Pharmacotherapeutic group: Antivirals for systemic use; direct-acting antivirals, ATC code: not yet assigned
Mechanism of action
Viekirax, when co-administered with dasabuvir, combines three direct-acting antiviral agents with distinct mechanisms of action and non-overlapping resistance profiles to target HCV at multiple steps in the viral lifecycle. Refer to the Summary of Product Characteristics of dasabuvir for its pharmacological properties.
Ritonavir
Ritonavir is not active against HCV. Ritonavir is a CYP3A inhibitor that increases the systemic exposure of the CYP3A substrate paritaprevir.
Ombitasvir
Ombitasvir is an inhibitor of HCV NS5A which is essential for viral replication.
Paritaprevir
Paritaprevir is an inhibitor of HCV NS3/4A protease which is necessary for the proteolytic cleavage of the HCV encoded polyprotein (into mature forms of the NS3, NS4A, NS4B, NS5A, and NS5B proteins) and is essential for viral replication.
Activity in cell culture and/or biochemical studies
Ombitasvir
The EC50 of ombitasvir against genotype 1a-H77 and 1b-Con1 strains in HCV replicon cell culture assays was 14.1 and 5 pM, respectively. The activity of ombitasvir was attenuated 11- to 13-fold in the presence of 40% human plasma. The mean EC50 of ombitasvir against replicons containing NS5A from a panel of treatment-naïve genotype 1a and 1b isolates in the HCV replicon cell culture assay was 0.66 pM (range 0.35 to 0.88 pM; n=11) and 1.0 pM (range 0.74 to 1.5 pM; n=11), respectively. Ombitasvir has EC50 values of 12, 4.3, 19, 1.7, 3.2, and 366 pM against replicon cell lines constructed with NS5A from single isolates representing genotypes 2a, 2b, 3a, 4a, 5a, and 6a, respectively.
Paritaprevir
The EC50 of paritaprevir against genotype 1a-H77 and 1b-Con1 strains in the HCV replicon cell culture assay was 1.0 and 0.21 nM, respectively. The activity of paritaprevir was attenuated 24 to 27 -fold in the presence of 40% human plasma. The mean EC50 of paritaprevir against replicons containing NS3 from a panel of treatment-naïve genotype 1a and 1b isolates in the HCV replicon cell culture assay was 0.86 nM (range 0.43 to 1.87 nM; n=11) and 0.06 nM (range 0.03 to 0.09 nM; n=9), respectively. Paritaprevir had an EC50 value of 5.3 nM against the 2a-JFH-1 replicon cell line, and EC50 values of 19, 0.09, and 0.68 nM against replicon cell lines containing NS3 from a single isolate each of genotype 3a, 4a, and 6a, respectively
Ritonavir did not exhibit a direct antiviral effect on the replication of HCV subgenomic replicons, and the presence of ritonavir did not affect the in vitro antiviral activity of paritaprevir.
Resistance
In cell culture
Genotype 1
Resistance to paritaprevir and ombitasvir conferred by variants in NS3 and NS5A respectively, selected in cell culture or identified in Phase 2b and 3 clinical trials were phenotypically characterised in the appropriate genotype 1a or 1b replicons.
In genotype 1a, subs
