Ribavirin: a clinical overview

Repurposing existing drugs for the treatment ofCOVID-19/SARS-CoV-2: A review of pharmacological effects and mechanism of action

Following the coronavirus disease-2019 outbreak caused by severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), there is an ongoing need to seek drugs that target COVID-19. First off, novel drugs have a long development cycle, high investment cost, and are high risk. Second, novel drugs must be evaluated for activity, efficacy, safety, and metabolic performance, contributing to the development cycle, investment cost, and risk. We searched the Cochrane COVID-19 Study Register (including PubMed, Embase, CENTRAL, ClinicalTrials.gov, WHO ICTRP, and medRxiv), Web of Science (Science Citation Index, Emerging Citation Index), and WHO COVID-19 Coronaviral Disease Global Literature to identify completed and ongoing studies as of February 20, 2024. We evaluated the pharmacological effects, in vivo and in vitro data of the 16 candidates in the paper. The difficulty of studying these candidates in clinical trials involving COVID-19 patients, dosage of repurposed drugs, etc. is discussed in detail. Ultimately, Metformin is more suitable for prophylactic administration or mildly ill patients; the combination of Oseltamivir, Tamoxifen, and Dexamethasone is suitable for moderately and severely ill patients; and more clinical trials are needed for Azvudine, Ribavirin, Colchicine, and Cepharanthine to demonstrate efficacy.

Identification of 3, 4-dihydroxy complexes as potential antiviral via DFT, molecular docking, molecular dynamics and MM/PBSA against rabies and dengue receptors

The quest to identify antiviral drug candidates for dengue and rabies viral diseases is a great challenge for the researchers. While different research is being conducted on the repurposed drugs against these two viruses, no drug compound has gained success in treating them. Therefore, in this study, 3, 4-dihydroxy complexes have been virtually designed to investigate their antiviral properties and analyze their efficiency in interaction with the concerned viral diseases. DFT calculations are carried out to study the electronic and thermodynamic properties to understand the stability and reactivity of the reported compounds. These compounds were subjected to molecular docking studies to understand the binding interactions with NS5 Dengue virus mRNA 2'-O-methyltransferase and phosphoprotein C-terminal domain of Rabies virus. MD simulation, hydrogen bond analysis, and MM/PBSA were performed at 100 ns to support the obtained docking results.Communicated by Ramaswamy H. Sarma.

Medicinal chemistry strategies toward broad-spectrum antiviral agents to prevent next pandemics

The pandemic and tremendous impact of severe acute respiratory syndrome coronavirus 2 alert us, despite great achievements in prevention and control of infectious diseases, we still lack universal and powerful antiviral strategies to rapidly respond to the potential threat of serious infectious disease. Various highly contagious and pathogenic viruses, as well as other unknown viruses may appear or reappear in human society at any time, causing a catastrophic epidemic. Developing broad-spectrum antiviral drugs with high security and efficiency is of great significance for timely meeting public health emergency and protecting the lives and health of the people. Hence, in this review, we summarized diverse broad-spectrum antiviral targets and corresponding agents from a medicinal chemistry prospective, compared the pharmacological advantages and disadvantages of different targets, listed representative agents, showed their structures, pharmacodynamics and pharmacokinetics characteristics, and conducted a critical discussion on their development potential, in the hope of providing up-to-date guidance for the development of broad-spectrum antivirals and perspectives for applications of antiviral therapy.

In Silico Identification and In Vitro Validation of Repurposed Compounds Targeting the RSV Polymerase

Respiratory Syncytial Virus (RSV) is the top cause of infant hospitalization globally, with no effective treatments available. Researchers have sought small molecules to target the RNA-dependent RNA Polymerase (RdRP) of RSV, which is essential for replication and transcription. Based on the cryo-EM structure of the RSV polymerase, in silico computational analysis including molecular docking and the protein-ligand simulation of a database, including 6554 molecules, is currently undergoing phases 1-4 of clinical trials and has resulted in the top ten repurposed compound candidates against the RSV polymerase, including Micafungin, Totrombopag, and Verubecestat. We performed the same procedure to evaluate 18 small molecules from previous studies and chose the top four compounds for comparison. Among the top identified repurposed compounds, Micafungin, an antifungal medication, showed significant inhibition and binding affinity improvements over current inhibitors such as ALS-8112 and Ribavirin. We also validated Micafungin's inhibition of the RSV RdRP using an in vitro transcription assay. These findings contribute to RSV drug development and hold promise for broad-spectrum antivirals targeting the non-segmented negative-sense (NNS) RNA viral polymerases, including those of rabies (RABV) and Ebola (EBOV).

Antiviral Efficacy of Ribavirin and Favipiravir against Hantaan Virus

Ecological changes, population movements and increasing urbanization promote the expansion of hantaviruses, placing humans at high risk of virus transmission and consequent diseases. The currently limited therapeutic options make the development of antiviral strategies an urgent need. Ribavirin is the only antiviral used currently to treat hemorrhagic fever with renal syndrome (HFRS) caused by Hantaan virus (HTNV), even though severe side effects are associated with this drug. We therefore investigated the antiviral activity of favipiravir, a new antiviral agent against RNA viruses. Both ribavirin and favipiravir demonstrated similar potent antiviral activity on HTNV infection. When combined, the efficacy of ribavirin is enhanced through the addition of low dose favipiravir, highlighting the possibility to provide better treatment than is currently available.

