Antiviral activities of multiple #antivirals against highly pathogenic avian #influenza A #H5N1 in vitro and in mice

 

ABSTRACT

In 2024, a bovine H5N1 strain was first isolated from dairy cows in Texas and confirmed to transmit cross-species to humans. Therefore, research on treatments for human infection should be accelerated. In our study, the antiviral effects of baloxavir acid (BXA), oseltamivir carboxylate (OSC), EIDD-1931 (NHC), and ribavirin (RBV) against five H5N1 strains were evaluated in vitro. Cell viability and viral replication were measured to assess the antiviral effects. The results showed that the EC50 of BXA treatment was the lowest. The BXA/NHC and BXA/OSC combination treatments showed more potent inhibitory effects than each monotherapy. The 15 mg/kg baloxavir marboxil (BXM) / 125 mg/kg molnupiravir (MNP) and the 15 mg/kg BXM / 10 mg/kg oseltamivir phosphate (OSP) were tested in BALB/c mice. The mice were inoculated with 10 times the 50% mouse lethal dose (10 MLD50) of bovine H5N1 virus. Treatments began 1-day post-infection (1 dpi) and were administered orally twice daily for 5 or 7 days. Changes in body weight, clinical signs, and survival were monitored; lung and brain tissues were collected for virological, immunological, and histological analyses. Most mice died from severe neurological symptoms. Compared with the 5-day treatment, the 7-day treatment effectively inhibited viral replication and increased survival rates to 50% in BXM, BXM/MNP, and BXM/OSP treatments. Mice treated with BXM/MNP or BXM/OSP combination therapy showed lower viral yields in the lungs than those treated with BXM alone. The results provide a reference for human treatment, and extending the 7-day combination treatment should be considered.

Source: Emerging Microbes and Infections, https://www.tandfonline.com/journals/temi20

Link: https://www.tandfonline.com/doi/full/10.1080/22221751.2026.2645843

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#SARS-CoV-2 Error Catastrophe Under #Molnupiravir: #Mutagenic Enhancement Enables Viral #Persistence with Impaired Fitness

 

Abstract

Molnupiravir induces mutations that render severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replication-competent through error catastrophe mechanisms. Previous studies showed no resistant virus emergence during prolonged molnupiravir treatment, with no resistant variants reported. However, these approaches were limited by genetic uniformity at passage initiation. To investigate viral population dynamics under enhanced genetic diversity, we employed mutagenic pre-treatment using 5-fluorouracil (5-FU) and favipiravir to generate diverse quasi-species populations before molnupiravir selection pressure. Viral populations were treated with stepwise increasing molnupiravir concentrations (10 μM ⟶ 25 μM ⟶ 40 μM) over ten serial passages. Viral detectability, plaque morphology, and mutation accumulation were analyzed using molecular and sequencing approaches. Only high-concentration favipiravir (1000 μM) pre-treatment maintained detectable viral RNA through ten passages under 40 μM molnupiravir, while favipiravir (500 μM) and 5-FU groups became undetectable after passage 6. Surviving populations formed extremely small plaques with markedly reduced replication capacity. Next-generation sequencing revealed extensive mutation accumulation across viral proteins, including polymerase proteins. Individual viable virus isolation was unsuccessful, and large-scale propagation could not be achieved. These findings demonstrate apparent survival rather than true resistance to molnupiravir, characterized by severely compromised viral fitness.

Source: 

Link: https://www.mdpi.com/1999-4915/18/2/273

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Effectiveness of #nirmatrelvir/ritonavir and #molnupiravir in reducing the #risk of short-term and long-term #cardiovascular complications of #COVID19: a target trial emulation study

 

