Chemical formula: C₂₆H₂₇N₃O₅S Molecular mass: 493.58 g/mol PubChem compound: 56640146
Dasabuvir is a non-nucleoside inhibitor of the HCV RNA-dependent RNA polymerase encoded by the NS5B gene, which is essential for replication of the viral genome.
Co-administration of dasabuvir with ombitasvir/paritaprevir/ritonavir combines three direct-acting antiviral medicinal products with distinct mechanisms of action and non-overlapping resistance profiles to target HCV at multiple steps in the viral lifecycle.
The EC50 of dasabuvir against genotype 1a-H77 and 1b-Con1 strains in HCV replicon cell culture assays was 7.7 and 1.8 nM, respectively. The replicon activity of dasabuvir was attenuated 12- to 13- fold in the presence of 40% human plasma. The mean EC50 of dasabuvir against replicons containing NS5B from a panel of treatment-naïve genotype 1a and 1b isolates in the HCV replicon cell culture assay was 0.77 nM (range 0.4 to 2.1 nM; n=11) and 0.46 nM (range 0.2 to 2 nM; n=10), respectively. In biochemical assays, dasabuvir inhibited a panel of genotype 1a and 1b polymerases with a mean IC50 value of 4.2 nM (range 2.2 to 10.7 nM; n=7).
The M1 metabolite of dasabuvir had EC50 values of 39 and 8 nM against genotype 1a-H77 and 1bCon1 strains in HCV replicon cell culture assays, respectively, and the activity of the M1 metabolite was attenuated 3- to 4-fold in the presence of 40% human plasma. Dasabuvir had reduced activity in biochemical assays against NS5B polymerases from HCV genotypes 2a, 2b, 3a and 4a (IC50 values ranging from 900 nM to >20 μM).
Resistance to dasabuvir conferred by variants in NS5B 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, substitutions C316Y, M414T, Y448H, A553T, G554S, S556G/R, and Y561H in HCV NS5B reduced susceptibility to dasabuvir. In the genotype 1a replicon, the activity of dasabuvir was reduced 21- to 32-fold by the M414T, S556G or Y561H substitutions; 152- to 261-fold by the A553T, G554S or S556R substitutions; and 1472- and 975-fold by the C316Y and Y448H substitutions, respectively. G558R and D559G/N were observed as treatment-emergent substitutions but the activity of dasabuvir against these variants could not be evaluated due to poor replication capacity. In genotype 1b, substitutions C316N, C316Y, M414T, Y448H, and S556G in HCV NS5B reduced susceptibility to dasabuvir. The activity of dasabuvir was reduced by 5- and 11-fold by C316N and S556G, respectively; 46-fold by M414T or Y448H; and 1569-fold by the C316Y substitutions in the genotype 1b replicon. Dasabuvir retained full activity against replicons containing substitutions S282T in the nucleoside binding site, M423T in the lower thumb site, and P495A/S, P496S or V499A in the upper thumb site.
A pooled analysis of subjects with genotype 1 HCV infection, who were treated with dasabuvir, ombitasvir and paritaprevir with or without ribavirin in Phase 2b and 3 clinical trials, was conducted to explore the association between baseline NS3/4A, NS5A or NS5B substitutions/polymorphisms and treatment outcome in these recommended regimens.
In the greater than 500 genotype 1a baseline samples in this analysis, the most frequently observed resistance-associated variants were M28V (7.4%) in NS5A and S556G (2.9%) in NS5B. Q80K, although a highly prevalent polymorphism in NS3 (41.2% of samples), confers minimal resistance to paritaprevir. Resistance-associated variants at amino acid positions R155 and D168 in NS3 were rarely observed (less than 1%) at baseline. In the greater than 200 genotype 1b baseline samples in this analysis, the most frequently observed resistance-associated variants observed were Y93H (7.5%) in NS5A, and C316N (17.0%) and S556G (15%) in NS5B. Given the low virologic failure rates observed with recommended treatment regimens for HCV genotype 1a- and 1b-infected subjects, the presence of baseline variants appears to have little impact on the likelihood of achieving SVR.
The persistence of dasabuvir, ombitasvir and paritaprevir resistance-associated amino acid substitutions in NS5B, NS5A and NS3, respectively, was assessed in genotype 1a-infected subjects in Phase 2b trials. Dasabuvir treatment-emergent variants M414T, G554S, S556G, G558R or D559G/N in NS5B were observed in 34 subjects. Ombitasvir treatment-emergent variants M28T, M28V or Q30R in NS5A were observed in 32 subjects. Paritaprevir treatment-emergent variants V36A/M, R155K or D168V were observed in NS3 in 47 subjects.
