Structural Basis for RNA Replication by the SARS-CoV-2 Polymerase.

Nucleotide analog inhibitors, including broad-spectrum remdesivir and favipiravir, have shown promise in in vitro assays and some clinical studies for COVID-19 treatment, this despite an incomplete mechanistic understanding of the viral RNA-dependent RNA polymerase nsp12 drug interactions. Here, we examine the molecular basis of SARS-CoV-2 RNA replication by determining the cryo-EM structures of the stalled pre- and post- translocated polymerase complexes. Compared with the apo complex, the structures show notable structural rearrangements happening to nsp12 and its co-factors nsp7 and nsp8 to accommodate the nucleic acid, whereas there are highly conserved residues in nsp12, positioning the template and primer for an in-line attack on the incoming nucleotide. Furthermore, we investigate the inhibition mechanism of the triphosphate metabolite of remdesivir through structural and kinetic analyses. A transition model from the nsp7-nsp8 hexadecameric primase complex to the nsp12-nsp7-nsp8 polymerase complex is also proposed to provide clues for the understanding of the coronavirus transcription and replication machinery.

Induced intra- and intermolecular template switching as a therapeutic mechanism against RNA viruses.

Viral RNA-dependent RNA polymerases (RdRps) are a target for broad-spectrum antiviral therapeutic agents. Recently, we demonstrated that incorporation of the T-1106 triphosphate, a pyrazine-carboxamide ribonucleotide, into nascent RNA increases pausing and backtracking by the poliovirus RdRp. Here, by monitoring enterovirus A-71 RdRp dynamics during RNA synthesis using magnetic tweezers, we identify the "backtracked" state as an intermediate used by the RdRp for copy-back RNA synthesis and homologous recombination. Cell-based assays and RNA sequencing (RNA-seq) experiments further demonstrate that the pyrazine-carboxamide ribonucleotide stimulates these processes during infection. These results suggest that pyrazine-carboxamide ribonucleotides do not induce lethal mutagenesis or chain termination but function by promoting template switching and formation of defective viral genomes. We conclude that RdRp-catalyzed intra- and intermolecular template switching can be induced by pyrazine-carboxamide ribonucleotides, defining an additional mechanistic class of antiviral ribonucleotides with potential for broad-spectrum activity.

Favipiravir induces HuNoV viral mutagenesis and infectivity loss with clinical improvement in immunocompromised patients.

Chronic human norovirus (HuNoV) infections in immunocompromised patients result in severe disease, yet approved antivirals are lacking. RNA-dependent RNA polymerase (RdRp) inhibitors inducing viral mutagenesis display broad-spectrum in vitro antiviral activity, but clinical efficacy in HuNoV infections is anecdotal and the potential emergence of drug-resistant variants is concerning. Upon favipiravir (and nitazoxanide) treatment of four immunocompromised patients with life-threatening HuNoV infections, viral whole-genome sequencing showed accumulation of favipiravir-induced mutations which coincided with clinical improvement although treatment failed to clear HuNoV. Infection of zebrafish larvae demonstrated drug-associated loss of viral infectivity and favipiravir treatment showed efficacy despite occurrence of RdRp variants potentially causing favipiravir resistance. This indicates that within-host resistance evolution did not reverse loss of viral fitness caused by genome-wide accumulation of sequence changes. This off-label approach supports the use of mutagenic antivirals for treating prolonged RNA viral infections and further informs the debate surrounding their impact on virus evolution.

Favipiravir, remdesivir, and lopinavir: metabolites, degradation products and their analytical methods.

Severe acute respiratory syndrome 2 (SARS-CoV-2) caused the emergence of the COVID-19 pandemic all over the world. Several studies have suggested that antiviral drugs such as favipiravir (FAV), remdesivir (RDV), and lopinavir (LPV) may potentially prevent the spread of the virus in the host cells and person-to-person transmission. Simultaneously with the widespread use of these drugs, their stability and action mechanism studies have also attracted the attention of many researchers. This review focuses on the action mechanism, metabolites and degradation products of these antiviral drugs (FAV, RDV and LPV) and demonstrates various methods for their quantification and discrimination in the different biological samples. Herein, the instrumental methods for analysis of the main form of drugs or their metabolite and degradation products are classified into two types: optical and chromatography methods which the last one in combination with various detectors provides a powerful method for routine and stability analyses. Some representative studies are reported in this review and the details of them are carefully explained. It is hoped that this review will be a good guideline study and provide a better understanding of these drugs from the aspects investigated in this study.

