Neuraminidase inhibitors: zanamivir and oseltamivir

Hazards of antiviral contamination in water: Dissemination, fate, risk and their impact on fish

Antiviral drugs are a cornerstone in the first line of antiviral therapy and their demand rises consistently with increments in viral infections and successive outbreaks. The drugs enter the waters due to improper disposal methods or via human excreta following their consumption; consequently, many of them are now classified as emerging pollutants. Hereby, we review the global dissemination of these medications throughout different water bodies and thoroughly investigate the associated risk they pose to the aquatic fauna, particularly our vertebrate relative fish, which has great economic and dietary importance and subsequently serves as a major doorway to the human exposome. Our risk assessment identifies eleven such drugs that presently pose high to moderate levels of risk to the fish. The antiviral drugs are likely to induce oxidative stress, alter the behaviour, affect different physiological processes and provoke various toxicological mechanisms. Many of the compounds exhibit elevated bioaccumulation potential, while, some have an increased tendency to leach through soil and contaminate the groundwater. Eight antiviral medications show a highly recalcitrant nature and would impact the aquatic life consistently in the long run and continue to influence the human exposome. Thereby, we call for urgent ecopharmacovigilance measures and modification of current water treatment methods.

Anti-rheumatic colchicine phytochemical exhibits potent antiviral activities against avian and seasonal Influenza A viruses (IAVs) via targeting different stages of IAV replication cycle

BACKGROUND

The continuous evolution of drug-resistant influenza viruses highlights the necessity for repurposing naturally-derived and safe phytochemicals with anti-influenza activity as novel broad-spectrum anti-influenza medications.

METHODS

In this study, nitrogenous alkaloids were tested for their viral inhibitory activity against influenza A/H1N1 and A/H5N1 viruses. The cytotoxicity of tested alkaloids on MDCK showed a high safety range (CC50 > 200 µg/ml), permitting the screening for their anti-influenza potential.

RESULTS

Herein, atropine sulphate, pilocarpine hydrochloride and colchicine displayed anti-H5N1 activities with IC50 values of 2.300, 0.210 and 0.111 µg/ml, respectively. Validation of the IC50 values was further depicted by testing the three highly effective alkaloids, based on their potent IC50 values against seasonal influenza A/H1N1 virus, showing comparable IC50 values of 0.204, 0.637 and 0.326 µg/ml, respectively. Further investigation suggests that colchicine could suppress viral infection by primarily interfering with IAV replication and inhibiting viral adsorption, while atropine sulphate and pilocarpine hydrochloride could directly affect the virus in a cell-free virucidal effect. Interestingly, the in silico molecular docking studies suggest the abilities of atropine, pilocarpine, and colchicine to bind correctly inside the active sites of the neuraminidases of both influenza A/H1N1 and A/H5N1 viruses. The three alkaloids exhibited good binding energies as well as excellent binding modes that were similar to the co-crystallized ligands. On the other hand, consistent with in vitro results, only colchicine could bind correctly against the M2-proton channel of influenza A viruses (IAVs). This might explicate the in vitro antiviral activity of colchicine at the replication stage of the virus replication cycle.

CONCLUSION

This study highlighted the anti-influenza efficacy of biologically active alkaloids including colchicine. Therefore, these alkaloids should be further characterized in vivo (preclinical and clinical studies) to be developed as anti-IAV agents.

Influenza virus cell entry and targeted antiviral development

Influenza virus infection is currently one of the most prevalent and transmissible diseases in the world causing local outbreaks every year. It has the potential to cause devastating global pandemics as well. The development of anti-influenza drugs possessing novel mechanisms of action is urgently needed to control the spread of influenza infections; thus, drugs that inhibit influenza virus entry into target cells are emerging as a hot research topic. In addition to discussing the biological significance of hemagglutinin in viral replication, this article provides recent updates on the natural products, small molecules, proteins, peptides, and neutralizing antibody-like proteins that have anti-influenza potency.

