Drug-Induced Hepatotoxicity

Drug-induced hepatotoxicity, or drug-induced liver injury (DILI), is damage to the liver caused by medications, herbal products, or dietary supplements. Because the liver is the body's principal site of drug metabolism, it is a frequent target of toxic injury, and DILI is a leading reason that drugs are not approved or are withdrawn after marketing.

Definition

Drug-induced hepatotoxicity is liver injury attributable to a drug or its metabolites, ranging from asymptomatic elevations of liver enzymes to acute hepatitis, cholestasis, and acute liver failure, and is classified as intrinsic when dose-dependent and predictable or idiosyncratic when rare and host-dependent.

Scope

This entry covers the concept and classification of DILI, the distinction between intrinsic (dose-dependent) and idiosyncratic injury, the main mechanisms of hepatocellular damage, and the patterns of injury used to describe it. It is a reference-educational overview of how DILI is understood and studied, not clinical guidance on diagnosis or treatment.

Core questions

• What distinguishes intrinsic from idiosyncratic drug-induced liver injury?
• By what mechanisms do drugs and their metabolites injure hepatocytes?
• What patterns of injury (hepatocellular, cholestatic, mixed) are recognised?
• Why are some individuals susceptible to idiosyncratic DILI when most are not?

Key concepts

• Intrinsic (dose-dependent) hepatotoxicity
• Idiosyncratic hepatotoxicity
• Reactive metabolite formation and covalent binding
• Mitochondrial dysfunction
• Hepatocellular, cholestatic, and mixed injury patterns
• Genetic and HLA-associated susceptibility
• Acute liver failure

Mechanisms

Many drugs are converted in the liver to chemically reactive metabolites that deplete protective molecules such as glutathione and bind covalently to cellular proteins, leading to oxidative stress and mitochondrial dysfunction (Tujios & Fontana, 2011). Intrinsic hepatotoxins, of which acetaminophen overdose is the classic example, produce predictable, dose-related injury through these pathways, while idiosyncratic DILI is rare, largely dose-independent, and shaped by host factors. Adaptive immune mechanisms contribute to many idiosyncratic cases, and genetic variation, particularly in human leukocyte antigen (HLA) alleles and drug-metabolizing enzymes, helps explain why only some exposed individuals are affected (Russmann et al., 2010; Uetrecht, 2019). Injury is commonly described by pattern, hepatocellular, cholestatic, or mixed, based on the relative elevation of liver enzymes (Lee, 2003).

Clinical relevance

DILI is a central concern in drug development and pharmacovigilance because it is difficult to predict, can be severe, and is a frequent cause of acute liver failure attributable to medicines. The patterns and mechanisms described here inform how liver injury is recognised and attributed to drugs in surveillance systems. This entry explains how DILI is conceptualised and studied and is not a basis for individual monitoring, diagnosis, or treatment decisions.

Epidemiology

Idiosyncratic DILI is rare on a per-prescription basis but, in aggregate, is among the most common causes of acute liver failure attributed to drugs and a leading reason for drug withdrawals. Acetaminophen is a frequent cause of intrinsic, dose-related hepatotoxicity. Incidence estimates vary with the population, the definitions used, and the surveillance method, and many cases of mild enzyme elevation resolve without progression (Lee, 2003).

History

Recognition that medicines could injure the liver grew through twentieth-century clinical pharmacology and was reinforced by the experience with acetaminophen overdose and by post-marketing hepatotoxicity that prompted regulatory action. Mechanistic and pharmacogenetic research then reframed idiosyncratic DILI around reactive metabolites, mitochondrial injury, and HLA-linked immune susceptibility (Tujios & Fontana, 2011; Russmann et al., 2010).

Debates

How predictable is idiosyncratic DILI before marketing?

Because idiosyncratic injury is rare and host-dependent, it often escapes pre-approval trials; how far reactive-metabolite screening, HLA associations, and other biomarkers can predict risk in advance remains an active question.

Key figures

• William M. Lee
• Robert J. Fontana
• Jack Uetrecht
• Gerd A. Kullak-Ublick

Seminal works

• lee2003
• tujios2011

Frequently asked questions

What is the difference between intrinsic and idiosyncratic drug-induced liver injury?

Intrinsic injury is dose-dependent and predictable, with acetaminophen overdose as the classic example, and tends to affect most people at sufficient exposure. Idiosyncratic injury is rare, largely independent of dose, and depends on host-specific factors such as genetics and immune response.

Why is the liver so often the target of drug toxicity?

The liver is the main site where drugs are metabolised, so it is exposed to high concentrations of drugs and to the reactive metabolites generated during their breakdown, which can injure liver cells.