Identification of dihydroorotate dehydrogenase inhibitor, vidofludimus, as a potent and novel inhibitor for influenza virus.

Influenza A virus (IAV) infection causes respiratory disease. Recently, infection of IAV H5N1 among mammals are reported in farmed mink. Therefore, to discover antivirals against IAV, we screened a compound library by using the RNA-dependent RNA polymerase (RdRp) assay system derived from H5N1 IAV including a drug-resistant PA mutant (I38T) and a viral polymerase activity enhancing PB2 mutant (T271A). Upon screening, we found vidofludimus can be served as a potential inhibitor for IAV. Vidofludimus an orally active inhibitor for dihydroorotate dehydrogenase (DHODH), a key enzyme for the cellular de novo pyrimidine biosynthesis pathway. We found that vidofludimus exerted antiviral activity against wild-type and drug-resistant mutant IAV, with effective concentrations (EC50 ) of 2.10 and 2.11 µM, respectively. The anti-IAV activity of vidofludimus was canceled by the treatment of uridine or cytidine through pyrimidine salvage synthesis pathway, or orotic acid through pyrimidine de novo synthesis pathway. This indicated that the main target of vidofludimus is DHODH in IAV RdRp expressing cells. We also produced recombinant seasonal IAV H1N1 virion and influenza B virus (IBV) RdRp assay system and confirmed vidofludimus also carried highly antiviral activity against seasonal IAV and IBV. Vidofludimus is a candidate drug for the future threat of IAV H5N1 infection among humans as well as seasonal influenza virus infection.

Clinical antiviral efficacy of favipiravir in early COVID-19 (PLATCOV): an open-label, randomised, controlled, adaptive platform trial.

In early symptomatic COVID-19 treatment, high dose oral favipiravir did not accelerate viral clearance. BACKGROUND: Favipiravir, an anti-influenza drug, has in vitro antiviral activity against SARS-CoV-2. Clinical trial evidence to date is inconclusive. Favipiravir has been recommended for the treatment of COVID-19 in some countries. METHODS: In a multicentre open-label, randomised, controlled, adaptive platform trial, low-risk adult patients with early symptomatic COVID-19 were randomised to one of ten treatment arms including high dose oral favipiravir (3.6g on day 0 followed by 1.6g daily to complete 7 days treatment) or no study drug. The primary outcome was the rate of viral clearance (derived under a linear mixed-effects model from the daily log10 viral densities in standardised duplicate oropharyngeal swab eluates taken daily over 8 days [18 swabs per patient]), assessed in a modified intention-to-treat population (mITT). The safety population included all patients who received at least one dose of the allocated intervention. This ongoing adaptive platform trial was registered at ClinicalTrials.gov (NCT05041907) on 13/09/2021. RESULTS: In the final analysis, the mITT population contained data from 114 patients randomised to favipiravir and 126 patients randomised concurrently to no study drug. Under the linear mixed-effects model fitted to all oropharyngeal viral density estimates in the first 8 days from randomisation (4,318 swabs), there was no difference in the rate of viral clearance between patients given favipiravir and patients receiving no study drug; a -1% (95% credible interval: -14 to 14%) difference. High dose favipiravir was well-tolerated. INTERPRETATION: Favipiravir does not accelerate viral clearance in early symptomatic COVID-19. The viral clearance rate estimated from quantitative measurements of oropharyngeal eluate viral densities assesses the antiviral efficacy of drugs in vivo with comparatively few studied patients.

Assessment of toxicological effects of favipiravir (T-705) on the lung tissue of rats: An experimental study.