SARS-CoV-2 RNA-dependent RNA polymerase as a therapeutic target for COVID-19

Introduction: The current SARS-CoV-2 pandemic urgently demands for both prevention and treatment strategies. RNA-dependent RNA-polymerase (RdRp), which has no counterpart in human cells, is an excellent target for drug development. Given the time-consuming process of drug development, repurposing drugs approved for other indications or at least successfully tested in terms of safety and tolerability, is an attractive strategy to rapidly provide an effective medication for severe COVID-19 cases.Areas covered: The currently available data and upcominSg studies on RdRp which can be repurposed to halt SARS-CoV-2 replication, are reviewed.Expert opinion: Drug repurposing and design of novel compounds are proceeding in parallel to provide a quick response and new specific drugs, respectively. Notably, the proofreading SARS-CoV-2 exonuclease activity could limit the potential for drugs designed as immediate chain terminators and favor the development of compounds acting through delayed termination. While vaccination is awaited to curb the SARS-CoV-2 epidemic, even partially effective drugs from repurposing strategies can be of help to treat severe cases of disease. Considering the high conservation of RdRp among coronaviruses, an improved knowledge of its activity in vitro can provide useful information for drug development or drug repurposing to combat SARS-CoV-2 as well as future pandemics.

The situation of small molecules targeting key proteins to combat SARS-CoV-2: Synthesis, metabolic pathway, mechanism of action, and potential therapeutic applications

Due to the global epidemic and high mortality of 2019 coronavirus disease (COVID-19), there is an immediate need to discover drugs that can help before a vaccine becomes available. Given that the process of producing new drugs is so long, the strategy of repurposing existing drugs is one of the promising options for the urgent treatment of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes COVID-19 disease. Although FDA has approved Remdesivir for the use in hospitalized adults and pediatric patients suffering from COVID-19, no fully effective and reliable drug has been yet identified worldwide to treat COVID-19 specifically. Thus, scientists are still trying to find antivirals specific to COVID-19. This work reviews the chemical structure, metabolic pathway, mechanism of action of existing drugs with potential therapeutic applications for COVID-19. Further, we summarized the molecular docking stimulation of the medications related to key protein targets. These already drugs could be developed for further clinical trials to supply suitable therapeutic options for patients suffering from COVID-19.

Assessment of the efficacy and safety of Ribavirin in treatment of coronavirus-related pneumonia (SARS, MERS and COVID-19): A protocol for systematic review and meta-analysis

BACKGROUND

The new coronavirus-related pneumonia is causing a global pandemic without specific antiviral drug. Ribavirin has activity against extensive RNA and DNA viruses. We plan to systematically review the use of ribavirin in patients with coronavirus-related pneumonia and meta-analyze the data with updated studies.

METHODS

EMBASE, PubMed, Cochrane Library, and China National Knowledge Infrastructure will be searched from 2002 to June 2021 without language restriction to identify randomized controlled trials. Subjects consist of patients with coronavirus-related pneumonia. Ribavirin of any dose or route will be compared with the control group of other medication, placebo, or no medication. The primary outcome is the hospital mortality. The secondary outcome includes the hospital length of stay, ventilator-free days in 28 days, median time from start of study treatment to negative nasopharyngeal swab, and adverse events. The Mantel-Haenszel method will be used for analysis of dichotomous data and the risk ratios will be reported with 95% confidence interval; the inverse-variance method will be used for continuous data and the mean differences will be reported. Sensitivity and subgroup analyses will be further performed. The funnel plots or Egger test will be used for detection of publication bias. The GRADE methodology will be used for summarizing the quality of evidence. The trial sequential analysis will be conducted to test whether the current meta-analysis is conclusive.

RESULTS

The efficacy and safety of ribavirin for treatment of coronavirus-related pneumonia will be systematically reviewed and summarized. The forthcoming results of the ongoing studies focusing on ribavirin in patients with the 2019 noel coronavirus disease will also be included.

CONCLUSION

The relevant studies will be summarized and advanced evidence will be provided.

PROSPERO REGISTRATION NUMBER

CRD42020178900.

The emerging tick-borne Crimean-Congo haemorrhagic fever virus: A narrative review

Crimean-Congo Haemorrhagic Fever (CCHF) is an increasingly relevant viral zoonosis caused by the negative-sense single-stranded (ss) RNA Crimean-Congo Haemorrhagic Fever Orthonairovirus (CCHFV) (Nairoviridae family, Bunyavirales order). The viral genome is divided into three segments (L-M-S) of distinct size and functions. The infection is generally mediated by a tick vector, in particular belonging to the Hyalomma genus, and the transmission follows a tick-vertebrate-tick ecologic cycle, with asymptomatic infected animals functioning as reservoirs and amplifiers for CCHFV. Human hosts could be infected primarily through infected ticks or by contact with infected hosts or their body fluids and tissues, also in a nosocomial way and in occupational contexts. Infected symptomatic patients generally manifest a nonspecific illness, which progresses across four stages, with possibly lethal outcomes. Disease outbreaks show a widespread geographic diffusion and a highly variable mortality rate, dramatically peaking in untreated patients. The lack of an adequate animal model and the elevated virus biological risk (only manageable under biosafety level 4 conditions) represent strongly limiting factors for a better characterization of the disease and for the development of specific therapies and vaccines. The present review discusses updated information on CCHFV-related disease, including details about the virus (taxonomy, structure, life cycle, transmission modalities) and considering CCHF pathogenesis, epidemiology and current strategies (diagnostic, therapeutic and preventive).

Measles Resurgence and Drug Development

Measles caused an estimated minimum of one million fatalities annually before vaccination. Outstanding progress towards controlling the virus has been made since the measles vaccine was introduced, but reduction of measles case-fatalities has stalled at around 100,000 annually for the last decade and a 2019 resurgence in several geographical regions threatens some of these past accomplishments. Whereas measles eradication through vaccination is feasible, a potentially open-ended endgame of elimination may loom. Other than doubling-down on existing approaches, is it worthwhile to augment vaccination efforts with antiviral therapeutics to solve the conundrum? This question is hypothetical at present, since no drugs have yet been approved specifically for the treatment of measles, or infection by any other pathogen of the paramyxovirus family. This article will consider obstacles that have hampered anti-measles and anti-paramyxovirus drug development, discuss MeV-specific challenges of clinical testing, and define drug properties suitable to address some of these problems.

In vitro antiviral activity of ribavirin against severe fever with thrombocytopenia syndrome virus

BACKGROUND/AIMS

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by severe fever with thrombocytopenia syndrome virus (SFTSV), a novel bunyavirus. As yet, there is no effective antiviral therapy for SFTS. Ribavirin is a broad-spectrum antiviral agent, which has been tried for treatment of SFTS. In this study, antiviral activity of ribavirin against SFTSV has been investigated.

