Show notes
Episode one of the Drug-Induced Liver Injury and Acute Liver Failure chapter builds drug injury from a single mechanism: cytochrome oxidation makes a reactive intermediate, phase-two conjugation quenches it or fails, and injury appears where phase one outpaces phase two. That frame makes the offender lists predictable, the histology readable, and the severity rules non-arbitrary. Hy's Law converts biochemistry into a triage decision, R value predicts trajectory, and histology patterns map backward to drug classes. Acetaminophen is the prototype that runs the whole sequence at speed, with the Rumack-Matthew nomogram, N-acetylcysteine, and time-to-treatment mortality all board-tested cold.
Topics covered
Drug injury as the diagnosis for any new abnormal liver tests
Intrinsic versus idiosyncratic versus indirect hepatotoxicity
Epidemiology and environmental plus genetic risk factors
Herbal and dietary supplement injury
Metabolic activation and the phase-one, phase-two two-step
Agent-specific patterns from isoniazid to amiodarone
Hy's Law, R value, and causality assessment
Histology patterns mapped to drug classes
Acetaminophen toxicity, the nomogram, and N-acetylcysteine
Key decisions
Hy's Law is met when transaminases exceed three times normal, total bilirubin exceeds two times normal, alkaline phosphatase is under two times normal, and no other cause explains it, at which point mortality is about ten percent and the drug is stopped with transplant-center awareness.
The R value classifies pattern, hepatocellular over five, cholestatic under two, mixed between, with hepatocellular injury more likely to evolve to acute failure and cholestatic or mixed more likely to become chronic.
Acetaminophen toxicity occurs when NAPQI production exceeds glutathione capacity, so a chronic alcohol user with CYP2E1 induction and glutathione depletion can develop fulminant injury on therapeutic-range dosing without ever taking an overdose.
An acute single ingestion of seven and a half grams or more in an adult, or over a hundred fifty milligrams per kilogram in a child, puts the patient in the toxic window.
The Rumack-Matthew treatment line runs from a hundred fifty micrograms per milliliter at four hours down to about five at twenty-four hours, and a level above that line within the four-to-twenty-four-hour window indicates N-acetylcysteine.
Intravenous N-acetylcysteine is dosed as a hundred fifty milligrams per kilogram over sixty minutes, then fifty over four hours, then a hundred over sixteen hours, totaling three hundred over twenty-one hours, and started the moment the diagnosis is suspected because mortality roughly doubles with each block of delay.
Drug-induced autoimmune-like hepatitis from nitrofurantoin, minocycline, hydralazine, or methyldopa usually remits when the drug stops and does not need long-term immunosuppression, unlike idiopathic autoimmune hepatitis which flares on steroid taper.
For the full chapter with MCQs, tables, and primary-guideline references, visit www.boardpearls.com.
Questions or feedback: [email protected].
(00:00) - Introduction and the mechanistic frame
(01:17) - Intrinsic, idiosyncratic, and indirect injury
(02:18) - Epidemiology and risk factors
(04:46) - Herbal and dietary supplements
(05:56) - Metabolic activation: the hepatic two-step
(08:21) - Agent-specific patterns
(11:21) - Hy's Law, R value, and causality
(14:34) - Histology patterns by drug class
(20:11) - Acetaminophen: nomogram and antidote