Influenza Treatment: Limitations of Antiviral Therapy and Advantages of Drug Combination Therapy

Influenza infection is serious and debilitating for humans and animals. The influenza virus undergoes incessant mutation, segment recombination, and genome reassortment. As a result, new epidemics and pandemics are expected to emerge, making the elimination challenging of the disease. Antiviral therapy has been used for the treatment of influenza since the development of amantadine in the 1960s; however, its use is hampered by the emergence of novel strains and the development of drug resistance. Thus, combinational therapy with two or more antivirals or immunomodulators with different modes of action is the optimal strategy for the effective treatment of influenza infection. In this review, we describe current options for combination therapy, their performance, and constraints imposed by resistance, calling attention to the advantages of combination therapy against severe influenza infections. We also discuss the challenges of influenza therapy and the limitations of approved antiviral drugs.

Influenza A virus strain PR/8/34, but neither HAM/2009 nor WSN/33, is transiently inhibited by the PB2-targeting drug paliperidone

Influenza A virus (FLUAV) is a significant human pathogen. In silico structural analysis (PMID 28628827) has suggested that the FDA-approved drug paliperidone interferes with the binding of the FLUAV polymerase subunit PB2 to the nucleoprotein NP. We found that paliperidone inhibits FLUAV A/PR/8/34 early after infection of canine MDCK II, human A549, and human primary bronchial cells, but not at late time points. No effect was detectable against the strains A/Hamburg/05/2009 and A/WSN/33. Moreover, paliperidone indeed disturbed the interaction between the PB2 and the NP of A/PR/8/34 and reduced early viral RNA and protein synthesis by approximately 50%. Thus, paliperidone has measurable but transient and virus-strain-restricted effects on FLUAV.

Emerging antiviral therapies and drugs for the treatment of influenza

INTRODUCTION

Both vaccines and antiviral drugs represent the mainstay for preventing and treating influenza. However, approved M2 ion channel inhibitors, neuraminidase inhibitors, polymerase inhibitors, and various vaccines cannot meet therapeutic needs because of viral resistance. Thus, the discovery of new targets for the virus or host and the development of more effective inhibitors are essential to protect humans from the influenza virus.

AREAS COVERED

This review summarizes the latest progress in vaccines and antiviral drug research to prevent and treat influenza, providing the foothold for developing novel antiviral inhibitors.

EXPERT OPINION

Vaccines embody the most effective approach to preventing influenza virus infection, and recombinant protein vaccines show promising prospects in developing next-generation vaccines. Compounds targeting the viral components of RNA polymerase, hemagglutinin and nucleoprotein, and the modification of trusted neuraminidase inhibitors are future research directions for anti-influenza virus drugs. In addition, some host factors affect the replication of virus in vivo, which can be used to develop antiviral drugs.

Platelet Desialylation Is a Novel Mechanism and Therapeutic Target in Daboia siamensis and Agkistrodon halys Envenomation-Induced Thrombocytopenia

Venom-induced thrombocytopenia (VIT) is one of the most important hemotoxic effects of a snakebite, which is often associated with venom-induced consumptive coagulopathy (VICC). Refractory thrombocytopenia without significant coagulation abnormalities has also been reported after envenomation by some viperid snakes; however, the mechanisms are not well understood and therapeutic strategies are lacking. Here, we found that patients injured by Daboia siamensis or Agkistrodon halys snakes, who were resistant to standard antivenom treatment, had developed coagulopathy-independent thrombocytopenia. Venoms from these viperid snakes, rather than from the elapid snake (Bungarus multicinctus), induced platelet surface expression of neuraminidase-1 (NEU-1), and significantly increased the desialylation of the glycoproteins on human platelets. The desialylated platelets caused by viperid snake venoms were further internalized by macrophages, which resulted in reduced platelet numbers in peripheral blood. Importantly, neuraminidase inhibitor significantly decreased viper venom-induced platelet desialylation, therefore inhibiting platelet phagocytosis by macrophages, and alleviating venom-induced thrombocytopenia. Collectively, these findings support an important role for desialylated platelet clearance in the progression of viper envenomation-induced, coagulopathy-independent thrombocytopenia. Our study demonstrates that the neuraminidase inhibitor may be a potential therapy or adjuvant therapy to treat snakebite-induced thrombocytopenia.