METHODS

Vero cell-grown SFTSV strain Gangwon/Korea/2012 was treated with ribavirin at various concentrations. Antiviral activity of ribavirin was evaluated by inhibition of the SFTSV cytopathic effect in Vero cells and quantification of viral RNA load in culture supernatant using one-step real-time reverse transcription polymerase chain reaction. Cytotoxicity of ribavirin was determined by a tetrazolium-based colorimetric method.

RESULTS

Ribavirin reduced SFTSV titers in a dose-dependent manner, with a half-maximal inhibitory concentration ranged from 3.69 to 8.72 μg/mL. Cytopathic effects were reduced as ribavirin concentration increased. No significant cytotoxicity was detected at ribavirin concentrations of ≤ 31.3 μg/mL.

CONCLUSIONS

Ribavirin exhibited inhibitory activity against SFTSV replication in vitro, which suggests that ribavirin can be used as a potential antiviral agent for SFTS.

Hematological adverse effects and pharmacokinetics of ribavirin in pigs following intramuscular administration

Ribavirin (RBV) is a synthetic guanosine analog that is used as a drug against various viral diseases in humans. The in vitro antiviral effects of ribavirin against porcine viruses were demonstrated in several studies. The purposes of this study were to evaluate the adverse effects and pharmacokinetics of ribavirin following its intramuscular (IM) injection in pigs. Ribavirin was formulated as a double-oil emulsion (RBV-DOE) and gel (RBV-Gel), which were injected into the pigs as single-dose IM injections. After injection of RBV, all of the pigs were monitored. The collected serum and whole blood samples were analyzed by liquid chromatography-tandem mass spectrometry and complete blood count analysis, respectively. All of the ribavirin-treated pigs showed significant decreases in body weight compared to the control groups. Severe clinical signs including dyspnea, anorexia, weakness, and depression were present in ribavirin-treated pigs until 5 days postinjection (dpi). The ribavirin-treated groups showed significant decrease in the number of red blood cells and hemoglobin concentration until 8 dpi. The mean half-life of the RBV-DOE and RBV-Gel was 27.949 ± 2.783 h and 37.374 ± 3.502 h, respectively. The mean peak serum concentration (C_max ) and area under the serum concentration-time curve from time zero to infinity (AUC_inf ) of RBV-DOE were 8340.000 ± 2562.577 ng/mL and 16 0095.430 ± 61 253.400 h·ng/mL, respectively. The C_max and AUC_inf of RBV-Gel were 15 300.000 ± 3764.306 ng/mL and 207526.260 ± 63656.390 h·ng/mL, respectively. The results of this study provided the index of side effect and pharmacokinetics of ribavirin in pigs, which should be considered before clinical application.

A Novel Endonuclease Inhibitor Exhibits Broad-Spectrum Anti-Influenza Virus Activity In Vitro

Antiviral drugs are important in preventing and controlling influenza, particularly when vaccines are ineffective or unavailable. A single class of antiviral drugs, the neuraminidase inhibitors (NAIs), is recommended for treating influenza. The limited therapeutic options and the potential risk of antiviral resistance are driving the search for additional small-molecule inhibitors that act on influenza virus proteins. The acid polymerase (PA) of influenza viruses is a promising target for new antivirals because of its essential role in initiating virus transcription. Here, we characterized a novel compound, RO-7, identified as a putative PA endonuclease inhibitor. RO-7 was effective when added before the cessation of genome replication, reduced polymerase activity in cell-free systems, and decreased relative amounts of viral mRNA and genomic RNA during influenza virus infection. RO-7 specifically inhibited the ability of the PA endonuclease domain to cleave a nucleic acid substrate. RO-7 also inhibited influenza A viruses (seasonal and 2009 pandemic H1N1 and seasonal H3N2) and B viruses (Yamagata and Victoria lineages), zoonotic viruses (H5N1, H7N9, and H9N2), and NAI-resistant variants in plaque reduction, yield reduction, and cell viability assays in Madin-Darby canine kidney (MDCK) cells with nanomolar to submicromolar 50% effective concentrations (EC50s), low toxicity, and favorable selective indices. RO-7 also inhibited influenza virus replication in primary normal human bronchial epithelial cells. Overall, RO-7 exhibits broad-spectrum activity against influenza A and B viruses in multiple in vitro assays, supporting its further characterization and development as a potential antiviral agent for treating influenza.

Combination effects of ribavirin and interferons on severe fever with thrombocytopenia syndrome virus infection

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an acute infectious disease caused by SFTS virus and characterized by a high case fatality rate. Currently, there is no effective therapy for the disease. While the administration of ribavirin does not improve the case fatality rate or viral load in patient blood, it can inhibit viral infection in vitro.

Methods

Vero cells were pre-treated with interferons (IFNs) α, β, and γ alone and in combination with ribavirin drugs and inoculated with SFTS virus. Three days later, supernatants were harvested and subjected to virus titration. An unpaired t-test was used for statistical analysis of the drugs’ effects.

Results

While the effects of IFNγ at high concentrations were slightly weaker than those of the other IFNs, all IFNs showed dose-dependent inhibitory effects. The combined usage of IFNs with ribavirin at 90 % effective concentrations showed large inhibitory effects, with over a 3 log₁₀ reduction in viral titers.

Conclusions

The combined usage of one of type-I/II IFNs with ribavirin drastically reduced SFTS virus infection and therefore may be useful in the treatment of SFTS.

