The drug viramidine, which is a prodrug of ribavirin that has better targeting for the liver, and therefore may be more effective against hepatitis C for a given tolerated dose, is in phase III experimental trials against hepatitis C. It will be used in conjunction with interferons, in the same manner as ribavirin. However, this drug is not expected to be active against ribavirin-resistant strains, and the use of the drug against infections which have already failed ribavirin/interferon treatment, is unproven.
There are new drugs under development, like the protease inhibitors (including telaprevir/VX 950), entry inhibitors (such as SP 30 and ITX 5061) and polymerase inhibitors (such as RG7128, PSI-7977 and NM 283), but development of some of these is still in the early phase. VX 950, also known as telaprevir was approved by the FDA in 2011. One protease inhibitor, BILN 2061, had to be discontinued due to safety problems early in the clinical testing. Some more modern new drugs that provide some support in treating HCV are albuferon and Zadaxin. Antisense phosphorothioate oligos have been targeted to hepatitis C. Antisense Morpholino oligos have shown promise in preclinical studies however, they were found to cause a limited viral load reduction.
Some studies have shown that HCV viral replication is dependent upon the host factor miR-122. As a result, pharmaceutical companies are developing potential HCV drugs that target miR-122. HCV therapies that target this host factor necessary for viral replication, rather than the virus itself, are promising, as they show little to no potential for viral resistance. One such drug is miravirsen, developed by Santaris Pharma a/s, a locked nucleic acid based miR-122 antagonist in Phase II clinical trials as of late 2010.
Immunoglobulins against the hepatitis C virus exist, and newer types are under development. Thus far, their roles have been unclear, as they have not been shown to help in clearing chronic infection or in the prevention of infection with acute exposures (e.g. needle sticks). They do have a limited role in transplant patients.
In addition to the standard treatment with interferon and ribavirin, some studies have shown higher success rates when the antiviral drug amantadine (Symmetrel) is added to the regimen. Sometimes called "triple therapy", it involves the addition of 100 mg of amantadine twice a day. Studies indicate this may be especially helpful for "nonresponders" — patients who have not been successful in previous treatments using interferon and ribavirin only. Currently, amantadine is not approved for treatment of hepatitis C, and studies are ongoing to determine when it is most likely to benefit the patient and when it is a risk due to their liver deterioration.
Bristol-Myers Squibb has obtained promising Phase II results for its experimental drug, BMS-790052, an NS5A replication complex inhibitor, in combination with peginterferon alfa and ribavirin.