Antiviral Drugs in Influenza

Flu is a serious health, medical, and economic problem, but no therapy is yet available that has satisfactory results and reduces the occurrence of these problems. Nearly 20 years after the registration of the previous therapy, baloxavir marboxil, a drug with a new mechanism of action, recently appeared on the market. This is a promising step in the fight against the influenza virus. This article presents the possibilities of using all available antiviral drugs specific for influenza A and B. We compare all currently recommended anti-influenza medications, considering their mechanisms of action, administration, indications, target groups, effectiveness, and safety profiles. We demonstrate that baloxavir marboxil presents a similar safety and efficacy profile to those of drugs already used in the treatment of influenza. Further research on combination therapy is highly recommended and may have promising results.

Dietary intervention with sialylated lactulose affects the immunomodulatory activities of mice

Four sialylated lactuloses [N-acetylneuraminic acid-α2,3-lactulose (Neu5Acα2,3lactulose), N-acetylneuraminic acid-α2,6-lactulose (Neu5Acα2,6lactulose), deaminoneuraminc acid-α2,3-lactulose (Kdnα2,3lactulose), and deaminoneuraminc acid-α-2,6-lactulose (Kdnα2,6lactulose)] were reported to modulate the immunity of mice. The influences of cytokine expression, cell immunity, humoral immunity, and nonspecific immunity were investigated in our study using several techniques. Analysis via ELISA showed that cytokine expression was induced by sialylated lactulose treatment consistently in the serum and spleen. Among the 4 tested sialylated lactuloses, Neu5Acα2,6lactulose performed the best, simultaneously and appropriately promoting the expression of proinflammatory and anti-inflammatory factors in the serum and spleen. Kdnα2,3lactulose showed the best antioxidant activity according to detection of the activity of superoxide dismutase, myeloperoxidase, peroxidase, and alkaline phosphatase. Flow cytometry revealed that only Kdnα2,3lactulose significantly boosted the CD3⁺ T lymphocyte ratio similarly to that of lactulose. Analysis of the hemolysin content to characterize humoral immunity revealed that Kdnα2,3lactulose notably increased hemolysin content compared with that in the control group. To evaluate the nonspecific immune effects of the 4 sialylated lactuloses, a fluorescence microsphere phagocytosis assay was used to analyze the phagocytosis of macrophages. Kdnα2,3lactulose still performed the best in enhancing the phagocytosis of macrophages, showing markedly increased phagocytic percentage and phagocytic index values compared with those in the control and lactulose groups. Comparing the differences of these 4 sialylated lactuloses in affecting immunity in mice revealed that Kdnα2,3lactulose had the best overall performance in influencing cytokine expression, cell immunity, humoral immunity, and nonspecific immunity. This study provides critical support for use of sialylated lactuloses as potential immunomodulators in foods.

The Anti-Viral and Anti-Inflammatory Properties of Edible Bird's Nest in Influenza and Coronavirus Infections: From Pre-Clinical to Potential Clinical Application

