxib, doxycycline, and atorvastatin).
C	Very rare	Agent has been rarely implicated in causing hepatotoxicity, with fewer than 10 but at least 3 convincing cases in the literature (e.g., metformin and metronidazole).
D	Unproven	Agent has been implicated in isolated case reports as causing liver injury, but there are fewer than 3 convincing cases in the literature (e.g., vancomycin and theophylline).
E	Not implicated	Agent has not been convincingly implicated in cases of liver injury (e.g., folic acid and hydrochlorothiazide).
X	Insufficient information	Agent has not been available for long enough or used in enough patients to judge its hepatotoxic potential (e.g., febuxostat, etravirine, and iloperidone).