Effects of ribavirin on severe fever with thrombocytopenia syndrome virus in vitro

Severe fever with thrombocytopenia syndrome (SFTS) is a disease with a high case fatality rate that is caused by infection with the recently identified tick-borne SFTS virus (SFTSV), for which there are no specific countermeasures. We examined the effects of ribavirin and mizoribine, which are nucleoside analogue drugs with broad antiviral activities, on SFTSV proliferation in vitro. When 3 cell lines were treated with these drugs before and during infection with a Chinese SFTSV strain, the 99% effective concentrations (EC99) of ribavirin were 19-64 μg/ml (78-262 μM); in contrast, the EC99 of mizoribine was >500 μg/ml (1,929 μM). Similar levels of inhibitory effects of ribavirin were observed with 4 Japanese SFTSV strains. However, when Vero cells were treated with ribavirin 3 days after inoculation, the inhibitory effect was dramatically decreased, indicating that ribavirin did not effectively reduce virus production in pre-infected cells. These results suggest that ribavirin could be used as post-exposure prophylaxis for the prevention of SFTS.

Exploring the influence of renal dysfunction on the pharmacokinetics of ribavirin after oral and intravenous dosing

Although ribavirin is minimally cleared by renal elimination, its pharmacokinetics are substantially altered in patients with chronic renal impairment. This open-label study assessed the pharmacokinetics of single 400-mg oral and intravenous (IV) doses of ribavirin in two healthy volunteers and 12 patients with varying degrees of chronic renal impairment. Blood and urine samples were collected pre-dose and up to 168 h post-dose for pharmacokinetic analyses. Ribavirin area under the plasma concentration-time curve from time zero to time of final quantifiable sample and maximum plasma concentration values were increased, and total plasma clearance (CL), renal clearance (CLr), non-renal clearance (CLnr), volume of distribution at steady state (Vdss), and amount excreted values were reduced in patients with renal dysfunction compared with those who had normal renal function. Following IV administration, mean CLr was 54%, 23%, and 10% in patients with mild, moderate, and severe renal dysfunction, respectively, relative to control subjects, and was 56%, 28%, and 9% of control values after oral dosing. After IV dosing, mean CLnr was 94%, 76%, and 75% of control values in patients with mild, moderate, and severe renal dysfunction, respectively, and was 54%, 48%, and 27% of control values after oral dosing. Mean oral bioavailability of ribavirin was 35%, 60%, 57%, and 71% in control subjects and patients with mild, moderate, and severe renal dysfunction, respectively. These data indicate that there are multiple mechanisms (increased oral bioavailability, reduced CLr and CLnr, reduced Vd) contributing to altered ribavirin pharmacokinetics in chronic renal impairment.

Synergizing vaccinations with therapeutics for measles eradication

INTRODUCTION

The measles virus is a major human pathogen responsible for approximately 150,000 deaths annually. The disease is vaccine preventable and eradication of the virus is considered feasible, in principle. However, a herd immunity exceeding 95% is required to prevent sporadic viral outbreaks in a population. Declining disease prevalence, combined with public anxiety over the vaccination's safety, has led to increased vaccine refusal, especially in Europe. This has led to the resurgence of measles in some areas.

AREAS COVERED

This article discusses whether synergizing effective measles therapeutics with the measles vaccination could contribute to finally eradicating measles. The authors identify key elements in a desirable drug profile and review current disease management strategies and the state of experimental inhibitor candidates. The authors also evaluate the risk associated with viral escape from inhibition, and consider the potential of measles therapeutics in the management of persistent central nervous system (CNS) viral infection. Finally, the authors contemplate the possible impact of therapeutics in controlling the threat imposed by closely related zoonotic pathogens of the same genus as measles.

EXPERT OPINION

Efficacious therapeutics used for post-exposure prophylaxis of high-risk social contacts of confirmed index cases may aid measles eradication by closing herd immunity gaps; this is due to vaccine refusal or failure in populations with overall good vaccination coverage. The envisioned primarily prophylactic application of measles therapeutics to a predominantly pediatric and/or adolescent population, dictates the drug profile. It also has to be safe and efficacious, orally available, shelf-stable at ambient temperature and amenable to cost-effective manufacturing.

Comparative study to evaluate the anti-viral efficacy of Glycyrrhiza glabra extract and ribavirin against the Newcastle disease virus

BACKGROUND

The Newcastle disease represents as one of the most infectious viral disease, which afflicts almost every species of the birds. The causative agent of the disease is a single-stranded RNA virus with rapid replication capability.

OBJECTIVE

This study was performed to evaluate the comparative anti-viral efficacy and toxicity of Glycyrrhiza glabra aqueous extract and ribavirin against the Newcastle disease virus.

MATERIALS AND METHODS

The embryonated eggs were divided into six groups (A, B, C, D, E and F). Groups A, B, C, and D were further subdivided into three subgroups. The virus was identified by hemagglutination inhibition test. Spot hemagglutination test and viability of embryos were also evaluated. Three different concentrations i-e., 30 mg/100 ml, 60 mg/100 ml, and 120 mg/100 ml of the Glycyrrhiza aqueous extract and 10 μg/ml, 20 μg/ml, and 40 μg/ml ribavirin in deionized water were evaluated for their toxicity and anti-viral activity in the embryonated eggs.

RESULTS

60 mg/100 ml concentration of Glycyrrhiza extract did not produce any toxicity in the embryonated eggs and showed anti-viral activity against the virus. Similarly, 20 μg/ml ribavirin was non-toxic in the embryonated eggs and contained anti-viral activity.

CONCLUSION

It may conclude from the presented study that 60 mg/100 ml Glycyrrhiza extract inhibits replication of Newcastle disease virus and is non-toxic in the embryonated eggs. So, Glycyrrhiza glabra extract may be further evaluated in future to determine the potentially active compounds for their anti-viral activity against Newcastle disease virus. Furthermore, the mechanism of action of these active phytochemicals as an antiviral agent would be helpful to elucidate the pathogenesis of the disease.

