Ribavirin enters cerebrospinal fluid

Antiviral Therapy of Haemorrhagic Fevers and Arbovirus Infections

RNA viruses of the families Arena-, Bunya-, Filo-, Flavi-and Togaviridae cause illness in humans ranging from mild, non-specific febrile syndromes to fulminant, lethal haemorrhagic fever. They are transmitted from animals to humans and from human to human by arthropods, aerosols or contact with body fluids. Antiviral compounds, convalescent plasma and interferon inhibit many of these agents in vitro and in virus-infected animals. Drug or plasma treatment is now in use for several human diseases, and would probably be beneficial for a number of others for which there is only limited treatment experience. Success is linked to early diagnosis and initiation of therapy. Ribavirin is used to treat Lassa fever and haemorrhagic fever with renal syndrome, and would probably be effective for Crimean-Congo haemorrhagic fever and for all New World arenavirus diseases. The value of ribavirin in the early treatment of hantavirus pulmonary syndrome is under evaluation. Convalescent plasma is the therapy of choice for Argentine haemorrhagic fever, and would also probably be effective for other New World arenaviruses and some other infections if a safe supply of plasma could be maintained. Ribavirin and interferon-α have both shown protective efficacy in non-human primates infected with Rift Valley fever virus. No effective therapy has yet been identified for filovirus infections, but results in animal models are encouraging. More clinical research is urgently needed. Even if placebo-controlled drug trials cannot be performed, conscientious reports of the results of therapy in limited numbers of patients can still provide evidence of antiviral drug effects.

Survival from rabies encephalitis

Rabies is a major public health problem in Asia and Africa, with nearly 60,000 deaths every year, and represents a substantial economic burden. Neurologists frequently encounter atypical cases, and need to make informed decisions regarding diagnosis and management. No therapy has been shown to unequivocally improve survival in rabies till date. Despite the overwhelmingly fatal nature of this disease, a small number of patients have been reported to survive acute rabies encephalitis with varying degrees of neurological sequelae. This paper presents the eleventh documented case of survival from rabies, which developed after being bitten by a stray dog, albeit with severe neurological residua. Similar to patients in previous reports, this man demonstrated a robust immune response as indicated by peripheral viral clearance and very high serum and cerebrospinal fluid antibody titres. Immunologically-mediated virus clearance therefore appears to be a prerequisite for survival. A detailed review of previously reported survivors, as well as descriptions of the host response and viral clearance in human rabies, current therapy for this disease and future directions in improving the currently dismal prognosis are provided.

Extinction of hepatitis C virus by ribavirin in hepatoma cells involves lethal mutagenesis

Lethal mutagenesis, or virus extinction produced by enhanced mutation rates, is under investigation as an antiviral strategy that aims at counteracting the adaptive capacity of viral quasispecies, and avoiding selection of antiviral-escape mutants. To explore lethal mutagenesis of hepatitis C virus (HCV), it is important to establish whether ribavirin, the purine nucleoside analogue used in anti-HCV therapy, acts as a mutagenic agent during virus replication in cell culture. Here we report the effect of ribavirin during serial passages of HCV in human hepatoma Huh-7.5 cells, regarding viral progeny production and complexity of mutant spectra. Ribavirin produced an increase of mutant spectrum complexity and of the transition types associated with ribavirin mutagenesis, resulting in HCV extinction. Ribavirin-mediated depletion of intracellular GTP was not the major contributory factor to mutagenesis since mycophenolic acid evoked a similar decrease in GTP without an increase in mutant spectrum complexity. The intracellular concentration of the other nucleoside-triphosphates was elevated as a result of ribavirin treatment. Mycophenolic acid extinguished HCV without an intervening mutagenic activity. Ribavirin-mediated, but not mycophenolic acid-mediated, extinction of HCV occurred via a decrease of specific infectivity, a feature typical of lethal mutagenesis. We discuss some possibilities to explain disparate results on ribavirin mutagenesis of HCV.