This study aimed to present new data on the side effects of favipiravir on healthy lung tissue and the respiratory system. In the study, two different durations (5 and 10 days) were preferred to determine the effect of favipiravir treatment due to clinical improvement rates of approximately 5 and 10 days during the use of favipiravir in COVID-19 patients. In addition, after 10 days of favipiravir treatment, animals were kept for 5 days without any treatment to determine the regeneration of lung tissues. Favipiravir was administered to rats by oral gavage at a daily dose of 200 mg/kg for 5 and 10 days, as in previous studies. At the end of the experiment, the histopathological and biochemical effects of favipiravir in the lung tissue were investigated. The data obtained from the study showed that favipiravir increased oxidative stress parameters, expression of apoptotic markers, and pro-inflammatory markers in lung tissue. Since malondialdehydes is an oxidant parameter, it increased in favipiravir-administered groups; It was determined that the antioxidant parameters glutathione, superoxide dismutase, glutathione peroxidase, and catalase decreased. Other markers used in the analysis are Bcl-2, Bax, NF-κB, interleukin (IL)-6, Muc1, iNOS, P2X7R, IL-6 and caspase-3. The levels of Bax, caspase-3, NF-κB, IL-6, Muc1, and P2X7R were increased in the Fav-treated groups compared with the control. However, the levels of Bcl-2 decreased in the Fav-treated groups. The present study proves that favipiravir, widely used today, causes side effects in lung tissue.

Luminescence of favipiravir in skin appendages and sclera. A controlled study and literature review.

BACKGROUND/OBJECTIVES: Favipiravir is an antiviral agent, recently used for COVID-19 infections. Several reports associate favipiravir intake with Wood's lamp fluorescence of hair, nails, and sclera. The present study was designed to elucidate the positivity rates, and sites of favipiravir-related fluorescence and to unravel the site-specific changes in fluorescence positivity rates by a function of time past exposure. METHODS: The study population comprised 50 patients and 50 control individuals. All patients in the patient group had received a full dose of favipiravir for COVID-19 infection. Fifty volunteers served as the control group. Wood's lamp examination was performed in a completely darkened room, and the positivity rate, extent, pattern, and distribution of fluorescence were recorded. RESULTS: Wood's light revealed fluorescence of the fingernails, toenails, sclera, and hair in 35 (70%), 35 (70%), 22 (44%), and 8 (16%) patients, respectively. No control individual tested positive by Wood's lamp. Statistical analysis revealed significant differences between patient and control groups in terms of Wood's light luminescence in the fingernails (p = .000), toenails (p = .000), sclera (p = .000) and hair (p = .003). Although fingernail, toenail, and hair fluorescence positivity rates declined or ceased at or after 91 days of favipiravir exposure, ocular fluorescence positivity rates were prolonged up to 188 days. CONCLUSIONS: These findings confirm that favipiravir may produce fluorescence of nails, sclera, and hair, detectable by Wood's light starting from the initial month and peaking at second- and third months following exposure to the medication. Although nail and hair fluorescence tend to abate after 3 months, ocular fluorescence may persist even longer than 6 months after cessation of the medication.

Findings from a discontinued clinical trial of favipiravir in high-risk patients with early-onset COVID-19.

INTRODUCTION: Favipiravir terminates severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replication. Accordingly, early administration of favipiravir to SARS-CoV-2-infected coronavirus disease 2019 (COVID-19) patients may be expected to suppress disease progression. METHODS: A randomized double-blind placebo-controlled trial was conducted to demonstrate efficacy of favipiravir in reducing disease progression in patients with mild COVID-19. The participants were unvaccinated patients with comorbidities and at risk of progression to severe disease. Patients were enrolled within 72 h of disease onset and randomized to receive either favipiravir (1800 mg/dose on Day 1 followed by 800 mg/dose) or matching placebo twice daily for 10 days. The primary endpoint was the proportion of patients requiring oxygen therapy within 28 days of randomization. RESULTS: The trial was discontinued after enrolling 84 patients due to slower than anticipated enrollment caused by rapid uptake of SARS-CoV-2-vaccines and the emergence of the Omicron variant. Results from the 84 patients demonstrated no significant difference in all clinical outcomes. In post-hoc analyses, favipiravir treatment showed higher efficacy in patients within 48 h of onset. No deaths or severe adverse events were documented in the favipiravir group. Plasma concentrations of favipiravir from Day 2 onward were maintained above 40 µg/mL. CONCLUSIONS: Conducting clinical trials for pathogens like SARS-CoV-2 that rapidly accumulate mutations leading to altered disease characteristics carries significant risks unless it can be done in a short period. Therefore, it would be important to prepare the comprehensive clinical trial platform that can appropriately and promptly evaluate drugs even under a pandemic.