Abstract

While treatment with nirmatrelvir/ritonavir or molnupiravir is effective in lowering the rate of severe COVID-19, the effectiveness of these antivirals in reducing the risk of cardiovascular outcomes, especially among the hospitalized population, remains largely unknown. In this study, we assessed the real-world effectiveness of nirmatrelvir/ritonavir and molnupiravir on short- and long-term cardiovascular complications of COVID-19 using a target trial emulation design. Two target trials of COVID-19 antivirals were emulated by using a territory-wide, population-based, retrospective cohort of hospitalized patients in Hong Kong. Nine cardiovascular outcomes were evaluated in both short-term (day 0–21) and long-term (day 22–365) post-SARS-CoV-2 infection. Compared with the control group, the use of nirmatrelvir/ritonavir was associated with a significantly lower one-year risk of cardiovascular mortality, composite cardiovascular complications, major adverse cardiac events, cerebrovascular disorders, dysrhythmia, ischemic heart disease, and other cardiac disorders following infection. Molnupiravir use was associated with a short-term risk reduction in cardiovascular complications, but only a marginal risk reduction in long-term cardiovascular mortality among other complications. This study demonstrated the effectiveness of nirmatrelvir/ritonavir in reducing the risks of short- and long-term cardiovascular complications following a SARS-CoV-2 infection among the hospitalized population. Our findings suggested health-related benefits of prescribing nirmatrelvir/ritonavir over molnupiravir against severe cardiovascular post-acute sequelae of COVID-19 in the long term.

Source: 

Link: https://www.nature.com/articles/s41467-025-67776-4

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#Molnupiravir clinical trial simulation suggests that #PCR underestimates #antiviral #potency against #SARS-CoV-2

 

Abstract

Molnupiravir is an antiviral medicine that induces lethal copying errors during SARS-CoV-2 RNA replication. Molnupiravir reduced hospitalization in one pivotal trial by 50% and had variable effects on reducing viral RNA levels in three separate trials. We used mathematical models to simulate these trials and closely recapitulated their virologic outcomes. Model simulations suggested lower antiviral potency against pre-Omicron SARS-CoV-2 variants than against Omicron. We estimated that in vitro assays underestimated in vivo potency by 6- to 7-fold against Omicron variants. Our model suggested that because polymerase chain reaction detects molnupiravir mutated variants, the true reduction in non-mutated viral RNA was underestimated by approximately 0.4 log10 in the two trials conducted while Omicron variants dominated. Viral area under the curve estimates differed significantly between non-mutated and mutated viral RNA. Our results reinforce past work suggesting that in vitro assays are unreliable for estimating in vivo antiviral drug potency and suggest that virologic endpoints for respiratory virus clinical trials should be catered to the drug mechanism of action.

Source: Journal of Clinical Investigation, https://www.jci.org/articles/view/192052

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#Molnupiravir inhibits #Bourbon virus #infection and disease-associated #pathology in mice

 

ABSTRACT

Bourbon virus (BRBV) is an emerging tick-borne virus that can cause severe and fatal disease in humans. BRBV is vectored via the Amblyomma americanum tick, which is widely distributed throughout the central, eastern, and southern United States. Serosurveillance studies in Missouri and North Carolina identified BRBV-neutralizing antibodies in approximately 0.6% of tested individuals. To date, no specific antiviral therapy exists. As part of an initial screen, several nucleoside analogs were tested for their ability to inhibit BRBV replication in cell culture. Among the compounds assessed, molnupiravir, an antiviral drug with oral availability and broad spectrum antiviral activity against RNA viruses, showed antiviral activity against BRBV production in vitro. In vivo, pre-exposure administration of molnupiravir protected susceptible type I interferon receptor knockout (Ifnar1-/-) mice against lethal BRBV infection. The protection by molnupiravir was associated with lower virus burden in mouse tissues, improvement of T-cell (CD4+, CD8+) and B-cell (follicular) profiles in the spleen, improvement of severe thrombocytopenia, and reduced pathology in the spleen and liver of BRBV-infected mice. Finally, therapeutic administration of molnupiravir starting 24 or 48 hours after infection ameliorated weight loss, clinical signs of disease, and lethality associated with BRBV infection. Overall, our experiments suggest that molnupiravir is a potential antiviral therapy for evaluation in humans with BRBV infections.

IMPORTANCE

Bourbon virus (BRBV) is an emerging tick-borne pathogen that can cause severe and fatal illness in humans. Currently, there are no approved antiviral therapies or vaccines against this disease. In this study, we evaluated the efficacy of molnupiravir, a broad-spectrum antiviral drug that is approved in the United States for other RNA viruses, using a mouse model of lethal BRBV disease. Molnupiravir significantly inhibited virus replication, improved survival rates, and suppressed clinical signs of disease, including thrombocytopenia and liver and spleen pathology. These findings support further investigation of molnupiravir as a potential therapeutic candidate for treating BRBV infections in humans.

