GS-8873 TFA is the TFA salt form of GS-8873. GS-8873 TFA is an orally active inhibitor for the production of hepatitis B virus ( HBV ) surface antigen ( HBsAg ) with an EC 50 of 4 nM. GS-8873 TFA exhibits good pharmacokinetic characters in rats and metabolic stability in human hepatocytes. GS-8873 TFA causes neurofunctional deficits in rats and cynomolgus monkeys.