A liquid chromatography-tandem mass spectrometry method development for the quantification of favipiravir drug and its related impurities in rat plasma and its application to pharmacokinetic studies.

Favipiravir is an antiviral drug used for the treatment of virus-based diseases such as influenza. In this context, the development of a reliable liquid chromatography-tandem mass spectrometry method for the quantification of the drug and its impurities is necessary, particularly following the COVID-19 pandemic. Chromatographic separation was achieved on an inertial ODS column using gradient elution with a buffer containing triethylamine in high-performance liquid chromatography water and adjusting its pH with formic acid. The mixture of buffer and acetonitrile was used as a mobile phase with a flow rate of 1 ml/min at ambient temperature. The separation of favipiravir and its related impurities from remdesivir as an internal standard was achieved. The results indicated that all the variables, like precision, accuracy, linearity, matrix effect and stability, were successfully achieved within the limits of US Food and Drug Administration guidelines. This study could provide a new protocol for the development of new analytical methods for the detection of favipiravir and its impurities.

Insights on multi-spectroscopic approaches for estimating the in vitro binding of favipiravir with adenine nucleotide.

Favipiravir (FVP) is an oral antiviral drug approved in 2021 for the treatment of COVID-19. It is a pyrazine derivative that can be integrated into anti-viral RNA products to inhibit viral replication. While, adenine is a purine nucleobase that is found in deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) to generate genetic information. For the first time, the binding mechanism between FVP and adenine was determined using different techniques, including UV-visible spectrophotometry, spectrofluorimetry, synchronous fluorescence (SF) spectroscopy, Fourier transform infrared (FTIR), fluorescence resonance energy transfer (FRET), and metal ion complexation. The fluorescence spectra indicated that FVP is bound to adenine via Van der Waals forces and hydrogen bonding through a spontaneous binding process (ΔGο < 0). The quenching mechanism was found to be static. Various temperature settings were used to investigate thermodynamic characteristics, such as binding forces, binding constants, and the number of binding sites. The reaction parameters, including the enthalpy change (ΔHο) and entropy change (ΔSο), were calculated using Van't Hoff's equation. The findings demonstrated that the adenine-FVP binding was endothermic. Furthermore, the results of the experiments revealed that some metal ions (K+, Ca+2, Co+2, Cu+2, and Al+3) might facilitate the binding interaction between FVP and adenine. Slight changes are observed in the FTIR spectra of adenine, indicating the binding interaction between adenine and FVP. This study may be useful in understanding the pharmacokinetic characteristics of FVP and how the drug binds to adenine to prevent any side effects.

In vitro antiviral activity of favipiravir and its 6- and 3-O-substituted derivatives against coronavirus: Acetylation leads to improvement of antiviral activity.

Favipiravir is currently approved for the treatment of the influenza virus and has shown encouraging results in terms of antiviral capacity in clinical studies against severe acute respiratory syndrome coronavirus 2. Favipiravir is a prodrug, where its favipiravir-ribofuranosyl-5B-triphosphate metabolite is capable of blocking RNA replication of the virus. However, the antiviral efficiency of favipiravir is limited by two factors: (i) low accumulation in plasma and rapid excretion/elimination post-administration and (ii) low conversion rate into the active metabolite. To tackle these problems, herein, we have designed new favipiravir analogues focusing on the replacement of the fluorine atom at the 6-position by halogen or hydrogen atoms and 3-O-functionalization with labile groups. The first type of functionalization seeks to increase the antiviral activity because of the better ability of the keto-tautomer as a function of the halogen, and it is hypothesized that the keto-tautomer tends to promote the formation of the ribofuranosyl-5B-triphosphate (RTP) metabolite. Meanwhile, the second type of functionalization seeks to promote lipophilicity and increase accumulation in cells. From the in vitro antiviral activity against two coronavirus models (bovine and human 229E), it was identified that the replacement did not improve the antiviral activity against both the models, which seems to be attributable to the low water solubility of these new 6-functionalized analogues. Meanwhile, with 3-O-functionalization, acetylation provided the most active compounds with higher half-maximal inhibitory concentration and selectivity than favipiravir, whereas benzylation/methanosulfonation yielded the least active compounds. In summary, acetylation is found to be a convenient functionalization to enhance the antiviral profile of favipiravir.

