Sofosbuvir works by inhibiting a key enzyme (NS5B RNA-dependent RNA polymerase) needed for the Hepatitis C virus to replicate. After Darvoni enters the body, Sofosbuvir becomes an active compound that blocks the virus from making copies of its RNA. Darvoni does this by stopping the viral RNA chain from growing. Daclatasvir works by blocking a protein (NS5A) in the virus that is necessary for the virus to make more of itself and to produce proteins.