PSI-7977 is an experimental drug candidate for the treatment of hepatitis C

Hepatitis C

Hepatitis C is an infectious disease primarily affecting the liver, caused by the hepatitis C virus . The infection is often asymptomatic, but chronic infection can lead to scarring of the liver and ultimately to cirrhosis, which is generally apparent after many years...

. It is under development by Pharmasset

Pharmasset

Pharmasset Inc. is a pharmaceutical company based in Princeton, New Jersey in the United States. The company develops antiviral drugs for HIV , hepatitis B , and hepatitis C. In November 2011, Pharmasset was acquired by Gilead for $11 billion.-History:Pharmasset was founded in 1998 by Dr. Raymond...

 and is currently in Phase II clinical trials. It is being studied as a treatment to be used in combination with ribavirin

Ribavirin

Ribavirin is an anti-viral drug indicated for severe RSV infection , hepatitis C infection and other viral infections. Ribavirin is a prodrug, which when metabolised resembles purine RNA nucleotides...

.

PSI-7977 is a prodrug

Prodrug

A prodrug is a pharmacological substance administered in an inactive form. Once administered, the prodrug is metabolised in vivo into an active metabolite, a process termed bioactivation. The rationale behind the use of a prodrug is generally for absorption, distribution, metabolism, and...

that is metabolized to the active antiviral agent 2'-deoxy-2'-α-fluoro-β-C-methyluridine-5'-monophosphate.