PSI-7977 is a prodrug that is metabolized to the active antiviral agent 2'-deoxy-2'-α-fluoro-β-C-methyluridine-5'-monophosphate and is currently being investigated in phase 3 clinical trials for the t
reatment of hepatitis C. Studies have profiled PSI-7977 as a nucleotide inhibitor of hepatitis C virus, exerting selective inhibitory effects towards HCV NS5B polymerase.
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Oral sofosbuvir was generally well tolerated in patients with chronic hepatitis C. The most commonly reported adverse events and laboratory abnormalities in patients receiving sofosbuvir plus ribavirin with or without peginterferon-alpha were consistent with those expected in patients receiving treatment with ribavirin and peginterferon-alpha, and co-administering sofosbuvir did not appear to increase the frequency or severity of these adverse events or laboratory abnormalities.
Dosage and administration
In the US, oral sofosbuvir is approved for the treatment of chronic hepatitis C as a component of a combination antiviral treatment regimen (monotherapy with sofosbuvir is not recommended). US prescribing information states that the efficacy of sofosbuvir has been established in patients with HCV genotype 1, 2, 3 or 4 infection, including patients with HCC meeting Milan criteria (awaiting liver transplantation) and patients co-infected with HCV and HIV-1.
In the EU, oral sofosbuvir is approved for use in combination with other medicinal products for the treatment of chronic hepatitis C in adults. The recommended sofosbuvir dosage is 400 mg once daily[11, 12]. US prescribing information states that sofosbuvir should be taken with or without food and the EU SPC states that it should be taken with food.
In the US, it is recommended that sofosbuvir be administered for 12 weeks in combination with peginterferon-a and ribavirin in chronic HCV genotype 1 or 4 infection, for 12 weeks in combination with ribavirin in chronic HCV genotype 2 infection and for 24 weeks in combination with ribavirin in chronic HCV genotype 3 infection. Treatment with sofosbuvir plus ribavirin for 24 weeks can also be considered an option in patients with chronic HCV genotype 1 infection who are not eligible to receive interferon-based treatment. To prevent post-transplant HCV reinfection in patients with HCC who are awaiting liver transplantation, combination therapy with sofosbuvir plus ribavirin is recommended for up to 48 weeks or until the time of liver transplantation, whichever occurs first.
In the EU, it is recommended that sofosbuvir be administered for 12 weeks in combination with peginterferon-alpha and ribavirin in chronic HCV genotype 1, 4, 5 or 6 infection, with 24 weeks’ therapy with sofosbuvir plus ribavirin only an option for patients with HCV genotype 1, 4, 5 or 6 infection if they are ineligible for, or intolerant of, treatment with peginterferon-alpha. It is recommended that patients with chronic HCV genotype 2 infection receive sofosbuvir plus ribavirin for 12 weeks, and that patients with chronic HCV genotype 3 infection receive sofosbuvir plus peginterferon-alpha and ribavirin for 12 weeks or sofosbuvir plus ribavirin for 24 weeks. In patients with chronic hepatitis C awaiting liver transplantation, sofosbuvir plus ribavirin should be administered until the time of liver transplantation.
ChEBI: A nucleotide conjugate that is used in combination with ledipasvir (under the trade name Harvoni) for the treatment of chronic hepatitis C genotype 1 infection.
Mechanism of action and resistance
Sofosbuvir is a pyrimidine nucleotide analogue (Fig. 1) that inhibits HCV NS5B RNA-dependent RNA polymerase, which is essential for viral replication[11, 12], Sofosbuvir is a prodrug that undergoes intracellular metabolism in human hepatocytes to a pharmacologically active uridine triphosphate form (GS-461203)[11-14]. GS-461203 is incorporated into HCV RNA by NS5B polymerase where it acts as a chain terminator[11, 12]. In vitro, the GS-461203 concentration leading to 50 % inhibition of the polymerase activity of recombinant NS5B from HCV genotype 1b, 2a, 3a and 4a ranged from 0.7 to 2.6 micromolar per liter. A rapid rate of viral decline was seen with Sofosbuvir. It was estimated that 99 and 99.9 % of final effectiveness would be reached in a mean 0.8 and 2 days, respectively. HCV RNA levels declined in a biphasic manner.
