Novel coronavirus treatment with ribavirin: Groundwork for an evaluation concerning COVID‐19

Abstract Confronting the challenge of the outbreak of COVID‐19 should sharpen our focus on global drug access as a key issue in antiviral therapy testing. The testing and adoption of effective therapies for novel coronaviruses are hampered by the challenge of conducting controlled studies during a state of emergency. The access to direct antiviral drugs, such as ribavirin, that have an existing inventory and reliable supply chain may be a priority consideration for therapies developed for the 2019‐nCoV infection outbreaks and any strain variants that may emerge. On the basis of the direct antiviral activity of ribavirin against 2019‐nCoV in vitro and evidence for potency enhancement strategies developed during the prior SARS and MERS outbreaks, ribavirin may significantly impact our ability to end the lingering outbreaks in China and slow outbreaks in other countries. The apparent COVID‐19 pandemic provides an opportunity to follow dosage guidelines for treatment with ribavirin, test new therapeutic concepts, and conduct controlled testing to apply the scientific rigor required to address the controversy around this mainstay of antiviral therapy.


| ROLE FOR RIBAVIRIN IN 2019-nCoV TREATMENT
The pathology of COVID-19 resembles that of the 2013 MERS-CoV and 2003 SARS-CoV infections such that the extrapolation of treatment guidance from those prior clinical experiences can provide guidance for the current outbreak of 2019-nCoV. 2 The current "rapid advice guidelines for the diagnosis of and treatment of 2019-nCoV" summarize the strong and weak recommendations for treatment on the basis of the current frontline clinical evidence from 170 confirmed cases. 3 In this expert perspective of available data, the use of the all-combination antiviral drug is still controversial. 3 As strain isolates of the 2019-nCoV are distributed for laboratory testing in cell-based and animal model systems, recommendations for treatment may be ascribed. The first 2019-nCoV viral strain submitted for laboratory testing was 2019BetaCoV/Wuhan/WIV04/20192 (WIV04), which was isolated from the lung fluid of one patient in a cohort of seven, six of whom worked in the proximity of the Wuhan seafood market. 4 Indeed, the earliest report of in vitro efficacy of five FDA-approved drugs with activity against WIV04 has been reported (ribavirin, penciclovir, nitazoxanide, nafamostat, and chloroquine). In addition, two experimental drugs (remdesivir and favipiravir) have also shown activity against WIV04. 5 The report of in vitro direct-acting antiviral activity against the 2019-nCoV establishes the earliest basis for clinical guidance. Treatment with chloroquine and ribavirin may permit some advantage in an outbreak due to immediate drug availability.
Indeed, as a single agent and due to its cost and availability in China, a chloroquine phosphate multicenter trial was possible, and this drug showed signals of apparent efficacy against 2019-nCoV. 6 In contrast, the signals of efficacy from lopinavir/ritonavir were reported from a single case report from the index patient treated in Korea, whose viral titers diminished after treatment. 7 Additional laboratory studies may enrich the understanding of synergistic combinations, and subsequent coordinated clinical experience will collectively inform treatment guidance during the 2019-nCoV outbreak. Moreover, from a large number of controlled clinical trials, comparative effectiveness will be better understood, including an investigation to evaluate the merit of the addition of ribavirin to lopinavir/ritonavir treatment in outbreak regions (