NS3 variants V36A/M and R155K and NS5B variants M414T and S556G remained detectable at posttreatment Week 48, whereas NS3 variant D168V and all other NS5B variants were not observed at post-treatment Week 48. All treatment-emergent variants in NS5A remained detectable at posttreatment Week 48. Due to high SVR rates in genotype 1b, trends in persistence of treatment-emergent variants in this genotype could not be established.
The lack of detection of virus containing a resistance-associated substitution does not indicate that the resistant virus is no longer present at clinically significant levels. The long-term clinical impact of the emergence or persistence of virus containing dasabuvir and ombitasvir/paritaprevir/ritonavir – resistance-associated substitutions on future treatment is unknown.
Cross-resistance is expected among NS5A inhibitors, NS3/4A protease inhibitors, and non-nucleoside NS5B inhibitors by class. The impact of prior dasabuvir, ombitasvir, or paritaprevir treatment experience on the efficacy of other NS5A inhibitors, NS3/4A protease inhibitors, or NS5B inhibitors has not been studied.
The pharmacokinetic properties of the combination of dasabuvir with ombitasvir/paritaprevir/ritonavir have been evaluated in healthy adult subjects and in subjects with chronic hepatitis C. Table 18 shows mean Cmax and AUC of dasabuvir 250 mg twice daily with ombitasvir/paritaprevir/ritonavir 25 mg/150 mg/100 mg once daily following multiple doses with food in healthy volunteers.
Geometric mean Cmax, AUC of multiple doses of dasabuvir 250 mg twice daily and ombitasvir/paritaprevir/ritonavir 25 mg/150 mg/100 mg once daily with food in healthy volunteers:
| Cmax (ng/ml) (CV%) | AUC (ng*hr/ml) (CV%) | |
|---|---|---|
| Dasabuvir | 1030 (31) | 6840 (32) |
Dasabuvir was absorbed after oral administration with mean Tmax of approximately 4 to 5 hours. Dasabuvir exposures increased in a dose proportional manner and accumulation is minimal. Pharmacokinetic steady state for dasabuvir when coadministered with ombitasvir/paritaprevir/ritonavir is achieved after approximately 12 days of dosing.
Dasabuvir should be administered with food. All clinical trials with dasabuvir have been conducted following administration with food.
Food increased the exposure (AUC) of dasabuvir by up to 30% relative to the fasting state. The increase in exposure was similar regardless of meal type (e.g., high-fat versus moderate-fat) or calorie content (approximately 600 kcal versus approximately 1000 kcal). To maximise absorption, dasabuvir should be taken with food without regard to fat or calorie content.
Dasabuvir is highly bound to plasma proteins. Plasma protein binding is not meaningfully altered in patients with renal or hepatic impairment. The blood to plasma concentration ratios in human ranged from 0.5 to 0.7 indicating that dasabuvir was preferentially distributed in the plasma compartment of whole blood. Dasabuvir was greater than 99.5%, and M1 major metabolite of dasabuvir was 94.5% bound to human plasma proteins over a concentration range of 0.05 to 5 µg/mL. At steady-state the exposures ratio of M1 to dasabuvir is approximately 0.6. Taking into account the protein binding and in vitro activity of M1 against HCV genotype 1, its contribution to efficacy is expected to be similar to that of dasabuvir. In addition, M1 is a substrate of the hepatic uptake transporters OATP family and OCT1 and thus, the hepatocyte concentration and thereby contribution to efficacy, may be larger than dasabuvir.
Dasabuvir is predominantly metabolised by CYP2C8 and to a lesser extent by CYP3A. Following a 400 mg 14C-dasabuvir dose in humans, unchanged dasabuvir was the major component (approximately 60%) of drug related radioactivity in plasma. Seven metabolites were identified in plasma. The most abundant plasma metabolite was M1, which represented 21% of drug-related radioactivity (AUC) in circulation following single dose; it’s formed via oxidative metabolism predominantly by CYP2C8.
Following dosing of dasabuvir with ombitasvir/paritaprevir/ritonavir, mean plasma half-life of dasabuvir was approximately 6 hours. Following a 400 mg 14C-dasabuvir dose, approximately 94% of the radioactivity was recovered in faeces with limited radioactivity (approximately 2%) in urine. Unchanged dasabuvir accounted for 26.2% and M1 for 31.5% of the total dose in faeces. M1 is mainly cleared through direct biliary excretion with the contribution of UGT-mediated glucuronidation and, to a small extent, oxidative metabolism.
