NS5A Resistance: Clinical Implications and Treatment Possibilities.

Treatments with interferon-free direct-acting antiviral agents have high efficacy, with sustained virological response rates of more than 90%. Nevertheless, they fail to eliminate the infection in 1-7% of patients. The majority of virological failures are due to relapse following treatment discontinuation, while virological rebound during therapy is rare. Although not the only factor, the presence of resistance-associated variants is one of the major causes for said failure. Resistance-associated variants affect the sequence involved in protein synthesis on which different direct-acting antiviral agents act (NS3/4A, NS5A, NS5B). Of all these variants, the ones with the greatest impact are resistance-associated variants that affect the NS5A region due to their long-term persistence. In this article we will describe the most significant NS5A resistance-associated variants, the clinical relevance of their detection both before and after treatment, their persistence over time, and lastly, we will devote particular attention to discussing what approach to adopt when dealing with treatment failure to an antiviral regimen that includes NS5A inhibitors.