A multi-step process of viral adaptation to a mutagenic nucleoside analogue by modulation of transition types leads to extinction-escape

Resistance of viruses to mutagenic agents is an important problem for the development of lethal mutagenesis as an antiviral strategy. Previous studies with RNA viruses have documented that resistance to the mutagenic nucleoside analogue ribavirin (1-β-D-ribofuranosyl-1-H-1,2,4-triazole-3-carboxamide) is mediated by amino acid substitutions in the viral polymerase that either increase the general template copying fidelity of the enzyme or decrease the incorporation of ribavirin into RNA. Here we describe experiments that show that replication of the important picornavirus pathogen foot-and-mouth disease virus (FMDV) in the presence of increasing concentrations of ribavirin results in the sequential incorporation of three amino acid substitutions (M296I, P44S and P169S) in the viral polymerase (3D). The main biological effect of these substitutions is to attenuate the consequences of the mutagenic activity of ribavirin —by avoiding the biased repertoire of transition mutations produced by this purine analogue—and to maintain the replicative fitness of the virus which is able to escape extinction by ribavirin. This is achieved through alteration of the pairing behavior of ribavirin-triphosphate (RTP), as evidenced by in vitro polymerization assays with purified mutant 3Ds. Comparison of the three-dimensional structure of wild type and mutant polymerases suggests that the amino acid substitutions alter the position of the template RNA in the entry channel of the enzyme, thereby affecting nucleotide recognition. The results provide evidence of a new mechanism of resistance to a mutagenic nucleoside analogue which allows the virus to maintain a balance among mutation types introduced into progeny genomes during replication under strong mutagenic pressure.

Viruses that have RNA as genetic material include many important human, animal and plant pathogens. A new strategy against RNA viruses consists in using mutagenic nucleotides. The objective is to provoke an excessive number of mutations, to deteriorate the viral functions to the point that the virus can not survive. One of the mutagens used in research on lethal mutagenesis is ribavirin, extensively employed in clinical practice. Unfortunately, viral mutants that are resistant to ribavirin have been selected, thus facilitating escape from lethal mutagenesis. Here we describe a new mechanism by which foot-and-mouth disease virus (FMDV) can become resistant to ribavirin. Amino acid changes in the viral polymerase, selected by ribavirin, are able to modify the types of mutations produced in the presence of ribavirin. Biochemical data indicate that the alteration of the enzyme changes the pairing behavior of ribavirin, avoiding the production of an excess of some types of mutations, supporting the hypothesis that an unbalanced mutation repertoire is detrimental to the virus. Thus, this new mechanism of resistance to ribavirin is based not as much in limiting the number of mutations in the virus genetic material but in ensuring an equilibrium among different types of mutations that favors viral survival.

The use of oral ribavirin in the management of La Crosse viral infections

Since its recognition in 1964, La Crosse (LAC) virus has been recognized as an important cause of pediatric encephalitis in the United States. The annual incidence of this illness is believed to be between 20 and 30 cases per hundred thousand, though most cases remain undiagnosed. It is typically responsible for a relatively mild disease in humans, though a sub-group of patients suffer from life-threatening illness characterized by permanent neuropsychiatric sequelae. There are currently no approved medications to treat LAC viral infections. However, an anti-RNA viral treatment might prove useful in reducing the length and severity of illness while potentially reducing the risk of permanent sequelae. Evidence exists that the use of ribavirin may form the basis of an effective treatment for LAC viral infections. We propose that oral ribavirin may provide a useful treatment to limit the severity and improve the prognosis of those suffering from LAC viral infections.

The time-course of ribavirin-provoked changes of basal and AMPH-induced motor activities in rats

The time-course of changes of basal and amphetamine (AMPH)-induced locomotor and stereotypic activities in adult male Wistar rats after a single ribavirin injection was studied. In the first set of experiments, 10, 20 or 30 mg ribavirin/kg body weight (b.w.) were injected i.p. to rats and their basal motor activities were recorded every 10 min for 2 h and compared with those of saline-treated controls. In the second set of experiments, the animals were pretreated with ribavirin and 20 min later i.p. injected with AMPH (1.5 mg/kg b.w.). The controls received AMPH 20 min after the saline injection. Motor activity was recorded after the first injection and until 120 min after AMPH administration. Ribavirin did not significantly affect the time-course of either basal locomotor or stereotypic activities. Pretreatment with any of the applied ribavirin doses decreased the AMPH-induced hyperlocomotor response. However, the most pronounced effect was observed with ribavirin doses of 20 mg/kg and 30 mg/kg when administered during the first 10 min and 30 min after the AMPH injection respectively. In contrast, the stereotypic activities of these animals were only slightly changed. These results indicate a different susceptibility of regions in the basal ganglia to ribavirin.