Ribavirin protects Syrian hamsters against lethal hantavirus pulmonary syndrome--after intranasal exposure to Andes virus

Andes virus, ANDV, harbored by wild rodents, causes the highly lethal hantavirus pulmonary syndrome (HPS) upon transmission to humans resulting in death in 30% to 50% of the cases. As there is no treatment for this disease, we systematically tested the efficacy of ribavirin in vitro and in an animal model. In vitro assays confirmed antiviral activity and determined that the most effective doses were 40 µg/mL and above. We tested three different concentrations of ribavirin for their capability to prevent HPS in the ANDV hamster model following an intranasal challenge. While the highest level of ribavirin (200 mg/kg) was toxic to the hamster, both the middle (100 mg/kg) and the lowest concentration (50 mg/kg) prevented HPS in hamsters without toxicity. Specifically, 8 of 8 hamsters survived intranasal challenge for both of those groups whereas 7 of 8 PBS control-treated animals developed lethal HPS. Further, we report that administration of ribavirin at 50 mg/kg/day starting on days 6, 8, 10, or 12 post-infection resulted in significant protection against HPS in all groups. Administration of ribavirin at 14 days post-infection also provided a significant level of protection against lethal HPS. These data provide in vivo evidence supporting the potential use of ribavirin as a post-exposure treatment to prevent HPS after exposure by the respiratory route.

Review of the literature and proposed guidelines for the use of oral ribavirin as postexposure prophylaxis for Lassa fever

Lassa fever is an acute viral hemorrhagic illness; the virus is endemic in West Africa and also of concern with regard to bioterrorism. Transmission of Lassa virus between humans may occur through direct contact with infected blood or bodily secretions. Oral administration of the antiviral drug ribavirin is often considered for postexposure prophylaxis, but no systematically collected data or uniform guidelines exist for this indication. Furthermore, the relatively low secondary attack rates for Lassa fever, the restriction of the area of endemicity to West Africa, and the infrequency of high-risk exposures make it unlikely that controlled prospective efficacy trials will ever be possible. Recommendations for postexposure use of ribavirin can therefore be made only on the basis of a thorough understanding and logical extrapolation of existing data. Here, we review the pertinent issues and propose guidelines based on extensive review of the literature, as well as our experience in this field. We recommend oral ribavirin postexposure prophylaxis for Lassa fever exclusively for definitive high-risk exposures. These guidelines may also serve for exposure to other hemorrhagic fever viruses susceptible to ribavirin.

Lethal mutagenesis in a structured environment

We analyze how lethal mutagenesis operates in a compartmentalized host. We assume that different compartments receive different amounts of mutagen and that virions can migrate among compartments. We address two main questions: (1) To what extent can refugia, i.e., compartments that receive little mutagen, prevent extinction? (2) Does migration among compartments limit the effectiveness of refugia? We find that if there is little migration, extinction has to be achieved separately in all compartments. In this case, the total dose of mutagen administered to the host needs to be so high that the mutagen is effective even in the refugia. By contrast, if migration is extensive, then lethal mutagenesis is effective as long as the average growth in all compartments is reduced to below replacement levels. The effectiveness of migration is governed by the ratio of virion replication and death rates, R(0). The smaller R(0), the less migration is necessary to neutralize refugia and the less mutagen is necessary to achieve extinction at high migration rates.

Ribavirin: current role in the optimal clinical management of chronic hepatitis C

Ribavirin in combination with peginterferon alfa shows strong clinical efficacy against chronic hepatitis C, and is now established as the standard of care. However, the precise role of ribavirin is still being defined, suggesting that optimal ribavirin dose should be maintained over the whole treatment period. Ribavirin dosage varies by bodyweight for genotype 1 disease (1000mg/day in patients <or =75kg and 1200mg/day in patients >75kg), whereas 800mg/day is sufficient to ensure optimal response in all genotype 2/3 patients. Similarly, genotype 1 patients benefit from 48 weeks of therapy, while 24 weeks is sufficient for genotype 2/3 disease. Recent data suggest treatment success is dependent on cumulative ribavirin exposure, as patients who receive <60% of the planned dose have lower response rates, regardless of whether reductions are from temporary interruptions or premature cessation of therapy. All patients should be monitored for hemolytic anemia, as early diagnosis allows management through small dose reductions and stepwise return to the target dose, maximizing cumulative exposure. Despite these recent advances in our knowledge, many questions remain, such as whether the role of ribavirin will change or even be eliminated as new therapies are developed.

What future for ribavirin?

The optimal therapy for patients with the chronic hepatitis C virus (HCV) is a combination of peginterferon and ribavirin. Treating HCV without ribavirin or prematurely discontinuing, frequently missing doses of ribavirin is associated with a significant decline in virological response, and an increase in both breakthrough viraemia and relapse. The major limitation of ribavirin is adverse events, the most common of which is haemolytic anaemia. Haemolysis is modest when ribavirin is utilized as monotherapy, but is significantly increased when combined with interferon or peginterferon. For these reasons, attempts to replace ribavirin with a less toxic alternative have been advanced. Unfortunately, even when ribavirin is replaced by a potent protease inhibitor, relapse is significantly increased and SVR is reduced. The future of HCV treatment is to combine peginterferon and ribavirin with several protease and/or polymerase inhibitors. Whether this strategy will allow ribavirin to be removed from the treatment paradigm remains to be proven. However, based on the results of clinical trials conducted to date, it is much more likely that peginterferon, not ribavirin, could be expendable.

Ribavirin and IFN-α combination therapy induces CD4+ T-cell proliferation and Th1 cytokine secretion in patients with chronic hepatitis B

AIM: To investigate the anti-viral mechanism of combination therapy of interferon (IFN)-α and ribavirin in patients with chronic hepatitis B.

METHODS: Twenty patients were assigned to receive either IFN-α plus ribavirin (group A, n = 14) or no treatment as a control (group B, n = 6). Patients were analyzed for T-cell proliferative responses specific for hepatitis B virus (HBV)-antigen and cytokine production by peripheral blood mononuclear cells (PBMCs).

RESULTS: Combination therapy induced HBV-antigen specific CD4+ T-cell proliferative responses in four patients (28.6%). Production of high levels of HBV-specific IFN-γ, tumor necrosis factor (TNF)-α, interleukin (IL)-12 by PBMCs was found in five patients (35.7%), who showed significantly lower HBV DNA levels in serum at 12 mo after treatment ended (P = 0.038) and at 24 mo of follow-up (P = 0.004) than those without high levels of cytokine production.

