NS5A inhibitors are a family of drugs ( e.g. ledipasvir, velpatasvir, daclatasvir, ombitasvir and others) which are used to treat viral infections such as Hepatitis C.

In combination, they have 'cure' rates over 90%. They disrupt the action of the Nonstructural protein 5A(NS5A) which is crucial in the viral 'life cycle'.

How this works in practice is currently unknown.

NS5A inhibitors have been developed to target the NS5A protein. These inhibitors have achieved a significant reduction in HCV RNA blood levels and can therefore be considered as potent antivirals. Their mechanism of action is thought to be diverse but the exact mechanism is not fully understood. Most studies assume that NS5A inhibitors act on two essential stages of the HCV life cycle; the replication of the genomic RNA, and virion assembly. Other studies propose an alteration of host cell factors as a possible third mechanism.

Source : Wikipedia