Curing of foot-and-mouth disease virus from persistently infected cells by ribavirin involves enhanced mutagenesis

BHK-21 cells persistently infected with foot-and-mouth disease virus (FMDV) can be cured of virus by treatment with the antiviral nucleoside analogue ribavirin. To study whether the process involved an increase in the number of mutations in the mutant spectrum of the viral population, viral genomes were cloned from persistently infected cells treated or untreated with ribavirin. An increase of up to 10-fold in mutation frequencies associated with ribavirin treatment was observed in the viral genomes from the treated cultures as compared with parallel, untreated cultures. To address the possible mechanisms of enhanced mutagenesis, we investigated the mutagenic effects of ribavirin together with guanosine, and mycophenolic acid in the presence or absence of guanosine. Changes in the intracellular nucleotide concentrations were determined for all treatments. The results suggest that the increased mutation frequencies were not dependent on nucleotide pool imbalances or due to selection of preexisting genomes but they were produced by a mutagenic action of ribavirin.

Management of rabies in humans

Rabies is a fatal disease in humans, and, to date, the only survivors of the disease have received rabies vaccine before the onset of illness. The approach to management of the rabies normally should be palliative. In unusual circumstances, a decision may be made to use an aggressive approach to therapy for patients who present at an early stage of clinical disease. No single therapeutic agent is likely to be effective, but a combination of specific therapies could be considered, including rabies vaccine, rabies immunoglobulin, monoclonal antibodies, ribavirin, interferon-alpha, and ketamine. Corticosteroids should not be used. As research advances, new agents may become available in the future for the treatment of human rabies.

Treatment of subacute sclerosing panencephalitis with interferon-alpha, ribavirin, and inosiplex

Subacute sclerosing panencephalitis is an almost universally fatal late complication of measles infection for which there is no established treatment. We report a patient with subacute sclerosing panencephalitis who was bed-bound and ataxic and had a left hemiparesis and frequent myoclonus. He was started on a new regimen consisting of intraventricular interferon-alpha (starting at 100,000 U/m2/day, building up to 1 million U/m2/day), ribavirin (60 mg/kg/day intravenously), and inosiplex (3 g/day) and improved markedly. At 10 weeks, the intraventricular reservoir was removed because of bacterial infection, and he was discharged home on oral ribavirin (1200 mg/kg/day) and inosiplex. He continued to improve as judged by neurologic examination, functional independence measurement, neuropsychometry and single photon emission computed tomography (SPECT) imaging. However, after 10 months, he deteriorated suddenly and died before further intraventricular treatment could be instituted. Further trials are needed to evaluate long-term combination therapy in subacute sclerosing panencephalitis.

Effective ribavirin concentration in hamster brains for antiviral chemotherapy for subacute sclerosing panencephalitis

The ribavirin concentration in hamster brains was measured by a high-performance liquid chromatography (HPLC) system and a bioassay system. When ribavirin was administered intracranially at a dosage of 10 mg/kg of body weight per day for 10 days, a dosage which results in 100% survival of hamsters infected with subacute sclerosing panencephalitis (SSPE) virus and which inhibits the replication of SSPE virus in hamster brains, the ribavirin concentration in the brains estimated by HPLC and bioassay was kept higher than 50 micrograms/g for 10 days. The effective concentration in vivo corresponds to the concentration at which ribavirin completely inhibits the replication of SSPE virus in vitro. The maximal tolerable ribavirin concentration for hamsters was calculated to be 150 micrograms/g. Although ribavirin shows toxicity to the animals at a relatively low concentration (250 to 400 micrograms/g), intrathecal or intraventricular administration of ribavirin should be explored for potential use in the treatment of patients with SSPE, while the ribavirin concentration in cerebrospinal fluid or brain tissue should be monitored.

Safety, tolerance, and pharmacokinetics of systemic ribavirin in children with human immunodeficiency virus infection

Eleven pediatric patients, aged 1 to 10 years and with symptomatic human immunodeficiency virus infection, were treated with 6 or 10 mg of oral ribavirin per kg of body weight daily for 60 days. Safety and pharmacokinetic parameters were monitored; five children had comprehensive pharmacokinetic evaluations. The children tolerated the drug well, and treatment was not associated with any clinically significant adverse effects. Peak concentrations in plasma of 2.5 and 3.0 microM were reached at 90 min after single oral doses of 6 and 10 mg/kg, respectively. The mean systemic availability of oral ribavirin was 42.3%. After 60 days of ribavirin administration, mean trough concentrations in plasma of 2.6 and 4.1 microM were obtained. Ribavirin penetrated well into the cerebrospinal fluid, achieving 70% of the concentration in plasma at steady state.