Tenofovir disoproxil fumarate in the treatment of COVID-19: Evaluation of 78 patients.

One of the drugs that has been suggested for the treatment of SARS-CoV-2 infection is tenofovir disoproxil (TDF). Herein, it was aimed to evaluate the outcomes of TDF receiving COVID-19 cases in terms of day 7-10 PCR negativity and day 30 survival. Patients who received TDF due to PCR-confirmed COVID-19 between 27.04.2021 and 31.12.2021 were included in our study. The primary outcome was considered to be 7-10 days of PCR negativity, while the secondary outcome was considered 30-day survival after diagnosis of COVID-19. Patients who died before completing the treatment period (7-10 days) were also considered as PCR failures. Data were analyzed both in terms of intention to treat basis and in the subgroup that survived to the end of treatment. A total of 78 patients (30 women, mean age: 61.15±18.5 years) met the inclusion criteria. In the intention to treat analysis group, one-month-mortality was 44.87% (35/78) in the overall cohort. In the end of treatment analysis group, one-month-mortality was 29.5% (18/61) in the overall cohort. Day 7-10 PCR negativity was detected in 55.7% of the overall EOT cohort. Our data suggest that TDF may be an alternative salvage treatment option in antiviral unresponsive patients. We suggest evaluating TDF in well-designed controlled trials involving treatment-naïve cases.

Evaluation of the relationship of treatment and vaccination with prognosis in patients with a diagnosis of COVID-19.

PURPOSE: Coronavirus disease 2019 (COVID-19) has affected millions of people worldwide and caused mortality. Many factors have been reported to affect the prognosis of COVID-19. In this study, we aimed to investigate the effects of drug therapy and vaccination on prognosis in patients hospitalized with a COVID-19 diagnosis. METHODS: In this single-center, cross-sectional study, data were retrospectively collected from patients receiving inpatient treatment at a university hospital with a diagnosis of COVID-19 between January 1, 2020, and April 30, 2022. The patients' demographic and clinical characteristics were recorded. The Chi-square, Cox and logistic regression was performed, P < 0.05 was considered statistically significant. RESULTS: Total 1723 patients (50.1% were men, mean age: 60.6 ± 16.90) who had not been vaccinated rate was 27.0% (> 3 doses: 45.7%). Mortality rate was 17.0%. Increasing age, male, a high Charlson Comorbidity Index (CCI), and no vaccination significantly increased mortality (P < 0.05). The mortality rate was significantly lower in the chloroquine treatment group than in the other treatment groups. Increasing age, male, and a high CCI were determined to be factors that significantly increased the length of hospital stay (LOHS). LOHS found to be significantly lower in the favipiravir or chloroquine groups compared to the remaining treatment groups (P < 0.001). Both mortality and the LOHS significantly differed according to AST, d-dimer, ferritin, and GFR. CONCLUSION: This study primarily investigated the effect of treatment and vaccination on the prognosis of COVID-19. This was determined to be prepared for another potential pandemic that may arise due to COVID-19.

Favipiravir Analogues as Inhibitors of SARS-CoV-2 RNA-Dependent RNA Polymerase, Combined Quantum Chemical Modeling, Quantitative Structure-Property Relationship, and Molecular Docking Study.

Our study was motivated by the urgent need to develop or improve antivirals for effective therapy targeting RNA viruses. We hypothesized that analogues of favipiravir (FVP), an inhibitor of RNA-dependent RNA polymerase (RdRp), could provide more effective nucleic acid recognition and binding processes while reducing side effects such as cardiotoxicity, hepatotoxicity, teratogenicity, and embryotoxicity. We proposed a set of FVP analogues together with their forms of triphosphate as new SARS-CoV-2 RdRp inhibitors. The main aim of our study was to investigate changes in the mechanism and binding capacity resulting from these modifications. Using three different approaches, QTAIM, QSPR, and MD, the differences in the reactivity, toxicity, binding efficiency, and ability to be incorporated by RdRp were assessed. Two new quantum chemical reactivity descriptors, the relative electro-donating and electro-accepting power, were defined and successfully applied. Moreover, a new quantitative method for comparing binding modes was developed based on mathematical metrics and an atypical radar plot. These methods provide deep insight into the set of desirable properties responsible for inhibiting RdRp, allowing ligands to be conveniently screened. The proposed modification of the FVP structure seems to improve its binding ability and enhance the productive mode of binding. In particular, two of the FVP analogues (the trifluoro- and cyano-) bind very strongly to the RNA template, RNA primer, cofactors, and RdRp, and thus may constitute a very good alternative to FVP.

