INF a was used in the mid of 1980s for treatment of NANB chronic hepatitis, after the discovery of HCV in 1998, INFa monotherapy was considered the standard of care treatment of chronic hepatitis C. This is followed by the addition of ribavirin and later pegylated INF was discovered and its combination to ribavirin was considered the standard of care treatment for CHC. I think the use of standard or conventional was newly addressed after the discovery of pegylated INFa
Pegylations offers increasing the molecular mass of proteins and peptides and shielding them from proteolytic enzymes and improves their pharmacokinetics
Pegylation led to improvement in not only pharmacokinetics but also pharmacodynamics of IFN which can be explained by the improved patient response. Pegylated IFN is a novel product hence, IFN without pegylation is termed as coventional/standard/classical IFN.