Nucleos(t)ide analogues have proven useful in the treatment of viral infections. Ribavirin is a nucleoside, guanosine analogue, whose mechanisms of action include inhibition of inosine monophosphate dehydrogenase (IMPDH), which is the key step in de novo guanine synthesis, a requirement for viral replication. In combination with pegylated interferon alfa, ribavirin is the standard of care for the treatment of chronic hepatitis C today. However, the medication is associated with significant haemolytic anaemia, which may require dose reduction, discontinuation or treatment with recombinant human erythropoietin. Dose reduction also appears to decrease sustained viral clearance rates. Newer IMPDH inhibitors are in various stages of development. Viramidine, a liver-targeting prodrug of ribavirin, has demonstrated significant antiviral activity and erythrocyte-sparing properties. It is currently in Phase 3 trials. Clinical trials of merimepodib, another investigational IMPDH inhibitor, have completed enrolment for a Phase 2b study as a third medication for administration with pegylated interferon plus ribavirin. Although other IMDPH inhibitors also have antiviral activity, these medications appear best suited as immunosuppressive medications at this time.