Biochemical and histopathological evaluation of systemic and ocular toxicity of favipiravir in rats.

Purpose: Favipiravir (FAV) used against COVID-19 is an antiviral drug that causes adverse reactions, such as hyperuricaemia, liver damage, and hematopoetic toxicity. The aim of the study was to investigate the systemic and ocular side-effects of FAV in rats, for the first time.Materials and methods: A total of 18 albino male Wistar rats were used in the study. The rats were divided into 3 groups as the healthy group (HG), the group given 50 mg/kg/day favipiravir (FAV50), and the group given 200 mg/kg/d favipiravir (FAV200). These doses were given to the experimental groups for one week. At the end of the experiment histopathological examinations were performed on the conjunctiva and sclera of the eye. In addition, malondialdehyde (MDA), total glutathione (tGSH), superoxide dismutase (SOD), interleukin-1ß (IL-1ß), and tumor necrosis factor alpha (TNF-α) levels were measured in blood samples taken from rats. Results: Compared to HG, the MDA (1.37 ± 0.61 vs. 4.82 ± 1.40 µmol/mL), IL-1ß (2.52 ± 1.14 vs. 6.67 ± 1.99 pg/mL), and TNF-α levels (3.28 ± 1.42 vs. 8.53 ± 3.06 pg/mL) of the FAV200 group were higher. The levels of tGSH (7.58 ± 1.98 vs. 2.50 ± 0.98 nmol/mL) and SOD (13.63 ± 3.43 vs. 3.81 ± 1.43 U/mL) the FAV200 group were lower than the HG (p < 0.05, for all). The degree of damage to the cornea and sclera of the FAV200 group was quite high according to HG (p < 0.001). Conclusions: FAV can cause damage to rat conjunctiva and sclera by increasing oxidant stress and inflammation at high dose.

Oral Favipiravir Exposure and Pharmacodynamic Effects in Outpatient Adults with Acute Influenza.

BACKGROUND: The pharmacokinetics of oral favipiravir and the relationships of plasma concentrations to antiviral effects are incompletely studied in influenza. METHODS: Serial plasma samples were collected from adults with uncomplicated influenza who were randomized to favipiravir (1800 mg BID on day 1, 800 mg BID on days 2 to 5)(N = 827) or placebo (N = 419) in two phase 3 trials. Post hoc analyses assessed the frequency of reaching an average Cmin ≥20ug/ml, its association with antiviral efficacy, and factors associated with reduced favipiravir exposure. RESULTS: Wide inter-individual variability existed in favipiravir concentrations, and this regimen failed to reach an average Cmin >20ug/ml in 41-43% of participants. Those attaining this threshold showed greater reductions in nasopharyngeal infectious virus titers on treatment days 2 and 3 (approximately 0.3-0.4 log10TCID50/ml) and lower viral titer AUCs compared to those who did not. Those with average Cmin <20ug/ml had over 2-fold higher mean ratios of the metabolite T-705-M1 to favipiravir, consistent with greater metabolism, and were more likely to weigh >80 kg (61.5-64%). CONCLUSIONS: Higher favipiravir levels with average Cmin >20ug/ml were associated with larger antiviral effects and more rapid illness alleviation compared to placebo and to favipiravir recipients with lower average Cmin values in uncomplicated influenza.

Drug Interaction Between Favipiravir and Warfarin: A Case Series.

