In the world of pharmacovigilance, few adverse events command as much respect and caution as Drug-Induced Liver Injury (DILI). It is a leading cause of acute liver failure in the Western world and remains the single most frequent safety-related reason for the withdrawal of drugs from the market.

Whether you are in clinical development or post-marketing surveillance, understanding the mechanisms, detection methods, and regulatory landscape of DILI is essential.

What is DILI?

DILI is an injury to the liver caused by a medication, herb, or dietary supplement. While some drugs cause liver injury in a predictable, dose-dependent manner (known as intrinsic DILI, like Acetaminophen toxicity), the majority of cases in clinical practice are idiosyncratic.

Idiosyncratic DILI is unpredictable, largely independent of dose, and driven by a complex interplay of host factors (genetics, immune response) and environmental conditions. More recently, a third category called “Indirect DILI” has been proposed, arising from the biological action of the drug itself, such as immune checkpoint inhibitors causing immune-mediated hepatitis.

The “Golden Rule” of Liver Safety: Hy’s Law

If you work in drug safety, you have likely heard of Hy’s Law. Named after Dr. Hyman Zimmerman, this observation states that drug-induced hepatocellular injury accompanied by jaundice (without biliary obstruction) is a serious lesion with a mortality rate of 10–50%.

Regulatory agencies like the FDA use specific criteria to identify potential Hy’s Law cases in clinical trials to predict severe hepatotoxicity:

1. Hepatocellular Injury: ALT or AST > 3x Upper Limit of Normal (ULN).
2. Liver Function Impairment: Total Bilirubin (TBL) > 2x ULN.
3. Absence of Obstruction: Alkaline Phosphatase (ALP) < 2x ULN.
4. No Other Cause: Exclusion of viral hepatitis, alcohol, or other pre-existing diseases.

Finding even one or two Hy’s Law cases in a clinical trial database is considered ominous and highly predictive of severe DILI in a larger post-marketing population.

The Rise and Fall of Esmya®: A Case Study in DILI

The story of Esmya® (ulipristal acetate) provides a stark lesson in how DILI signals can alter the lifecycle of a promising drug.

• The Promise: Esmya was approved in the EU in 2012 for the pre-operative treatment of uterine fibroids. It demonstrated efficacy in reducing bleeding and fibroid size. Analysts forecasted it to be a blockbuster with sales potential over $800 million.
• The Signal: By late 2017, reports emerged of serious liver injury, including cases requiring liver transplantation.
• Regulatory Action: * EMA (2017-2018): Initiated a review triggered by these reports. Temporary measures were introduced, including monitoring liver function monthly and stopping treatment if transaminases rose > 2x ULN.
  • FDA (2018): Rejected the New Drug Application (NDA) for ulipristal acetate for fibroids, citing safety concerns.
  • Withdrawal (2020-2021): Following further cases of liver failure, the PRAC recommended revoking marketing authorization. The drug was eventually restricted or withdrawn in several markets, including the EU and Canada.

This case underscores that short-term clinical trials may not always capture rare idiosyncratic events, which often only surface when the drug is exposed to a larger, more diverse population.

Tools for the PV Professional

Detecting DILI requires a rigorous exclusion of alternative causes (such as Hepatitis A/B/C/E, autoimmune hepatitis, or alcohol use). Several tools aid in this assessment:

1. RUCAM Scale

The Roussel Uclaf Causality Assessment Method (RUCAM) is the most commonly used tool for establishing causality in DILI cases. It scores domains such as time to onset, risk factors, and concomitant drugs to determine if a relationship is “excluded,” “possible,” “probable,” or “highly probable”.

2. LiverTox®

A collaborative database by the NIDDK and NLM, LiverTox provides up-to-date clinical information on liver injury attributable to prescription drugs and herbal supplements.

3. DILIrank

A massive dataset curated by the FDA that ranks over 1,000 drugs based on their potential for causing liver injury (vRank), classified into “Most-DILI-Concern,” “Less-DILI-Concern,” and “No-DILI-Concern”.

Future Directions: Beyond ALT

Current standard biomarkers (ALT, AST, ALP) are indicators of damage, not necessarily function or prediction. The industry is moving toward new exploratory biomarkers such as:

• Glutamate Dehydrogenase (GLDH): A marker for mitochondrial injury.
• MicroRNA 122 (miR122): An early, specific marker of hepatocellular necrosis.
• Cytokeratin 18 (CK18): Indicates hepatocyte necrosis and apoptosis.

While these are not yet standard in all clinical practice, they represent the future of safer drug development and more precise signal detection.

Conclusion

DILI remains a complex diagnostic puzzle. It requires pharmacovigilance professionals to maintain a high index of suspicion, rigorously apply causality assessment tools like RUCAM, and closely monitor regulatory updates. As the Esmya case demonstrates, vigilance does not end at approval; it is a continuous commitment to patient safety.