| RIBAVIRIN: BASIS OF ANTIVIRAL ACTIVITY
Ribavirin is a guanosine analog that interferes with the replication of RNA and DNA viruses. However, the antiviral activity of ribavirin is not limited to interference with polymerases, that is, the structure of ribavirin also interferes with RNA capping that relies on natural guanosine to prevent RNA degradation. Moreover, to further promote the destabilization of viral RNA, ribavirin inhibits natural guanosine generation by directly inhibiting inosine monophosphate dehydrogenase in a pathway that is vital for the production of the guanine precursor to guanosine. 17 Even when treatment incompletely blocks the virus from replicating, viral nucleic acid replication in the presence of ribavirin occurs with reduced fidelity, leading to the introduction of random mutations that can reduce the viability of the virus. 18 This mechanism of action may overcome structure-dependent modes of viral immune evasion in a patient and encourage the generation of protective immunity.
The indirect antiviral properties of ribavirin as mediated by the immune system were first observed in the treatment of patients with hepatitis whose symptoms improved without a reduction in the viral load. 19 Further study of the immune cells in these patients found that the antiviral Th1 arm of the immune system was boosted by ribavirin, and additional studies have indicated that the enhanced polarization of the immune response may be at the expense of regulatory T cells that suppress the immune response. [20][21][22] This mechanism of immune regulation is one rationale for the testing of ribavirin as an anticancer agent.
Ribavirin's multimodal antiviral properties may limit viral replication, reducing the patient's viral load, subsequent pathological tissue damage, and the risk of transmission. There is no knowledge regarding the dosage required to experience each of the unique mechanisms of action of ribavirin, and it is also not known whether the relative threshold for the activity will vary among different patient populations and clinical contexts. A direct viral replicative inhibition is not the exclusive determinant of ribavirin's multimodal antiviral activity. Ribavirin's multiple mechanisms of action likely support its longevity and quality as a clinical resource.
As a very mature drug, with significant pharmacological research behind it, the pharmacokinetics and bioavailability data for ribavirin are available to inform dosing both as a single agent and as a part of combination therapies. 23 The clinical experience with ribavirin in the pediatric setting for respiratory syncytial virus infection and in the chronic infection setting for hepatitis C offers a wealth of practitioner experience with its safety profile and efficacy. [24][25][26] To achieve efficacy in these two distinct clinical settings, ribavirin is delivered either as an aerosol form or orally. However, concerning the use of CoV, all reports indicate IV or oral dosing.
The mean bioavailability of a 400-mg dose of ribavirin is 51.8% ± 21.8% after an IV loading dose of 150 mg. Using a threecompartment model for PK analysis, the mean gamma phase halflife is 37.0 ± 14.2 hours. Ribavirin is rapidly absorbed and has a T-max after the oral administration of 1 hour after the first dose, 1.7 hours after the second dose, and 3 hours after the multipledose. The route of ribavirin elimination is renal. 23,27 The average peak serum level of ribavirin in human is 24 µg/mL after a 1000mg IV dose (Box 1). 28 The coronavirus encodes RNA replication proofreading machinery that can partially resist one mechanism of action of nucleoside analogs, placing additional importance on our ability to determine therapeutic doses of ribavirin. 42 However, this resistance does not preclude the testing of other nucleoside analogs, such as remdesivir, in cases of 2019-nCoV. 43 The knowledge of this mode of nCoV resistance to nucleoside analogs may merit the consideration of testing ribavirin with remdesivir to reduce the emergence of treatmentresistant strains on the basis of mutations in the genes that encode the RNA replication machinery. 44

| RIBAVIRIN EXPERIENCE IN THE MERS-CoV OUTBREAK
In the pursuit of better treatment of MERS-CoV, multiple assay cell lines were used to test for antiviral activity against the strain KHALILI ET AL.

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hCoV-EMC/2012, yielding insights into ribavirin. 28 The IC-50 dose of ribavirin required to achieve direct antiviral activity toward hCoV-EMC/2012 exceeded the level achievable in humans using the standard assay cell line Vero-RML6, for which direct antiviral activity of ribavirin is now available for 2019-nCoV. 4,45 In this study, the LLC-MK2 cell-based assay was identified as a model host for the evaluation of ribavirin's antiviral properties against hCoV-EMC/ 2012. 45 Comparatively, the standard Vero-RML6 cell-based assay is defective in facilitating the multimodal activity of ribavirin because it is limited in its capacity to convert ribavirin into its mono-and  16 Using this dosing schedule and in combination with weekly IFN, the ribavirin was well tolerated. Significant adverse events in the treatment group included anemia, which was determined as a twofold mean decrease in hemoglobin (4.32 vs 2.14 g/L). The discontinuation of therapy was not required.
This treatment combination for MERS-CoV was deployed for the limited number of cases in Korea. 46 However, a retrospective study from the primarily affected region of MERS-CoV reviewed cases treated with ribavirin paired with IFN-α2b, and it was unable to establish a definitive therapeutic benefit, a conclusion that was attributed to the nature of the retrospective and uncontrolled study design. 30 To date, the 44-patient, single-institution experience demonstrating the benefit of ribavirin is considered to be the best evidence of a ribavirin treatment combination for coronavirus infection. In a systematic review of treatment options for MERS, the IFN-β/ribavirin combination therapy was suggested on the basis of a positive risk-benefit profile, whereas ribavirin monotherapyassociated toxicity was noted and thus assumed to not likely provide sufficient benefit to outweigh the toxicity. 47 However, the most encouraging evidence for the progressive evolution of treatment is the demonstration of tolerability of lopinavir/ritonavir, ribavirin, and IFN-α2a in a case study of MERS-CoV, suggesting that this combination should be tested as a treatment for 2019-nCoV. 48

CONFLICTS OF INTEREST
The authors disclose that their affiliated organizations will support clinical trials with ribavirin for the treatment of novel coronavirus infections.