Introduction: Initiating favipiravir in COVID-19 patients with long-term warfarin use can lead to increased INR. However, data on the onset and duration of the increasing INR are limited. Method: We reviewed patient charts to include COVID-19 adult patients who received favipiravir for at least 5 days and used warfarin at the same dose for at least 12 weeks. Data on demographics, comorbidities, other medical characteristics, international normalized ratio (INR), and signs of bleeding were collected. Result: Eight patients, with a mean age of 70.88 ± 8.49 years old, received the standard dose of favipiravir. The mean maximum INR (4.30 ± 1.26) was statistically different from the baseline INR (P = .00029) and the change was observed within 4.38 ± 1.99 days after initiating favipiravir. Warfarin was then discontinued without favipiravir discontinuation in most patients, allowing the INR to gradually decrease within 2 to 3 days. Conclusion: Concurrent use of favipiravir and warfarin led to INR prolongation within approximately 4 days. The effect of such interaction can be acute as the prolongation occurred within 1 day in 1 of the patients.

Favipiravir in Patients With Early Mild-to-moderate Coronavirus Disease 2019 (COVID-19): A Randomized Controlled Trial.

BACKGROUND: Despite vaccination, many remain vulnerable to coronavirus disease 2019 (COVID-19) and its complications. Oral antivirals to prevent COVID-19 progression are vital. Based on perceived potency and clinical efficacy, favipiravir is widely used to treat COVID-19. Evidence from large randomized controlled trials (RCT) is lacking. METHODS: In this multicenter double-blinded placebo-controlled RCT, adults with early mild-to-moderate COVID-19 were 1:1 randomized to favipiravir or placebo. The study evaluated time to sustained clinical recovery (TT-SCR), COVID-19 progression, and cessation of viral shedding. RESULTS: Of 1187 analyzed patients across 40 centers, 83.3% were Hispanic, 89.0% unvaccinated, 70.3% severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seronegative, and 77.8% had risk factors for COVID-19 progression. The median time from symptom presentation and from positive test to randomization was 3 and 2 days, respectively. There was no difference in TT-SCR (median of 7 days for both groups; P = .80), COVID-19 progression [11 patients each (1.9% vs 1.8%); P = .96], time to undetectable virus (median = 6 days, 95% confidence interval [CI] [6-8] vs 7 days, 95% CI [6-9]), or in undetectable virus by end of therapy (73.4% vs 72.3%; P = .94). Outcomes were consistent across the analyzed sub-groups. Adverse events were observed in 13.8% and 14.8% of favipiravir-treated and placebo-treated subjects, respectively. Uric acid elevation was more frequent among favipiravir-treated subjects (19.9% vs 2.8%). CONCLUSIONS: Favipiravir was well tolerated but lacked efficacy in TT-SCR, progression to severe COVID-19, or cessation of viral shedding and should not be used to treat patients with COVID-19. (Supported by Appili Therapeutics). CLINICAL TRIALS REGISTRATION: NCT04600895.

Antiviral effect of Favipiravir against Chandipura virus in vitro and in vivo.

Chandipura virus (CHPV) is an emerging encephalitic virus with outbreak potential in a pediatric population. It causes acute encephalitis, with clinical symptoms leading to death within 48-72 h and an alarmingly high case fatality rate up to 55%-78%. Despite the high mortality rate in children, no vaccines or antivirals are currently available; thus, repurposing licensed drugs seems to be one of the attractive therapeutic approaches. Among the various options available, Favipiravir emerged as a promising candidate, and its unique characteristics and clinical efficacy have garnered significant attention and demonstrated considerable potential in the fight against viral diseases. In the current study, we have evaluated the antiviral effect of Favipiravir against CHPV by Plaque reduction assay and viral growth kinetics assay in Vero cells and in vivo effect of drug treatment against lethal viral challenge was analysed in 10-day-old CD1 mice. A dose-dependent reduction in CHPV plaque size and number was observed in Vero cells treated with Favipiravir, with an EC50 of 92.26 µM. Complete inhibition of CHPV replication was observed at 320 µM drug concentration and 50% cytotoxicity (CC50 ) at 4774 µM, indicating a high selectivity index 51.24. In vivo, studies in mice showed 100% survival with 300 mg/kg/day of Favipiravir given orally till seventh-day postinfection. The study provides evidence of the antiviral activity of Favipiravir against CHPV infection, and further clinical evaluation may alleviate the associated mortality.