Hepatotoxicity | |
---|---|
Other names | see below list |
Drug-induced hepatitis with granulomata. Other causes were excluded with extensive investigations. Liver biopsy. H&E stain. | |
Specialty | Gastroenterology, Toxicology |
Complications | Cirrhosis, liver failure |
Synonyms |
---|
Drug-induced liver injury (DILI) Contents
|
Hepatotoxicity (from hepatic toxicity) implies chemical-driven liver damage. Drug-induced liver injury (DILI) is a cause of acute and chronic liver disease caused specifically by medications and the most common reason for a drug to be withdrawn from the market after approval.
The liver plays a central role in transforming and clearing chemicals and is susceptible to the toxicity from these agents. Certain medicinal agents, when taken in overdoses (e.g. acetaminophen, paracetamol) and sometimes even when introduced within therapeutic ranges (e.g. halothane), may injure the organ. Other chemical agents, such as those used in laboratories and industries, natural chemicals (e.g., alpha-amanitin), and herbal remedies (two prominent examples being kava, though the causal mechanism is unknown, and comfrey, through pyrrolizidine alkaloid content) can also induce hepatotoxicity. Chemicals that cause liver injury are called hepatotoxins.
More than 900 drugs have been implicated in causing liver injury [1] (see LiverTox, external link, below) and it is the most common reason for a drug to be withdrawn from the market. Hepatotoxicity and drug-induced liver injury also account for a substantial number of compound failures, highlighting the need for toxicity prediction models (e.g. DTI), [2] and drug screening assays, such as stem cell-derived hepatocyte-like cells, that are capable of detecting toxicity early in the drug development process. [3] Chemicals often cause subclinical injury to the liver, which manifests only as abnormal liver enzyme tests.
Drug-induced liver injury is responsible for 5% of all hospital admissions and 50% of all acute liver failures. [4] [5]
Adverse drug reactions are classified as type A (intrinsic or pharmacological) or type B (idiosyncratic). [6] Type A drug reaction accounts for 80% of all toxicities. [7]
Drugs or toxins that have a pharmacological (type A) hepatotoxicity are those that have predictable dose-response curves (higher concentrations cause more liver damage) and well characterized mechanisms of toxicity, such as directly damaging liver tissue or blocking a metabolic process. As in the case of paracetamol overdose, this type of injury occurs shortly after some threshold for toxicity is reached. Carbon tetrachloride is commonly used to induce acute type A liver injury in animal models.
Idiosyncratic (type B) injury occurs without warning, when agents cause non-predictable hepatotoxicity in susceptible individuals, which is not related to dose and has a variable latency period. [8] This type of injury does not have a clear dose-response nor temporal relationship, and most often does not have predictive models. Idiosyncratic hepatotoxicity has led to the withdrawal of several drugs from market even after rigorous clinical testing as part of the FDA approval process; Troglitazone (Rezulin) [2] [9] and trovafloxacin (Trovan) are two prime examples of idiosyncratic hepatotoxins pulled from market.
The herb kava has caused a number of cases of idiosyncratic liver injury, ranging everywhere from asymptomatic to fatal.