CONCLUSION: HBV-antigen specific CD4+ T cells may directly control HBV replication and secretion of anti-viral T helper 1 (Th1) cytokines by PBMCs during combination therapy of chronic hepatitis B with ribavirin and IFN-α.

Interferon-based treatment of chronic hepatitis C

The treatment of patients with chronic hepatitis C has rapidly evolved in the past 10 years centered on the use of interferon alpha 2 as an antiviral and immunomodulatory agent against hepatitis C virus. Firstly used as a monotherapy associated with a deceiving long-term efficacy, interferon alpha was then combined with ribavirin, a nucleoside analog with large antiviral properties. Combination of both drugs dramatically improved the efficacy of treatment with 50% of patients reaching a sustained viral response, characterized by the final eradication of the virus from the infected individual. Surprisingly, this synergistic effect remains greatly unexplained. The third step consisted in the use of pegylated interferon in order to adapt its pharmacokinetics and to allow a better efficacy with a more tolerable dosing schedule: once weekly subcutaneous injection instead of thrice weekly. Pegylated interferon combined with ribavirin during 24-48 weeks of treatment is the current standard of care with nearly 60% of sustained virologic response, overall. Development of new forms of interferon alpha are on the way with promising preliminary results.

Population pharmacokinetics of higher-dose mizoribine in healthy male volunteers

The population pharmacokinetic parameters of mizoribine in healthy subjects were estimated using a nonlinear mixed effects model (NONMEM) program. Pharmacokinetic data for population analysis were obtained in the previous study, in which 24 healthy Caucasian male subjects participated in a single-dose (3, 6, 9, 12 mg/kg) study, and 12 subjects participated in a multiple-dose (6, 12 mg/kg/d) study. The mean value of the absorption lag time, absorption rate constant (KA), and apparent distribution volume (V/F) was estimated to be 0.349 h, 0.869 h-1, and 0.834 l/kg, respectively. Oral clearance (CL/F) was modeled with creatinine clearance (CLcr), and the mean value was estimated to be 1.93.CLcr l/h. In addition, pharmacokinetic parameters in individual 36 subjects were obtained from population estimates according to Bayes' theorem. Pharmacokinetic parameters (KA, V/F, and CL/F) in the single-dose study were almost constant at a dose range of 3-12 mg/kg, and were similar to those in the multiple-dose study. These findings indicated that the pharmacokinetics of mizoribine is well described by a simple one-compartment model with first-order absorption.

Role of erythrocytes as a reservoir for ribavirin and relationship with adverse reactions in the early phase of interferon combination therapy for chronic hepatitis C virus infections

We investigated the relationship between serum ribavirin concentrations and clearance, as well as therapeutic efficacy and adverse reactions, in 97 Japanese patients with chronic hepatitis C virus infections treated with a 6-month course of high-dose alpha2b interferon (6 million units/day) plus ribavirin (600 to 800 mg/day) combination therapy. This randomized trial showed that the saturation of ribavirin uptake after taking ribavirin capsules does not occur within a dose range of 600 to 800 mg/day, which is a standard dosage used clinically in Japan. Serum ribavirin concentrations and clearance did not correlate with sustained virological response rates. Fourteen patients discontinued therapy because of adverse reactions, and sustained virological response rates were significantly reduced by discontinuation of therapy, while dose reduction of ribavirin did not alter the therapeutic effects. Ribavirin concentrations after 1 week and ribavirin clearance were significantly correlated with discontinuation of ribavirin; however, a multiple-regression analysis revealed that only hemoglobin concentration, but not ribavirin clearance, was a significant factor for discontinuation of therapy (odds ratio, 0.514; 95% confidence interval, 0.311 to 0.85; P = 0.0095). It appears that peripheral erythrocytes may act as a reservoir for ribavirin and regulate serum ribavirin levels in the very early phase of treatment.

Antisense approaches for inhibiting respiratory syncytial virus

Respiratory syncytial virus (RSV) continues as an emerging infectious disease not only among infants and children, but also for the immune-suppressed, hospitalised and the elderly. To date, ribavirin (Virazole, ICN Pharmaceuticals, Inc.) remains the only therapeutic agent approved for the treatment of RSV. However, its clinical benefits are small and occur only in a fraction of RSV-infected patients. The prophylactic administration of palivizumab (Synagis, MedImmune, Inc.) is problematic and costly and, therefore, only recommended for use in high-risk infants. Clearly, the need for an effective and safe drug remains high. This review discusses several different antisense approaches and compares them with traditional strategies, such as RSV-targeting antibodies and antivirals, as well as developments in vaccine research.

Ribavirin up-regulates IL-12 p40 gene expression and restores IL-12 levels in Leishmania-treated PBMCs

Ribavirin, a nucleoside analogue that interferes with viral mRNA synthesis and inhibits the replication of RNA and DNA viruses, has been recently proposed as an effective immune response modulator. In the present report, we studied the effect of ribavirin on IL-12 p40 gene expression in peripheral blood mononuclear cells (PBMCs) of healthy subjects. We also studied ribavirin effects on PBMCs activated with lipopolysaccharide (LPS) and phytohaemagglutinin (PHA) and treated with Leishmania donovani antigens. We provide evidence that ribavirin was able to up-regulate IL-12 p40 gene expression and to restore levels of IL-12 p40 gene expression and IL-12 secretion in fully activated PBMCs that were strongly inhibited by L. donovani antigens. Because effective management of leishmanial disease is usually associated with a prevalent T-helper 1 immune response with elevated production of IL-12,our preliminary results may be of particular interest, provided that they will be confirmed by further in vitro and in vivo studies, when considering a possible use of ribavirin as adjuvant in severe leishmanial disease.

