Silibinin

Silibinin (INN, also known as silybin, trade name Legalon) is the major active constituent of silymarin, the mixture of flavonolignans extracted from blessed milk thistle (Silybum marianum). It is used in the treatment and prevention of liver diseases because of its hepatoprotective (antihepatotoxic) properties. Clinical tests have also shown its ability to protect against certain types of cancer (skin and prostate), probably due to its antioxidant properties.

Chemically modified silibinin, silibinin dihydrogen disuccinate disodium (trade name Legalon SIL) a solution for injection, is used in treatment of severe intoxications with hepatotoxic substances, such as death cap (Amanita phalloides) poisoning.

Pharmacology
Poor water solubility and bioavailability of silymarin led to the development of enhanced formulations. Silipide (trade name Siliphos), a complex of silymarin and phosphatidylcholine (lecithin), is about ten times more bioavailable than silymarin. It has been also reported that silymarin inclusion complex with β-cyclodextrin is much more soluble than silymarin itself. There have also been prepared glycosides of silybin, which show better water solubility and even stronger hepatoprotective effect.

Silymarin, as other flavonoids, has been shown to inhibit P-gp-mediated cellular efflux. The modulation of P-gp- activity may result in altered absorption and bioavailability of drugs that are P-gp- substrates. It has been reported that silymarin inhibit cytochrome P450 enzymes and an interaction with drugs primarily cleared by P450s cannot be excluded.

Toxicity
The acute toxicity of silymarin and silybin were investigated by oral and intravenous route in various animal species. No mortality or any signs of adverse effects were observed after silymarin at oral doses of 20 g/kg in mice and 1 g/kg in dogs. The 50% lethal dose (LD50) after intravenous infusion values are 400 mg/kg in mice, 385 mg/kg in rats and 140 mg/kg in rabbits and dogs. These data demonstrate that the acute toxicity of silymarin is very low. Similarly, its subacute and chronic toxicity are very low; the compound is also devoid of embryotoxic potential.

Complementary and alternative medicine
Silymarin is among the popular complementary medicine for the treatment of cancer. Its use has included treatment of varicose veins, menstrual problems, depression, and low breast milk production. However, the most valuable use of milk thistle-derived silymarin is as a liver supporter to prevent and treat cirrhosis, chronic hepatitis, and gall bladder problems. A recent study suggested that silymarin may help diabetic patients by assisting in blood sugar control.