Oral use of the antifungal ketoconazole has been associated with hepatic toxicity, including some fatalities; [10] however, such effects appear to be limited to doses taken over a period longer than 7 days. [11]
Paracetamol also known as acetaminophen, and by the brand names of Tylenol and Panadol, is usually well-tolerated in prescribed dose, but overdose is the most common cause of drug-induced liver disease and acute liver failure worldwide. [12] Damage to the liver is not due to the drug itself but to a toxic metabolite (N-acetyl-p-benzoquinone imine (NAPQI)) produced by cytochrome P-450 enzymes in the liver. [13] In normal circumstances, this metabolite is detoxified by conjugating with glutathione in phase 2 reaction. In an overdose, a large amount of NAPQI is generated, which overwhelms the detoxification process and leads to liver cell damage. Nitric oxide also plays a role in inducing toxicity. [14] The risk of liver injury is influenced by several factors including the dose ingested, concurrent alcohol or other drug intake, interval between ingestion and antidote, etc. The dose toxic to the liver is quite variable from person to person and is often thought to be lower in chronic alcoholics. [15] [16] Measurement of blood level is important in assessing prognosis, higher levels predicting a worse prognosis. Administration of Acetylcysteine, a precursor of glutathione, can limit the severity of the liver damage by capturing the toxic NAPQI. Those that develop acute liver failure can still recover spontaneously, but may require transplantation if poor prognostic signs such as encephalopathy or coagulopathy is present (see King's College Criteria). [17]
Although individual analgesics rarely induce liver damage due to their widespread use, NSAIDs have emerged as a major group of drugs exhibiting hepatotoxicity. Both dose-dependent and idiosyncratic reactions have been documented. [18] Aspirin and phenylbutazone are associated with intrinsic hepatotoxicity; idiosyncratic reaction has been associated with ibuprofen, sulindac, phenylbutazone, piroxicam, diclofenac and indomethacin.
Glucocorticoids are so named due to their effect on the carbohydrate mechanism. They promote glycogen storage in the liver. An enlarged liver is a rare side-effect of long-term steroid use in children. [19] The classical effect of prolonged use both in adult and paediatric population is steatosis. [20]
Isoniazide (INH) is one of the most commonly used drugs for tuberculosis; it is associated with mild elevation of liver enzymes in up to 20% of patients and severe hepatotoxicity in 1-2% of patients. [21]
There are also cases where other hydrazine derivative drugs, such as the MAOI antidepressant iproniazid, are associated with liver damage. [22] [23] Phenelzine has been associated with abnormal liver tests. [24] Toxic effects can develop from antibiotics. [25]
Examples include alpha-Amanitin containing mushrooms, kava, and aflatoxin producing molds. Pyrrolizidine alkaloids, which occur in some plants, can be toxic. [26] [27] Green tea extract is a growing cause of liver failure due to its inclusion in more products. [28] [29] [30]
Examples include: Ackee fruit, Bajiaolian, Camphor, Copaltra, Cycasin, Garcinia, [31] Kava leaves, pyrrolizidine alkaloids, Horse chestnut leaves, Valerian, Comfrey. [32] [33] Chinese herbal remedies: Jin Bu Huan, Ephedra, Shou Wu Pian, Bai Xian Pi. [34] [35]
Examples include arsenic, carbon tetrachloride, and vinyl chloride. [36]
Factors influencing drug-induced hepatotoxicity [12] |
---|
|
Drugs continue to be taken off the market due to late discovery of hepatotoxicity. Due to its unique metabolism and close relationship with the gastrointestinal tract, the liver is susceptible to injury from drugs and other substances. 75% of blood coming to the liver arrives directly from gastrointestinal organs and the spleen via portal veins that bring drugs and xenobiotics in near-undiluted form. Several mechanisms are responsible for either inducing hepatic injury or worsening the damage process.
Many chemicals damage mitochondria, an intracellular organelle that produces energy. Its dysfunction releases excessive amount of oxidants that, in turn, injure hepatic cells. Activation of some enzymes in the cytochrome P-450 system such as CYP2E1 also lead to oxidative stress. [37] Injury to hepatocyte and bile duct cells lead to accumulation of bile acid inside the liver. This promotes further liver damage. [38] Non-parenchymal cells such as Kupffer cells, collagen-producing stellate cells, and leukocytes (i.e. neutrophil and monocyte) also have a role in the mechanism.
The human body subjects most, but not all, compounds to various chemical processes (i.e. metabolism) to make them suitable for elimination. This involves chemical transformations to (a) reduce fat solubility and (b) to change biological activity. Although almost all tissues in the body have some ability to metabolize chemicals, smooth endoplasmic reticulum in the liver is the principal "metabolic clearing house" for both endogenous chemicals (e.g., cholesterol, steroid hormones, fatty acids, proteins) and exogenous substances (e.g., drugs, alcohol). [39] The central role played by liver in the clearance and transformation of chemicals makes it susceptible to drug-induced injury.