Mechanism of action of T-705 against influenza virus

T-705, a substituted pyrazine compound, has been found to exhibit potent anti-influenza virus activity in vitro and in vivo. In a time-of-addition study, it was indicated that T-705 targeted an early to middle stage of the viral replication cycle but had no effect on the adsorption or release stage. The anti-influenza virus activity of T-705 was attenuated by addition of purines and purine nucleosides, including adenosine, guanosine, inosine, and hypoxanthine, whereas pyrimidines did not affect its activity. T-705-4-ribofuranosyl-5'-triphosphate (T-705RTP) and T-705-4-ribofuranosyl-5'-monophosphate (T-705RMP) were detected in MDCK cells treated with T-705. T-705RTP inhibited influenza virus RNA polymerase activity in a dose-dependent and a GTP-competitive manner. Unlike ribavirin, T-705 did not have an influence on cellular DNA or RNA synthesis. Inhibition of cellular IMP dehydrogenase by T-705RMP was about 150-fold weaker than that by ribavirin monophosphate, indicating the specificity of the anti-influenza virus activity and lower level of cytotoxicity of T-705. These results suggest that T-705RTP, which is generated in infected cells, may function as a specific inhibitor of influenza virus RNA polymerase and contributes to the selective anti-influenza virus activity of T-705.

Immunopharmacology of CpG oligodeoxynucleotides and ribavirin

To investigate their potential mechanisms of action, the nucleoside analogue ribavirin and a TLR9 agonist were compared. The CpG oligodeoxynucleotides (ODN) demonstrated strong TLR9-related Th1-type effects, and ribavirin appeared only to mediate signaling in TLR-transfected cells. CpG ODN represent a promising new type of therapeutic drug for hepatitis C or other infectious diseases.

Comparison of the inhibition of human metapneumovirus and respiratory syncytial virus by ribavirin and immune serum globulin in vitro

Human metapneumovirus (hMPV) is a newly recognized pathogen that like its better-known relative, human respiratory syncytial virus (hRSV), appears to be ubiquitous and an important cause of respiratory disease in diverse subpopulations. No antivirals or vaccines are currently approved for the treatment or prevention of hMPV infections. However, ribavirin is licensed to treat serious hRSV-induced infections in children and immune globulin designed for intravenous administration (i.v.IG) and palivizumab (Synagis), a humanized monoclonal antibody preparation, have been utilized as alternatives to vaccines for preventing or reducing the severity of infections caused by this virus. Because both ribavirin and i.v.IG have broad viral specificities, studies were performed to compare the ability of these two agents to inhibit the replication of hRSV and hMPV in tissue culture-based assays. Two experimental chemotherapeutic agents (i.e. VP14637 and JNJ2408068) and different antibody preparations were included in this testing for comparison. Ribavirin and the i.v.IG utilized were found to have equivalent antiviral activity against hMPV and hRSV. In contrast, except for antisera specifically raised against hMPV, all of the other materials tested had marked activity only against hRSV.

Pleiotropic mechanisms of ribavirin antiviral activities

Renewed interest in the mechanism of action of ribavirin results from its synergistic enhancement of interferon therapy and the need to develop more efficacious agents to treat hepatitis C virus infection. Since the discovery of ribavirin over 30 years ago by scientists at ICN Pharmaceuticals, many mechanisms of action for ribavirin have been proposed. These include inhibition of host inosine monophosphate dehydrogenase by ribavirin monophosphate, inhibition of viral capping enzymes, inhibition of viral RNA synthesis by ribavirin triphosphate, lethal mutagenesis of viral RNA genomes resulting from promiscuous incorporation of ribavirin triphosphate by the viral RNA polymerase, and modulation of the host immune responses. In this article, we will briefly review the evidence for these mechanisms, emphasizing recent findings. In addition, we will discuss strategies for development of nucleoside analogs that may replace ribavirin in the future.

The quest for an efficacious antiviral for respiratory syncytial virus

Respiratory syncytial virus (RSV) continues as an emerging infectious disease not only among infants and children, but also for the immune-suppressed, hospitalized and the elderly. To date, ribavirin (Virazole) remains the only therapeutic agent approved for the treatment of RSV. The prophylactic administration of palivizumab is problematic and costly. The quest for an efficacious RSV antiviral has produced a greater understanding of the viral fusion process, a new hypothesis for the mechanism of action of ribavirin, and a promising antisense strategy combining the 2'-5' oligoadenylate antisense (2-5A-antisense) approach and RSV genomics.

Current and future therapies of hepatitis C

With recent advances in the treatment of chronic hepatitis C, patients with elevated aminotransferase levels, detectable HCV RNA in the serum, and chronic inflammation are candidates for therapy. The best initial therapy is interferon plus ribavirin, achieving a sustained response rate in 40% of patients. The duration of therapy should be based on HCV genotype (48 weeks for genotype 1; 24 weeks for other genotypes). Serum HCV RNA should be measured at week 24 to assess response and guide further therapy in patients with genotype 1 infection. Patients unsuitable for combination therapy can be treated with interferon monotherapy. Side effects, dose modification and discontinuation are generally more frequent with interferon plus ribavirin, but can be managed with close follow-up and careful monitoring. With rapid developments in treatment, new therapies will require careful prospective evaluation according to HCV genotype and viral-load characteristics. Recommendations for therapy will probably change every few years, and novel approaches may provide effective therapy for most patients with hepatitis C.

Successful ribavirin therapy for life-threatening laryngeal papillomatosis post liver transplantation

A 3-yr-old girl developed severe progressive juvenile laryngeal papillomatosis (JLP) 2 yr after liver transplantation (Tx) for biliary atresia. The papillomata were resistant to withdrawal of immunosuppression, to laser surgery, and to subcutaneous interferon (3 MU/m2, three times weekly), necessitating tracheostomy. Oral ribavirin therapy (25 mg/kg/day) in combination with no immunosuppression effectively prevented the rapid recurrence of JLP over 5 yr. Hence, oral ribavirin is a potentially useful therapy in this life-threatening situation and may also be of benefit in other children with severe JLP.

