Hy's law

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Hy's law is a rule of thumb that a drug is at high risk of causing a fatal drug-induced liver injury (DILI) when given to a large population, if it caused cases of liver injury that satisfied certain criteria when given to a smaller population. The law is based on observations by Hy Zimmerman, a major scholar of drug-induced liver injury.[1][2][3] Some have suggested the principle be called a hypothesis or observation.[4]

Hy's Law cases have three components:[1]

  • The drug causes hepatocellular injury, generally shown by more frequent 3-fold or greater elevations above the upper limits of normal (ULN) of ALT or AST than the (nonhepatotoxic) control agent or placebo.
  • Among subjects showing such aminotransferase (AT) elevations, often with ATs much greater than 3×ULN, some subjects also show elevation of serum total bilirubin (TBL) to >2×ULN, without initial findings of cholestasis (serum alkaline phosphatase (ALP) activity <2×ULN).
  • No other reason can be found to explain the combination of increased AT and serum TBL, such as viral hepatitis A, B, or C, preexisting or acute liver disease, or another drug capable of causing the observed injury.