Drug-drug interactions of silymarin on the perspective of pharmacokinetics

Silymarin, which is extracted from the milk thistle (Silybum marianum), has been used for centuries for treating hepatic disorders and its hepatoprotective effects have been known for hundreds of years. Silymarin is a mixture of polyphenoic flavonoids, which include silibinin (silybin A and silybin B), isosilyin A and B, silychristin A and B, silydianin and other phenol compounds. The pharmacokinetics of silibinin shows fast absorption and elimination. Silymarin undergoes phase I and phase II metabolism, especially phase II conjugation reactions, it undergoes multiple conjugation reactions, and is primarily excreted into bile and urine. Silymarin has a good safety profile, but little is known regarding its potential for drug interaction. Silymarin has limited effect on the pharmacokinetics of several drugs in vivo; despite silymarin decreasing the activity of cytochrome P-450 (CYPs) enzymes, UDP-glucuronosyltransferase (UGT) enzyme, and reducing P-glycoprotein (P-gp) transport. Health-care practitioners should caution patients against co-administration of silymarin and pharmaceutical drugs.