The single dose pharmacokinetics of ribavirin in subjects with chronic liver disease

AIMS

The primary objective of this study was to describe the single dose pharmacokinetics of ribavirin in subjects with normal liver function and those with various degrees of stable chronic liver disease. Additionally this study assessed the safety and tolerability of ribavirin in this population.

METHODS

Single oral 600 mg doses of ribavirin were administered to healthy male and female volunteers (n = 6) and patients with stable chronic liver disease (n = 17), in a parallel group study. Pharmacokinetic sampling and tolerability assessments were performed up to 168 h post dose.

RESULTS

Single oral doses of 600 mg ribavirin were well tolerated by healthy volunteers and patients with varying degrees of hepatic dysfunction. Although mean Cmax increased with the severity of hepatic dysfunction, there was no change in extent of absorption or renal clearance of ribavirin.

CONCLUSIONS

There are no pharmacokinetic reasons for initial dose adjustment of ribavirin in patients with hepatic dysfunction.

Hepatitis C: an update on the silent epidemic

Hepatitis C virus (HCV) currently infects an estimated 2-3 million people in the United States and 175 million people globally. Over 80% of infected patients go on to develop chronic disease. Most patients remain asymptomatic despite silent, insidious progression of the disease. The sequelae of HCV-induced chronic liver disease accounts for 8,000-10,000 deaths annually in the United States and is currently the leading indication for liver transplantation. The cost of this epidemic to the United States was estimated in 1991 at $600 million in terms of medical expenses (excluding costs related to liver transplantation) and work lost. Over the last decade, since the viral genome of HCV was first sequenced in 1989, there has been a great increase in understanding of this infection. This review summarizes current knowledge about the hepatitis C epidemic with particular reference to epidemiology of infection, viral characteristics, risk factors for disease, diagnostic testing, clinical manifestations, and current, as well as potential, therapeutic options.

Mouse model of respiratory syncytial virus infection to evaluate antiviral activity in vivo

In this study, we have developed a practical mouse model for evaluating in vivo the antiviral activity of compounds against respiratory syncytial virus (RSV) infection. BALB/c mice are not particularly susceptible to RSV infection; however, infection rates were improved by pretreatment with the immunosuppressive agent cyclophosphamide (CYP). When mice were inoculated intranasally with RSV A2 strain, the pulmonary RSV titres of CYP-pretreated 10-week-old mice were higher than those of untreated 10-week-old and 28-week-old mice, peaking on days 4 and 5 post-infection. Sections of lung from RSV-infected mice pretreated with CYP, taken on day 4 post-inoculation, showed widespread evidence of interstitial pneumonia and other significant pathological changes. We also confirmed that ribavirin, a representative antiviral agent, significantly reduced the pulmonary RSV titres of mice pretreated with CYP when administered intraperitoneally.

Efficacy of RD3-0028 aerosol treatment against respiratory syncytial virus infection in immunosuppressed mice

RD3-0028, a benzodithiin compound, has antiviral activity against respiratory syncytial virus (RSV) in cell culture. We used a mouse model of RSV infection to determine the in vivo effect of RD3-0028. Cyclophosphamide (CYP)-treated, immunosuppressed mice were inoculated intranasally. The lungs of the mice were removed on day 4. The virus titers of the lungs of RD3-0028-treated mice were compared to the virus titers of the lungs of virus-inoculated, untreated control mice. In an effort to increase the therapeutic effectiveness of this compound, RD3-0028 was administered by aerosol to RSV-infected mice by using a head-exposure system. Aerosols generated from reservoirs containing RD3-0028 (7 mg/ml) administered for 2 h twice daily for 3 days significantly reduced the pulmonary titer of RSV-infected mice. It is clear that the minimal effective dose of RD3-0028 for RSV-infected mice is significantly less than that of ribavirin, the only compound currently available for use against RSV disease. Furthermore, the RD3-0028 aerosol administration appeared to protect the lungs of infected, CYP-treated mice against tissue damage, as evidenced by the preservation of the lung architecture and a reduction in pulmonary inflammatory infiltrates. RD3-0028 aerosol was not toxic for mice at the therapeutic dose. The present study demonstrates the effectiveness of aerosol administration of RD3-0028 for RSV-infected mice.

Effect of ribavirin on zidovudine efficacy and toxicity in vitro: a concentration-dependent interaction

Zidovudine (ZDV) is converted to its active triphosphate (ZDVTP) by intracellular kinases. The intermediate ZDV monophosphate (ZDVMP) is believed to play a major role in ZDV toxicity. Manipulation of ZDV phosphorylation is a possible therapeutic strategy for altering the risk-benefit ratio. Here we investigate whether combining RBV with ZDV is able to modulate efficacy and toxicity of ZDV. We have measured the intracellular activation of ZDV (0.3 microM) in the absence and presence of ribavirin (RBV; 2 and 20 microM) in Molt 4 and U937 cells. MTT cytotoxicity of ZDV (10-1000 microM) was also measured with and without RBV (2 microM) in Molt 4 and U937 cells. Measurement of endogenous deoxythymidine triphosphate (dTTP) allowed investigation of the dTTP/ZDVTP ratio. The antiviral efficacy of ZDV in combination with RBV (2 microM) was assessed by HIV p24 antigen measurements. In the presence of RBV (2 and 20 microM) a decrease in total ZDV phosphates was observed, owing mainly to an effect primarily on ZDVMP rather than the active ZDVTP. RBV also increased endogenous dTTP pools in both cell types, resulting in an increase in the dTTP/ZDVTP ratio. ZDV alone significantly reduced p24 antigen production, with an IC50 of 0.34 microM. Addition of RBV increased the IC50 approximately fivefold (1.52 microM). However, at higher concentrations of ZDV (10 and 100 microM) the antagonistic effect of RBV (2 microM) on ZDV was lost. The RBV-mediated decrease in ZDVMP may explain the reduction in ZDV toxicity when combined with RBV (2 microM). Cytotoxicity of ZDV was reduced in the presence of RBV (2 microM) at all concentrations in both cell lines, probably owing to saturation of ZDVTP formation. The interaction of ZDV and RBV is concentration dependent.