Dasabuvir does not inhibit organic anion transporter (OAT1) in vivo and is not expected to inhibit organic cation transporters (OCT2), organic anion transporters (OAT3), or multidrug and toxin extrusion proteins (MATE1 and MATE2K) at clinically relevant concentrations; therefore, dasabuvir does not affect medicinal product transport by these proteins.
Based on population pharmacokinetic analysis of data from Phase 3 clinical studies, a 10 year increase or decrease in age from 54 years (median age in the Phase 3 studies) would results in <10% change in dasabuvir exposures. There is no pharmacokinetic information in patients >75 years.
Based on population pharmacokinetic analysis of data from Phase 3 clinical studies, female subjects would have approximately 14 to 30% higher dasabuvir exposures than male subjects. A 10 kg change in body weight from 76 kg (median weight in the Phase 3 studies) would result in <10% change in dasabuvir exposures.
Based on population pharmacokinetic analysis of data from Phase 3 clinical studies, Asian subjects had 29% to 39% higher dasabuvir exposures than non-Asian subjects.
Pharmacokinetics of the combination of ombitasvir 25 mg, paritaprevir 150 mg, and ritonavir 100 mg, with dasabuvir 400 mg were evaluated in subjects with mild (CrCl: 60 to 89 ml/min), moderate (CrCl: 30 to 59 ml/min) and severe (CrCl: 15 to 29 ml/min) renal impairment, relative to subjects with normal renal function.
In subjects with mild, moderate and severe renal impairment, dasabuvir mean AUC values were 21% higher, 37% higher and 50% higher, respectively. Dasabuvir M1 AUC values were 6% lower, 10% lower, and 13% lower, respectively.
The changes in dasabuvir exposures in subjects with mild, moderate and severe renal impairment are not considered to be clinically significant. Limited data in patients with end-stage renal disease indicate no clinically significant changes in exposure also in this patient group. No dose adjustment of dasabuvir is required for patients with mild, moderate, or severe renal impairment, or end-stage-renal disease on dialysis.
Pharmacokinetics of the combination of dasabuvir 400 mg, with ombitasvir 25 mg, paritaprevir 200 mg, and ritonavir 100 mg were evaluated in subjects with mild (Child-Pugh A), moderate (ChildPugh B) and severe (Child-Pugh C) hepatic impairment, relative to subjects with normal hepatic function.
In subjects with mild, moderate and severe hepatic impairment, dasabuvir AUC values were 17% higher, 16% lower and 325% higher, respectively. The AUC values of dasabuvir M1 metabolite were unchanged, 57% lower, and 77% higher, respectively. Plasma protein binding of dasabuvir and its M1 metabolite were not meaningfully different in subjects with hepatic impairment compared to normal control subjects.
The pharmacokinetics of dasabuvir with ombitasvir/paritaprevir/ritonavir in paediatric patients has not been investigated.
Dasabuvir was not genotoxic in a battery of in vitro or in vivo assays, including bacterial mutagenicity, chromosome aberration using human peripheral blood lymphocytes and in vivo rat micronucleus assays.
Dasabuvir was not carcinogenic in a 6-month transgenic mouse study up to the highest dosage tested (2 g/kg/day), resulting in dasabuvir AUC exposures approximately 19-fold higher than those in humans at the recommended dose of 500 mg (250 mg twice daily).
Similarly, dasabuvir was not carcinogenic in a 2-year rat study up to the highest dose tested (800 mg/kg/day), resulting in dasabuvir exposures approximately 19-fold higher than those in humans at 500 mg.
Dasabuvir had no effects on embryo-foetal viability or on fertility in rodents and were not teratogenic in two species. No adverse effects on behaviour, reproduction or development of offspring were reported. The highest dasabuvir dose tested produced exposures equal to 16 to 24-fold (rat) or 6-fold (rabbit) the exposures in humans at the maximum recommended clinical dose.
Dasabuvir was the predominant component observed in the milk of lactating rats, without effect on nursing pups. Elimination half-life in rat milk was slightly shorter than in plasma, AUC was about 2 fold of that in plasma. Since dasabuvir is a BCRP substrate, distribution to the milk may change if this transporter is inhibited or induced by co-administration of other medicinal products. Dasabuvirderived material was minimally transferred through the placenta in pregnant rats.
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