Drug metabolism is usually divided into two phases: phase 1 and phase 2. Phase 1 reaction is generally speaking to prepare a drug for phase 2. However, many compounds can be metabolized by phase 2 directly or be excreted without any phase 2 reactions occurring. Phase 1 reaction involves oxidation, reduction, hydrolysis, hydration and many other rare chemical reactions. These processes tend to increase water solubility of the drug and can generate metabolites that are more chemically active and/or potentially toxic. Most of phase 2 reactions take place in cytosol and involve conjugation with endogenous compounds via transferase enzymes. Phase 1 are typically more suitable for elimination.
A group of enzymes located in the endoplasmic reticulum, known as cytochrome P-450, is the most important family of metabolizing enzymes in the liver. Cytochrome P-450 is not a single enzyme, but rather consists of a closely related family of 50 isoforms; six of them metabolize 90% of drugs. [40] [41] There is a tremendous diversity of individual P-450 gene products, and this heterogeneity allows the liver to perform oxidation on a vast array of chemicals (including most drugs) in phase 1. Three important characteristics of the P-450 system have roles in drug-induced toxicity:
Each of the P-450 proteins is unique and accounts (to some extent) for the variation in drug metabolism between individuals. Genetic variations (polymorphism) in P-450 metabolism should be considered when patients exhibit unusual sensitivity or resistance to drug effects at normal doses. Such polymorphism is also responsible for variable drug response among patients of differing ethnic backgrounds.
Potent inducers | Potent inhibitors | Substrates |
---|---|---|
Rifampicin, Carbamazepine, Phenobarbital, Phenytoin, St John's wort, | Amiodarone, Cimetidine, Ciprofloxacin, Fluconazole, Fluoxetine, Erythromycin, Isoniazid, Diltiazem | Caffeine, Clozapine, Omeprazole, Losartan, Theophylline |
Many substances can influence the P-450 enzyme mechanism. Drugs interact with the enzyme family in several ways. [44] Drugs that modify cytochrome P-450 enzyme are referred to as either inhibitors or inducers. Enzyme inhibitors block the metabolic activity of one or several P-450 enzymes. This effect usually occurs immediately. On the other hand, inducers increase P-450 activity by increasing enzyme production, or, in the case of CYP2E1, preventing degradation in the proteasome. There is usually a delay before enzyme activity increases. [41]
Some drugs may share the same P-450 specificity and thus competitively block their biotransformation. This may lead to accumulation of drugs metabolized by the enzyme. This type of drug interaction may also reduce the rate of generation of toxic metabolites.
Type of injury: | Hepatocellular | Cholestatic | Mixed |
---|---|---|---|
ALT | ≥ Twofold rise | Normal | ≥ Twofold rise |
ALP | Normal | ≥ Twofold rise | ≥ Twofold rise |
ALT: ALP ratio | High, ≥5 | Low, ≤2 | 2–5 |
Examples [45] | Acetaminophen Allopurinol Amiodarone HAART NSAID | Anabolic steroid Chlorpromazine Clopidogrel Erythromycin Hormonal contraception | Amitriptyline, Enalapril Carbamazepine Sulfonamide Phenytoin |
Chemicals produce a wide variety of clinical and pathological hepatic injury. Biochemical markers (e.g. alanine transferase, alkaline phosphatase and bilirubin) are often used to indicate liver damage. Liver injury is defined as a rise in either (a) ALT level more than three times of upper limit of normal (ULN), (b) ALP level more than twice ULN, or (c) total bilirubin level more than twice ULN when associated with increased ALT or ALP. [45] [46] Liver damage is further characterized into hepatocellular (predominantly initial Alanine transferase elevation) and cholestatic (initial alkaline phosphatase rise) types. However they are not mutually exclusive and mixed types of injuries are often encountered.