Chronic enteroviral meningoencephalitis in agammaglobulinemia: case report and literature review

Chronic enteroviral meningoencephalitis is a well-recognized complication in patients with X-linked agammaglobulinemia (XLA). The majority of published cases refers to its occurrence in patients on no replacement therapy or on only intramuscular immunoglobulin. The advent of intravenous immunoglobulin (IVIg) in the early 1980s and its widespread use in XLA was thought to have virtually eradicated enteroviral meningoencephalitis in these patients. We describe the development of echovirus meningoencephalitis in an 11-year-old boy on regular IVIg replacement whose serum IgG levels were maintained at between 6 and 8 g/L (NR 6-13 g/L). Treatment with daily high-dose IVIg was commenced, with significant clinical improvement being noted within a few weeks in association with a reduction in blood-brain barrier permeability. The persistence of live virus, however, necessitated the use of intraventricular immunoglobulin. The virus proved resistant to two courses of specific intraventricular immunoglobulin and a 6-week course of oral ribavirin and eventually proved fatal 5 months after presentation. In view of the therapeutic uncertainties we have reviewed the use of immunoglobulin in the treatment of enteroviral meningoencephalitis over the past 6 years.

Antiviral therapy: current concepts and practices

Drugs capable of inhibiting viruses in vitro were described in the 1950s, but real progress was not made until the 1970s, when agents capable of inhibiting virus-specific enzymes were first identified. The last decade has seen rapid progress in both our understanding of antiviral therapy and the number of antiviral agents on the market. Amantadine and ribavirin are available for treatment of viral respiratory infections. Vidarabine, acyclovir, ganciclovir, and foscarnet are used for systemic treatment of herpesvirus infections, while ophthalmic preparations of idoxuridine, trifluorothymidine, and vidarabine are available for herpes keratitis. For treatment of human immunodeficiency virus infections, zidovudine and didanosine are used. Immunomodulators, such as interferons and colony-stimulating factors, and immunoglobulins are being used increasingly for viral illnesses. While resistance to antiviral drugs has been seen, especially among AIDS patients, it has not become widespread and is being intensely studied. Increasingly, combinations of agents are being used: to achieve synergistic inhibition of viruses, to delay or prevent resistance, and to decrease dosages of toxic drugs. New approaches, such as liposomes carrying antiviral drugs and computer-aided drug design, are exciting and promising prospects for the future.

Aerosol and intraperitoneal administration of ribavirin and ribavirin triacetate: pharmacokinetics and protection of mice against intracerebral infection with influenza A/WSN virus

Ribavirin is active in vitro but not in vivo against a number of viruses capable of causing encephalitis. Ribavirin triacetate (RTA), a lipophilic derivative, has been reported to be more effective than ribavirin in protecting animals from encephalitis. By using an influenza A/WSN virus encephalitis model, we demonstrated that RTA administered by small-particle aerosol was able to decrease the death rate and increase the time of survival. To determine if this beneficial effect was due to increased delivery of drug, the pharmacokinetic properties of ribavirin and RTA when administered as an aerosol or by intraperitoneal injection were examined. Aerosol administration of ribavirin or RTA gave significantly higher concentrations of ribavirin in the lungs and serum of mice than did intraperitoneal injection. There was no difference, however, in ribavirin levels when either ribavirin or RTA was administered by small-particle aerosol. In brain tissue, ribavirin concentrations increased with time and did not appear to decrease as rapidly as in lungs and serum. Mean peak ribavirin concentrations in the brain were higher following aerosol administration of ribavirin than RTA, and both were higher than that following intraperitoneal injection of either drug. Administration of ribavirin or RTA by intraperitoneal injection failed to protect mice from a lethal intracerebral inoculation of influenza A/WSN virus, while aerosolized RTA did protect mice. The pharmacokinetics of ribavirin in brain tissue following aerosol administration of either drug did not explain the advantage of RTA over ribavirin in protecting mice from intracerebral infection with influenza A/WSN virus.

Therapy of viral infections of the central nervous system

The herpesviruses (particularly HSV) are the only CNS viral infections for which reasonably clear guidelines exist for specific antiviral treatment. However, data are also beginning to emerge for specific antiviral therapy of HIV-associated CNS disease despite the lack of a clear understanding of the pathogenesis of the CNS abnormalities. As the pace of antiviral drug development increases it is likely that a wider range of CNS viral infections will be treatable in the future although entry into the CNS is likely to remain a problem limiting the successful application of many compounds to CNS infection.

Mechanism of La Crosse virus inhibition by ribavirin

The effect of ribavirin on the growth and replication of La Crosse virus was examined. The data suggest that low concentrations of ribavirin have a marked effect on the initial steps of La Crosse virus transcription. The therapeutic potential of ribavirin in the treatment of human California encephalitis serotype infections is discussed in light of these findings.

