Liver is a large reddish-brown glandular organ located in the upper right portion of the abdominal cavity behind the rib cage. It secretes bile and functions in metabolism of proteins, carbohydrates and fats. It is known to produce various factors involved in the clotting of the blood & synthesize vitamin A. Liver also breaks down worn-out erythrocytes (RBCs). As most of the chemical compounds, whether taken orally or injected intravenously, are taken to liver, the majority of small-molecule drug metabolism is carried out in the liver by cytochrome P450 which are membrane bound oxidative enzymes which metabolize various endogenous and exogenous molecules.

Action of drugs: Drugs can lead to liver disorders in several ways. Some drugs are directly deleterious to the liver while others are transformed or metabolized by liver into chemicals that can cause liver damage either directly or indirectly.

Dose-dependent toxicity: It occurs when any given drug is taken in excess, the increased concentration of that drug or its metabolite may lead to liver damage. Such drugs are usually harmless if taken within prescribed limits. For example, acetaminophen overdose is known to cause dose-dependent toxicity in liver.

Idiosyncratic toxicity: Drugs that cause idiosyncratic toxicity cause disease in only those few individuals who have inherited specific genes that are associated in some way to the chemical transformation of that particular drug.

Drug allergy: It occurs when a drug or its metabolite acts as an allergen which may initiate hypersensitivity reaction by the body's immune system leading to local inflammation that may damage liver tissues.

Drug induced liver diseases: Various exogenous drugs and endogenous chemicals can cause a wide spectrum of liver injuries. These include, but are not limited to:

Hepatitis: Certain drugs can cause acute and chronic hepatitis (inflammation of liver cells) that can lead to necrosis i.e. cell death. Acute drug-induced hepatitis lasts less than 3 months, while chronic hepatitis lasts longer than 3 months. Some drugs that cause acute and chronic hepatitis include phenytoin, diclophenac, & nitrofurantoin.

Fulminant hepatitis: Rarely, drugs cause acute liver failure or fulminant (sudden & severe) hepatitis. These patients are extremely ill with the symptoms of acute hepatitis.

Cholestasis: It is a condition in which the secretion and/ or flow of bile is reduced. Example- erythromycin, chlorpromazine etc.

Mild elevations in blood liver enzyme levels: Many drugs cause mild elevations in blood levels of liver enzymes, often without any major symptoms. For example, statins & some antidepressants are known to increase levels of liver enzymes in blood.

Necrosis: Blood clotting in the liver veins may cause death of liver cells. For example, Pyrrolizidine alkaloids can cause blood clotting.

Cirrhosis: It is a chronic disease interfering with the normal functioning of the liver due to scarring. Drugs like amiodarone and methyldopa may lead to Cirrhosis.

Diagnosis: Diagnosis of liver disorders is based on a patient's symptoms, which may vary from loss of appetite, nausea, fatigue, itching, dark urine, to jaundice, enlarged liver etc. Laboratory testing may also be used to detect blood liver enzymes levels, bilirubin levels which may suggest abnormal liver behavior. An unusually long blood clotting time may also be an indicative of a potential liver damage.