Specific histo-pathological patterns of liver injury from drug-induced damage are discussed below.
This is the most common type of drug-induced liver cell necrosis where the injury is largely confined to a particular zone of the liver lobule. It may manifest as a very high level of ALT and severe disturbance of liver function leading to acute liver failure.
In this pattern, hepatocellular necrosis is associated with infiltration of inflammatory cells. There can be three types of drug-induced hepatitis. (A) viral hepatitis is the most common, where histological features are similar to acute viral hepatitis. (B) in focal or non-specific hepatitis, scattered foci of cell necrosis may accompany lymphocytic infiltration. (C) chronic hepatitis is very similar to autoimmune hepatitis clinically, serologically, and histologically.
Liver injury leads to impairment of bile flow and cases are predominated by itching and jaundice. Histology may show inflammation (cholestatic hepatitis) or it can be bland (without any parenchymal inflammation). On rare occasions, it can produce features similar to primary biliary cirrhosis due to progressive destruction of small bile ducts (vanishing duct syndrome).
Hepatotoxicity may manifest as triglyceride accumulation, which leads to either small-droplet (microvesicular) or large-droplet (macrovesicular) fatty liver. There is a separate type of steatosis by which phospholipid accumulation leads to a pattern similar to the diseases with inherited phospholipid metabolism defects (e.g., Tay–Sachs disease)
Drug-induced hepatic granulomas are usually associated with granulomas in other tissues and patients typically have features of systemic vasculitis and hypersensitivity. More than 50 drugs have been implicated.
These result from injury to the vascular endothelium.
Neoplasms have been described with prolonged exposure to some medications or toxins. Hepatocellular carcinoma, angiosarcoma, and liver adenomas are the ones usually reported.
This remains a challenge in clinical practice due to a lack of reliable markers. [47] Many other conditions lead to similar clinical as well as pathological pictures. To diagnose hepatotoxicity, a causal relationship between the use of the toxin or drug and subsequent liver damage has to be established, but might be difficult, especially when idiosyncratic reaction is suspected. [48] Simultaneous use of multiple drugs may add to the complexity. As in acetaminophen toxicity, well established, dose-dependent, pharmacological hepatotoxicity is easier to spot. Several clinical scales such as CIOMS/RUCAM scale and Maria and Victorino criteria have been proposed to establish causal relationship between offending drug and liver damage. CIOMS/RUCAM scale involves a scoring system that categorizes the suspicion into "definite or highly probable" (score > 8), "probable" (score 6–8), "possible" (score 3–5), "unlikely" (score 1–2) and "excluded" (score ≤ 0). In clinical practice, physicians put more emphasis on the presence or absence of similarity between the biochemical profile of the patient and known biochemical profile of the suspected toxicity (e.g., cholestatic damage in amoxycillin-clauvonic acid ). [47]
In most cases, liver function will return to normal if the offending drug is stopped early. Additionally, the patient may require supportive treatment. In acetaminophen toxicity, however, the initial insult can be fatal. Fulminant hepatic failure from drug-induced hepatotoxicity may require liver transplantation. In the past, glucocorticoids in allergic features and ursodeoxycholic acid in cholestatic cases had been used, but there is no good evidence to support their effectiveness.[ citation needed ]
An elevation in serum bilirubin level of more than 2 times ULN with associated transaminase rise is an ominous sign. This indicates severe hepatotoxicity and is likely to lead to mortality in 10% to 15% of patients, especially if the offending drug is not stopped (Hy's Law). [49] [50] This is because it requires significant damage to the liver to impair bilirubin excretion, hence minor impairment (in the absence of biliary obstruction or Gilbert syndrome) would not lead to jaundice. Other poor predictors of outcome are old age, female sex, high AST. [51] [52]
The following therapeutic drugs were withdrawn from the market primarily because of hepatotoxicity: Troglitazone, bromfenac, trovafloxacin, ebrotidine, nimesulide, nefazodone, ximelagatran and pemoline. [47] [53] [54]
Paracetamol (acetaminophen) is a non-opioid analgesic and antipyretic agent used to treat fever and mild to moderate pain. It is a widely used over-the-counter medication. Common brand names include Tylenol and Panadol.