Failure of interferon alfa and tribavirin in rabies encephalitis

OBJECTIVE

To test the effect of interferon alfa and tribavirin (ribavirin) in patients with rabies encephalitis.

DESIGN

An open trial of chemotherapy and intensive care in patients with early rabies.

SETTING

The intensive care unit of a Bangkok hospital.

PATIENTS

Four conscious men with clinical rabies encephalitis.

INTERVENTIONS

Rapid virological diagnosis of rabies. Treatment with intravenous and intraventricular injections of high doses of lymphoblastoid interferon alfa in three patients and tribavirin in one patient. Intensive care was given throughout.

MAIN OUTCOME MEASURES

Rabies infection confirmed by antigen detection and virus isolation. Rabies neutralising antibody and specific IgM sought in serum and cerebrospinal fluid. Interferon concentrations monitored before and during treatment in three patients.

RESULTS

Interferon alfa treatment produced high concentrations in serum and cerebrospinal fluid. All four patients died after 5 1/2 to 12 1/2 days of treatment with no evidence of virostatic or clinically beneficial effects from either treatment.

CONCLUSION

Interferon alfa treatment is not effective in rabies encephalitis. The use of tribavirin warrants further study, possibly combined with new therapeutic methods.

Pharmacokinetics of ribavirin aerosol in mice

The pharmacokinetics of ribavirin administered in single or multiple treatments to mice by small-particle aerosol were monitored in lung, serum, and brain tissues. ribavirin aerosol was administered with a standard drug concentration (20 mg/ml) in the reservoir for 12 h or a high dose (60 mg/ml) for 2 or 4 h. After single or 3-day treatments, ribavirin rapidly accumulated in the lungs at concentrations sufficient to inhibit influenza virus or respiratory syncytial virus (1 to 5 mM). While peak levels of ribavirin in the lungs after the high-dose administration were about three times those found with the standard dose, ribavirin was rapidly cleared from the lungs. There was no accumulation of drug in the lungs after multiple treatments. Ribavirin cleared from the lungs was detected in the blood within 15 min. Concentrations in the serum were similar (20 to 30 microM) for standard- and high-dose treatments with either single or multiple treatments. Ribavirin clearance from the serum after treatment was similar for each regimen. Ribavirin also rapidly accumulated in the brain to a similar level (ca. 6 nmol per brain) after standard- or high-dose treatment for 3 days. In contrast to ribavirin in the serum, ribavirin in the brain appeared to be slowly cleared, allowing levels to remain relatively constant during and after treatment. With the interest in viral encephalopathies, further evaluation of the possible advantages of this method of drug administration is warranted.

Antiviral therapy in AIDS. Clinical pharmacological properties and therapeutic experience to date

The rapid spread of human immunodeficiency virus (HIV) infections and the grim outcome of these infections have focused interest on the possibilities for medical intervention. The end-stage of these infections, acquired immune deficiency syndrome (AIDS), was first recognised in 1981, and the causative agent isolated in 1983. Already several antiviral drugs have been investigated. One initially promising drug, suramin, was found to have a net harmful effect but another, zidovudine (azidothymidine) has been shown to prolong life in AIDS patients. The properties of these and several other antiviral drugs such as antimoniotungstate (HPA-23), foscarnet (phosphonoformate) ribavirin, dideoxynucleotides, and interferons, are reviewed. The role of immunomodulating modalities such as plasmapheresis, bone marrow transplantation, thymosin, interleukin-2, inosine pranobex (isoprinosine), and cyclosporin are also discussed. None of the currently available drugs hold promise as monotherapy. Through analysis of the experience with these drugs and the increasing knowledge of HIV pathogenesis, new drugs can be designed. It seems increasingly clear that drugs will eventually have to be used in combination in order to reduce toxicity, exploit therapeutic synergy, and reduce the risk of HIV resistance. The theoretical and experimental background for such combinations are currently being elucidated.

Ribavirin antagonizes the effect of azidothymidine on HIV replication

Azidothymidine and ribavirin both inhibit replication of human immunodeficiency virus in vitro and show promise of clinical utility in patients infected with this virus. In this study, the possible interactions of these drugs were examined in vitro, and a reproducible antagonism between azidothymidine and ribavirin was found to occur under a variety of experimental conditions. The mechanism responsible for this antagonism appeared to be inhibition of azidothymidine phosphorylation by ribavirin. Because similar effects may occur in vivo, clinical trials of these two drugs in combination must be performed only under carefully controlled conditions.