Anti-herpes virus activity of silibinin, the primary active component of Silybum marianum

Silibinin (silybin A and silybin B), the primary active component of Silybum marianum has antiviral activity against herpes simplex virus, type 2 (HSV-2). The fifty percent cytotoxic dose (CD50) of silibinin was 378 μg/ml. By plaque reduction assay silibinin had a weak antiviral effect against HSV-2 with a fifty percent inhibitory concentration (IC50) of 100 μg/ml and therapeutic index of 3.8. As a virucide, silibinin was more potent with an IC50 of 5 μg/ml and therapeutic index of 76. Further investigations of the mechanisms of action of silibinin against herpes simplex viruses and subsequent silibinin monotherapy or combination therapy with other flavonoids as a topical treatment for genital herpes are warranted.