Alanine transaminase (ALT), also known as alanine aminotransferase, formerly serum glutamate-pyruvate transaminase (GPT) or serum glutamic-pyruvic transaminase (SGPT), is a transaminase enzyme that was first characterized in the mid-1950s by Arthur Karmen and colleagues. ALT is found in plasma and in various body tissues but is most common in the liver. It catalyzes the two parts of the alanine cycle. Serum ALT level, serum AST level, and their ratio are routinely measured clinically as biomarkers for liver health.
Alcoholic liver disease (ALD), also called alcohol-related liver disease (ARLD), is a term that encompasses the liver manifestations of alcohol overconsumption, including fatty liver, alcoholic hepatitis, and chronic hepatitis with liver fibrosis or cirrhosis.
Isoniazid, also known as isonicotinic acid hydrazide (INH), is an antibiotic used for the treatment of tuberculosis. For active tuberculosis, it is often used together with rifampicin, pyrazinamide, and either streptomycin or ethambutol. For latent tuberculosis, it is often used alone. It may also be used for atypical types of mycobacteria, such as M. avium, M. kansasii, and M. xenopi. It is usually taken by mouth, but may be used by injection into muscle.
Thromboxane is a member of the family of lipids known as eicosanoids. The two major thromboxanes are thromboxane A2 and thromboxane B2. The distinguishing feature of thromboxanes is a 6-membered ether-containing ring.
Cytochrome P450 2E1 is a member of the cytochrome P450 mixed-function oxidase system, which is involved in the metabolism of xenobiotics in the body. This class of enzymes is divided up into a number of subcategories, including CYP1, CYP2, and CYP3, which as a group are largely responsible for the breakdown of foreign compounds in mammals.
Zafirlukast is an orally administered leukotriene receptor antagonist (LTRA) used for the chronic treatment of asthma. While zafirlukast is generally well tolerated, headaches and stomach upset often occur. Some rare side effects can occur, which can be life-threatening, such as liver failure. eosinophilic granulomatosis with polyangiitis has been associated with zafirlukast, but the relationship isn't thought to be causative. Overdoses of zafirlukast tend to be self-limiting.
Toxication, toxification or toxicity exaltation is the conversion of a chemical compound into a more toxic form in living organisms or in substrates such as soil or water. The conversion can be caused by enzymatic metabolism in the organisms, as well as by abiotic chemical reactions. While the parent drug is usually less active, both the parent drug and its metabolite can be chemically active and cause toxicity, leading to mutagenesis, teratogenesis, and carcinogenesis. Different classes of enzymes, such as P450 monooxygenases, epoxide hydrolase, or acetyltransferases can catalyze the process in the cell, mostly in the liver.
Acute liver failure is the appearance of severe complications rapidly after the first signs of liver disease, and indicates that the liver has sustained severe damage. The complications are hepatic encephalopathy and impaired protein synthesis. The 1993 classification defines hyperacute as within 1 week, acute as 8–28 days, and subacute as 4–12 weeks; both the speed with which the disease develops and the underlying cause strongly affect outcomes.
Tienilic acid or ticrynafen (USAN) is a loop diuretic drug with uric acid-lowering (uricosuric) action, formerly marketed for the treatment of hypertension. It was approved by FDA on May 2, 1979, and withdrawn in 1982, after case reports in the United States indicated a link between the use of ticrynafen and hepatitis.
Iproniazid is a non-selective, irreversible monoamine oxidase inhibitor (MAOI) of the hydrazine class. It is a xenobiotic that was originally designed to treat tuberculosis, but was later most prominently used as an antidepressant drug. However, it was withdrawn from the market because of its hepatotoxicity. The medical use of iproniazid was discontinued in most of the world in the 1960s, but remained in use in France until its discontinuation in 2015.