Source: Journal of Virology, https://journals.asm.org/doi/full/10.1128/jvi.00740-25?af=R

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#Placental transfer of #medications to treat #COVID19, #molnupiravir, #favipiravir and #nirmatrelvir/ritonavir, in the ex vivo human cotyledon model

 

Abstract

Objectives

There have been few studies in pregnant women of medications that are used to reduce severe complications from COVID-19 infection. Currently, nirmatrelvir/ritonavir (Paxlovid) is recommended by the National Institutes for Health to treat non-hospitalized pregnant patients with mild-to-moderate COVID-19 illness. The aim of this study was to determine the transplacental passage of molnupiravir, nirmatrelvir/ritonavir and favipiravir utilizing an ex vivo placental perfusion model.

Methods

Human placental cotyledons were continuously perfused in a double open circuit. The study molecules and antipyrine, a marker of placental viability, were dissolved in the maternal solution. The experiment was conducted over 90 minutes, and every 5 minutes, samples of the maternal solution and fetal exchange solutions were collected for analysis. We calculated the concentrations of study molecules, fetal transfer ratios and the clearance indexes to determine placental transfer.

Results

Of 18 placentas analysed, 14 were validated by antipyrine transfer. Nirmatrelvir alone had low placental transfer, with a fetal transfer ratio of 0.025. Its placenta transfer increased in the presence of ritonavir, with a fetal transfer ratio of 0.06. The molnupiravir metabolite, β-D-N-4-hydroxycytidine (EIDD 1931), showed low placental transfer, with an average fetal transfer ratio of 0.04. By contrast, favipiravir crossed the placenta with an average fetal transfer ratio of 0.425.

Conclusions

Placental transfer was high for the nucleoside analogue favipiravir, while it was low for molnupiravir and low for the protease inhibitor nirmatrelvir but increased by ritonavir. Clinical data are required to confirm the placental transfer and determine the safety of COVID antivirals in pregnancy.

Source: Journal of Antimicrobial Chemotherapy, https://academic.oup.com/jac/advance-article-abstract/doi/10.1093/jac/dkaf302/8245204?redirectedFrom=fulltext

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The combinatorial activities of #oseltamivir and #molnupiravir against #influenza virus infections in vitro and in vivo

Highlights

• Mol shows greater antiviral effects against IAV and IBV in cell cultures.

• Mol and Ose together showed a synergistic effect against IAV.

• In mice, Mol alone or with Ose reduced lung injury and viral load.

Abstract

Oseltamivir, a neuraminidase inhibitor, is widely used in the clinic for treating influenza virus infections. However, suboptimal efficacy and risk of drug resistance development remain major challenges. Molnupiravir, a ribonucleoside analog, was originally developed to treat influenza, but was repurposed and first approved for treating COVID-19 in 2021. Considering their complementary mode-of-actions, this study aimed to investigate the combinatorial activities of oseltamivir and molnupiravir against influenza virus infections. In cell culture models, we found that β-d-N4-hydroxycytidine (NHC), the active form of molnupiravir, exerted more potent antiviral activities against influenza A and B viruses, when compared to oseltamivir treatment. Combination of NHC with oseltamivir exhibited a synergistic antiviral effect against the influenza A/Puerto Rico/8/34 H1N1 strain, but not the influenza B/Washington/02/2019 strain. In a mouse model infected with the PR/8 virus strain, treatment with molnupiravir alone or in combination with oseltamivir effectively attenuated lung injury and reduced viral load in the tissue. Taken together, molnupiravir can be explored in combination with oseltamivir to treat influenza, especially for patients infected with the oseltamivir-resistant strains, whereas further research is warranted.