Sofosbuvir has a high genetic barrier to resistance. Studies have found that resistance-associated variants (including the primary sofosbuvir resistance mutation in NS5B, S282T) were not detected in any patient receiving sofosbuvir in combination with ribavirin with or without peginterferon-alpha[15, 16]. However, the S282T resistance mutation was detected in one patient with HCV genotype 2b infection who received sofosbuvir monotherapy. Although L159F and V321A substitutions were detected in some patients with HCV genotype 3a infection who received sofosbuvir-containing regimens in phase III trials, these substitutions were not associated with changes in phenotypic susceptibility of sofosbuvir. In patients with HCV genotype 1a or 2b infection and HCC who received sofosbuvir and ribavirin for up to 48 weeks while awaiting liver transplantation, the L159F substitution emerged in multiple patients who experienced virological failure (breakthrough and relapse). The presence of L159F and/or C316N substitutions at baseline was also associated with post-transplant virological breakthrough and relapse in multiple patients with HCV genotype 1b infection.
HCV replicons expressing the S282T resistance mutation showed low level resistance to sofosbuvir, but retained susceptibility to ribavirin and other classes of direct-acting antivirals, including NS5A inhibitors. Sofosbuvir retained full activity against the nucleoside inhibitor resistance-associated variants L159F and L320F, the ribavirin resistance-associated variants T390I and F415Y, and against clinically relevant protease inhibitor, non-nucleoside inhibitor and NS5A inhibitor resistance-associated variants[18, 19]
GS-331007 is the predominant circulating metabolite of sofosbuvir and accounts for 90 % of systemic exposure, with sofosbuvir accounting for & 4 %.
Sofosbuvir was rapidly absorbed following oral administration, with maximum plasma concentrations (Cmax) of sofosbuvir and GS-331007 achieved at ~ 0.5–2 h and 2–4 h post-dose, respectively[11, 12]. In patients with HCV genotype 1–6 infection who received sofosbuvir plus ribavirin with or without peginterferon-alpha, the steady-state geometric mean area under the plasma concentration-time curve (AUC) from time zero to 24 h (AUC24) for sofosbuvir and GS-331007 was 828 and 6,790 ng * h/mL, respectively. The mean sofosbuvir AUC was 36 % higher and the mean GS-331007 AUC was 39 % lower in patients with chronic HCV infection than in healthy volunteers.
The rate of sofosbuvir absorption was slowed and the extent of absorption was increased & 1.8-fold when sofosbuvir was administered with a high-fat meal, rather than in the fasting state; GS-331007 exposure was not altered. The US prescribing information states that sofosbuvir may be administered without regard to food, whereas the EU SPC states that sofosbuvir should be administered with food.
Sofosbuvir was ~ 61–65 % bound to human plasma proteins, whereas plasma protein binding of GS-331007 was minimal.
Sofosbuvir undergoes extensive hepatic metabolism to a pharmacologically active uridine triphosphate form (GS-461203)[11-13]. Dephosphorylation results in the formation of GS-331007, which did not show anti-HCV activity in vitro[11, 12].
Renal clearance is the major elimination pathway for GS-331007[11, 12]. Following administration of a single radiolabelled dose of sofosbuvir 400 mg, ~80 and 14 % of the radioactivity was recovered in the urine and faeces, respectively[11, 12].
Sofosbuvir had a median terminal elimination half-life (t_1/2) of 0.4 h and GS-331007 had a t_1/2 of 27 h[11, 12].
Sofosbuvir is a substrate of P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), although GS- 331007 is not[11, 12]. Thus, it is expected that sofosbuvir concentrations may be reduced by coadministration of sofosbuvir and potent intestinal P-gp inducers[11, 12]. Given this, the EU SPC states that sofosbuvir should not be coadministered with the potent intestinal P-gp inducers carbamazepine, phenytoin, phenobarbital, oxcarbazepine, rifampicin or Hypericum perforatum (St John’s wort). In addition, coadministration of sofosbuvir and rifabutin or rifapentine is not recommended. The US prescribing information states that rifampicin and H. perforatum should not be used with sofosbuvir, and that coadministration of sofosbuvir and carbamazepine, phenytoin, phenobarbital, oxcarbazepine, rifabutin or rifapentine is not recommended.
Sofosbuvir is a drug used for the treatment of hepatitis C. It is recommended to be used in combination with other drugs (such as velpatasvir) for the first-line treatment for HCV genotypes 1, 2, 3, 4, 5, and 6. It takes effect through acting as a nucleotide analog inhibitor, being capable of specially inhibiting the HCV NS5B (non-structural protein 5B) RNA-dependent RNA polymerase.
PSI-7977 is a phosphoramidate prodrug of PSI-7851, a nucleoside analog that, when phosphorylated, inhibits the RNA-dependent RNA polymerase of hepatitis C virus (EC50 = 92 nM). PSI-7977 is effective in vitro and in vivo.[Cayman Chemical]