A hepatotoxin is a toxic chemical substance that damages the liver.
NAPQI, also known as NAPBQI or N-acetyl-p-benzoquinone imine, is a toxic byproduct produced during the xenobiotic metabolism of the analgesic paracetamol (acetaminophen). It is normally produced only in small amounts, and then almost immediately detoxified in the liver.
The King's College Criteria or the King's College Hospital criteria were devised in 1989 to determine if there were any early indices of poor prognosis in patients with acute liver failure. Acute liver failure is defined as the onset of encephalopathy or coagulopathy within 26 weeks of a patient diagnosed with liver disease. Patients with hepatitis B acquired at birth, Wilson's disease and autoimmune hepatitis are included if their disease was identified within the past 26 weeks. These patients are very ill, and have a very high risk of dying of their illness without adequate treatment which may include liver transplantation. It is important that physicians find ways of identifying patients with acute liver failure early in their course who will do poorly, and may require liver transplantation. The King's College Criteria have consistently shown excellent operating characteristics for determining prognosis in these patients. As liver transplantation becomes a more accessible option for patients with acute liver failure, the King's College Criteria serve a role in determining which patients may require transplantation.
Hydrocodone/paracetamol is the combination of the pain medications hydrocodone and paracetamol (acetaminophen). It is used to treat moderate to severe pain. It is taken by mouth. Recreational use is common in the United States.
Benoxaprofen, also known as benoxaphen, is a chemical compound with the formula C16H12ClNO3. It is a non-steroidal anti-inflammatory drug (NSAID) of the arylpropionic acid class, and was marketed under the brand name Opren in the United Kingdom and Europe by Eli Lilly and Company (commonly referred to as Lilly), and as Oraflex in the United States of America (USA). Lilly suspended sales of Oraflex in 1982 after reports from the British government and the United States Food and Drug Administration (US FDA) of adverse effects and deaths linked to the drug.
The CIOMS/RUCAM scale is a tool to predict whether liver damage can be attributed to a particular medication.
Paracetamol poisoning, also known as acetaminophen poisoning, is caused by excessive use of the medication paracetamol (acetaminophen). Most people have few or non-specific symptoms in the first 24 hours following overdose. These symptoms include feeling tired, abdominal pain, or nausea. This is typically followed by absence of symptoms for a couple of days, after which yellowish skin, blood clotting problems, and confusion occurs as a result of liver failure. Additional complications may include kidney failure, pancreatitis, low blood sugar, and lactic acidosis. If death does not occur, people tend to recover fully over a couple of weeks. Without treatment, death from toxicity occurs 4 to 18 days later.
Liver regeneration is the process by which the liver is able to replace damaged or lost liver tissue. The liver is the only visceral organ with the capacity to regenerate. The liver can regenerate after partial hepatectomy or injury due to hepatotoxic agents such as certain medications, toxins, or chemicals. Only 51% of the original liver mass is required for the organ to regenerate back to full size. The phenomenon of liver regeneration is seen in all vertebrates, from humans to fish. The liver manages to restore any lost mass and adjust its size to that of the organism, while at the same time providing full support for body homeostasis during the entire regenerative process. The process of regeneration in mammals is mainly compensatory growth or hyperplasia because while the lost mass of the liver is replaced, it does not regain its original shape. During compensatory hyperplasia, the remaining liver tissue becomes larger so that the organ can continue to function. In lower species such as fish, the liver can regain both its original size and mass.
HepaRG cell line is a human hepatic in vitro line used in liver biology research and for assessing liver pathology, hepatotoxicity, and drug-induced injury. The HepaRG model is considered a surrogate for Primary Human Hepatocytes, which are the most pertinent model to reproduce the human liver functioning as they express 99% of the same genes.