Source: Virology, https://www.sciencedirect.com/science/article/abs/pii/S0042682225002557?via%3Dihub

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#SARS-CoV-2 #rebound and post-acute #mortality and hospitalization among patients admitted with #COVID19: cohort study

Abstract

Recent investigations have demonstrated a relationship between the persistence of SARS-CoV-2 and post-COVID-19 conditions. Building upon a potential connection between SARS-CoV-2 persistence and early virologic rebound, we examine the association of early virologic rebound with post-acute mortality and hospitalization due to post-acute sequelae among hospitalized patients with COVID-19 in Hong Kong. Our study includes 13,859, 3959, and 4502 patients in the all-patient, nirmatrelvir/ritonavir, and molnupiravir group, respectively. Results show that patients who experienced virologic rebound exhibited a significantly higher risk of post-acute mortality (hazard ratio [HR], 1.52; 95% confidence interval [CI], 1.36–1.70) with a risk difference [RD] of 7.19%, compared with patients without virologic rebound. A similar increase in the risk of post-acute mortality is also observed in nirmatrelvir/ritonavir-treated patients (HR, 1.78; 95% CI, 1.41–2.25; RD, 12.55%) and molnupiravir-treated patients (HR, 1.47; 95% CI, 1.18–1.82; RD, 4.90%). The virologic rebound may thus serve as an early marker for post-COVID-19 condition, enabling healthcare officials to monitor and provide timely intervention for long COVID.

Source: Nature Communications, https://www.nature.com/articles/s41467-025-61737-7

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#Molnupiravir or #nirmatrelvir–ritonavir plus usual care vs usual care alone in patients admitted to #hospital with #COVID19 (RECOVERY)...

Summary

Background

Molnupiravir and nirmatrelvir–ritonavir are oral antivirals that have shown efficacy in preventing disease progression in outpatients with COVID-19. We aimed to evaluate these treatments for patients hospitalised with COVID-19 pneumonia, for whom data on these antivirals are scarce.

Methods

The RECOVERY trial is a randomised, controlled, open-label, adaptive platform trial testing treatments for COVID-19. In this study we report the molnupiravir and nirmatrelvir–ritonavir comparisons from the RECOVERY trial. In each comparison, participants aged 18 years and older were randomly allocated (1:1) to the relevant antiviral (5 days of molnupiravir 800 mg twice daily or 300 mg nirmatrelvir and 100 mg ritonavir twice daily) in addition to usual care, or to usual care alone. The molnupiravir comparison was conducted at 75 hospitals in the UK, two in Nepal, and two in Indonesia; the nirmatrelvir–ritonavir comparison was conducted at 32 hospitals in the UK. Participants could take part in both comparisons. The primary outcome was 28-day mortality, and secondary outcomes were time to discharge alive from hospital and progression to invasive ventilation or death. Analysis was by intention to treat. Both comparisons were stopped because of low recruitment. This study is registered with ISRCTN, 50189673, and ClinicalTrials.gov, NCT04381936.

Findings

From Jan 24, 2022, to May 24, 2023, 923 participants were recruited to the molnupiravir comparison (445 allocated to molnupiravir and 478 to usual care), and from March 31, 2022, to May 24, 2023, 137 participants were recruited to the nirmatrelvir–ritonavir comparison (68 allocated to nirmatrelvir–ritonavir and 69 to usual care). More than three-quarters of participants were vaccinated and had antispike antibodies at randomisation, and more than two-thirds were receiving other SARS-CoV-2 antivirals. In the molnupiravir comparison, 74 (17%) participants allocated to molnupiravir and 79 (17%) allocated to usual care died within 28 days (hazard ratio [HR] 0·93 [95% CI 0·68–1·28], p=0·66). In the nirmatrelvir–ritonavir comparison, 13 (19%) participants allocated to nirmatrelvir–ritonavir and 13 (19%) allocated to usual care died within 28 days (HR 1·02 [0·47–2·23], p=0·96). In neither comparison was there evidence of any difference in the duration of hospitalisation or the proportion of participants progressing to invasive ventilation or death.

Interpretation

Adding molnupiravir or nirmatrelvir–ritonavir to usual care was not associated with improvements in clinical outcomes. However, low recruitment meant a clinically meaningful benefit of treatment could not be ruled out, particularly for nirmatrelvir–ritonavir.

Source: Lancet Infectious Diseases, https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(25)00093-3/fulltext?rss=yes

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