There have been rare cases of Orlistat use leading to elevated transaminase, elevated alkaline phosphatase, and severe hepatitis. There have also been cases of liver failure, some of which required liver transplant surgery or led to death. Orlistat has also had rare reports of allergic reactions, mostly including itchiness, rashes, hives, neurovascular edema, bronchospasm and allergic reactions, as well as very rare reports of herpes. Monitoring of sales also found reports of pancreatitis.
Mechanism of Action
Orlistat is a type of lipase inhibiting weight loss drug and is a hydrated derivative of lipostatin. Orlistat effectively and selectively inhibits stomach lipase and pancreatic lipase, while having no impact on other digestive enzymes (such as amylase, trypsin and chymotrypsin) and on phospholipase, nor does it affect the absorption of carbohydrates, protein and phospholipids. This drug is not absorbed though the gastrointestinal tract and has a reversible inhibiting effect on lipase. Orlistat deactivates enzymes by covalent binding to the serine residue on the active sites of stomach and pancreatic lipase. This prevents the fat in food from being broken down into free fatty acids and diacylglycerol, so it cannot be absorbed, lowering caloric intake and therefore controlling body weight. This drug does not need to be absorbed by the entire body to take effect. Orlistat’s pharmacological activity is dose dependent: a treatment dosage of Orlistat (120mg/d, tid, taken with meals), combined with a low-calorie diet, can reduce up to 30% of fat absorption. In a study comparing normal and obese volunteers, Orlistat was basically not absorbed by the body at all and had a very low blood concentration. After a single oral dosage (the largest being 800mg), the blood concentration of Orlistat in the following 8 hours was <5 ng/ml. Typically, a treatment dosage of Orlistat is only minimally absorbed by the body and will not accumulate in a short treatment period. In an in vitro experiment, Orlistat’s binding rate with other serum proteins exceeded 99% (bound proteins were mainly lipoproteins and albumin), and its binding rate with red blood cells was very low.
Indications and Usage
Orlistat is an internationally recognized new form of weight loss drug. Its commercial name is Sainike and first went on sale in New Zealand in 1998. Orlistat is a long-term and highly effective specific gastrointestinal lipase inhibitor, and it is insoluble in water, soluble in chloroform, and easily soluble in ethanol.
Orlistat can be used clinically to treat obesity. Usually, a dose of 120mg is taken three times a day within one hour of a meal. Weight loss begins to occur after two weeks of usage. It can be used continuously for 6-12 months, and its effects will cease to increase after daily dosage exceeds 400mg. This drug is suitable to be used in combination with a low-calorie diet by obese and overweight individuals, and it can also be used as long-term treatment for patients who have faced weight-related risk factors. Orlistat has a long-term weight-control effect that reduces and maintains weight and prevents against rebounding. Using Orlistat can lower the occurrences of weight-related risk factors and diseases, including hypercholesterolemia, type-2 diabetes, impaired glucose tolerance, hyperinsulinemia, and hypertension, and it can reduce the fat content in organs. Orlistat also adjusts blood lipid levels: it can decrease serum triglycerides (TG) and low density lipoprotein cholesterol (LDL-C), and it can increase the ratio of high density lipoproteins to low density lipoproteins in obese patients.
An antiobesity agent. A pancreatic lipase inhibitor. Antiobesity agent.
Minimal absorption when ingested orally, can be metabolized and deactivated in the intestinal tract, metabolizing area is the stomach wall, clearing half-life is about 14-19 hours. A study of obese patients showed that the essentially unabsorbed Orlistat produced two main metabolites in blood: M1(4 lactone ring hydrolysate) and M3 (M1 adhered to an N-leucine cleavage product) compose 42% of total blood concentration. M1 and M3 have extremely weak inhibiting effects on lipase and can both be excreted through bile. About 97% of the drug is excreted through feces, 83% of which is excreted in its original form. The cumulative renal output of Orlistat and its metabolites is lower than 2%, and the complete excretion of the drug (through feces and urine) requires 3-5 days.
Warnings and Precautions
Orlistat has led to rare cases of acute hepatocellular necrosis and acute liver failure, some of which required liver transplants or led to death. Thus, prescribing physicians must inform patients to immediately cease use of Orlistat and other suspicious drugs and seek inspection for liver functions if any symptoms or signs of liver function abnormalities occur (such as reduced appetite, itchiness, jaundice, dark urine, light feces, or pain in the upper right quadrant).
Tetrahydrolipstatin (orlistat) is a semi-synthetic derivative of lipstatin, a metabolite isolated from Streptomyces toxytricini. Tetrahydrolipstatin acts as a potent, irreversible inhibitor of pancreatic lipase. In vivo, it blocks the absorption of triglycerides while allowing fatty acid absorption. Tetrahydrolipstatin is widely used for the treatment of obesity.
Orlistat is an antiobesity agent. Orlistat is an pancreatic lipase inhibitor.
May reduce absorption of vitamin A, D and E; take supplements when using this drug. Any preparations containing vitamin A, D or E (such as compound vitamin preparations), should be taken 2 hours after this drug or before bed.
Type-2 diabetes patients may need to decrease dosage of antidiabetic drugs (such as sulfonylurea).
Combined use with cyclosporine may lower the blood concentration of the latter drug.
Combined use with amiodarone may reduce absorption of the latter drug, thus decreasing its curative effects.
Hypolipemic pancreatic, gastric and carboxylester lipase inhibitor. Exhibits no activity at phospholipase A 2 , liver esterase, trypsin and chymotrypsin. Inhibits the thioesterase domain of fatty acid synthase, leading to cell cycle arrest at the G 1 /S boundary in vitro . Prevents the absorption of approximately one third of fat from food and exhibits progastrokinetic, antiobesity and antihypercholesterolemic activity in vivo .