Table 1.

Antiviral Resistance Nomenclature

Term	Definition
Primary treatment failure (nonresponse)	<1 log decline in HBV DNA 12 weeks after starting therapy
Secondary treatment failure (virological breakthrough)	≥1 log increase in HBV DNA from nadir in a compliant patient, confirmed with repeat testing at least 1 month later
Biochemical breakthrough	Rise in ALT while on treatment, after having achieved normalization in a compliant patient
Genotypic resistance	Detection of viral populations bearing reverse transcriptase mutations previously shown to confer resistance to antiviral drugs in a phenotypic assay
Phenotypic resistance	Decreased susceptibility of an HBV polymerase to antiviral treatment in vitro
Cross‐resistance	Decreased susceptibility to more than one antiviral drug conferred by the same mutation or combination of mutations

Adapted with permission from Hepatology.1 Copyright 2007, Wiley.