Edible bird's nest (BN) is a Chinese traditional medicine with innumerable health benefits, including anti-viral, anti-inflammatory, neuroprotective, and immunomodulatory effects. A small number of studies have reported the anti-viral effects of EBN against influenza infections using in vitro and in vivo models, highlighting the importance of sialic acid and thymol derivatives in their therapeutic effects. At present, studies have reported that EBN suppresses the replicated virus from exiting the host cells, reduces the viral replication, endosomal trafficking of the virus, intracellular viral autophagy process, secretion of pro-inflammatory cytokines, reorient the actin cytoskeleton of the infected cells, and increase the lysosomal degradation of viral materials. In other models of disease, EBN attenuates oxidative stress-induced cellular apoptosis, enhances proliferation and activation of B-cells and their antibody secretion. Given the sum of its therapeutic actions, EBN appears to be a candidate that is worth further exploring for its protective effects against diseases transmitted through air droplets. At present, anti-viral drugs are employed as the first-line defense against respiratory viral infections, unless vaccines are available for the specific pathogens. In patients with severe symptoms due to exacerbated cytokine secretion, anti-inflammatory agents are applied. Treatment efficacy varies across the patients, and in times of a pandemic like COVID-19, many of the drugs are still at the experimental stage. In this review, we present a comprehensive overview of anti-viral and anti-inflammatory effects of EBN, chemical constituents from various EBN preparation techniques, and drugs currently used to treat influenza and novel coronavirus infections. We also aim to review the pathogenesis of influenza A and coronavirus, and the potential of EBN in their clinical application. We also describe the current literature in human consumption of EBN, known allergenic or contaminant presence, and the focus of future direction on how these can be addressed to further improve EBN for potential clinical application.

Molecular Mechanism of Action of Repurposed Drugs and Traditional Chinese Medicine Used for the Treatment of Patients Infected With COVID-19: A Systematic Scoping Review

Background: The emergence of COVID-19 as a pandemic has resulted in the need for urgent development of vaccines and drugs and the conduction of clinical trials to fight the outbreak. Because of the time constraints associated with the development of vaccines and effective drugs, drug repurposing and other alternative treatment methods have been used to treat patients that have been infected by the SARS-CoV-2 virus and have acquired COVID-19. Objective: The objective of this systematic scoping review is to provide an overview of the molecular mechanism of action of repurposed drugs or alternative treatment medicines used to attenuate COVID-19 disease. Method: The research articles or gray literature, including theses, government reports, and official news online, were identified from four databases and one search engine. The full content of a total of 160 articles that fulfilled our inclusion criteria was analyzed and information about six drugs (ritonavir, lopinavir, oseltamivir, remdesivir, favipiravir, and chloroquine) and four Traditional Chinese Medicines (Shuang Huang Lian Kou Fu Ye, TCM combination of Bu Huan Jin Zheng Qi San and Da Yuan Yin, Xue Bi Jing Injection, and Qing Fei Pai Du Tang) was extracted. Results: All of the repurposed drugs and complementary medicine that have been used for the treatment of COVID-19 depend on the ability of the drug to inhibit the proliferation of the SARS-CoV-2 virus by binding to enzyme active sites, viral chain termination, or triggering of the molecular pathway, whereas Traditional Chinese Medicine plays a pivotal role in triggering the inflammation pathway, such as the neuraminidase blocker, to fight the SARS-CoV-2 virus.

The DHODH inhibitor PTC299 arrests SARS-CoV-2 replication and suppresses induction of inflammatory cytokines

The coronavirus disease 2019 (COVID-19) pandemic has created an urgent need for therapeutics that inhibit the SARS-COV-2 virus and suppress the fulminant inflammation characteristic of advanced illness. Here, we describe the anti-COVID-19 potential of PTC299, an orally bioavailable compound that is a potent inhibitor of dihydroorotate dehydrogenase (DHODH), the rate-limiting enzyme of the de novo pyrimidine nucleotide biosynthesis pathway. In tissue culture, PTC299 manifests robust, dose-dependent, and DHODH-dependent inhibition of SARS-COV-2 replication (EC50 range, 2.0-31.6 nM) with a selectivity index >3,800. PTC299 also blocked replication of other RNA viruses, including Ebola virus. Consistent with known DHODH requirements for immunomodulatory cytokine production, PTC299 inhibited the production of interleukin (IL)-6, IL-17A (also called IL-17), IL-17 F, and vascular endothelial growth factor (VEGF) in tissue culture models. The combination of anti-SARS-CoV-2 activity, cytokine inhibitory activity, and previously established favorable pharmacokinetic and human safety profiles render PTC299 a promising therapeutic for COVID-19.

Influenza Virus Neuraminidase Engages CD83 and Promotes Pulmonary Injury

Influenza A viruses cause severe respiratory illnesses in humans and animals. Overreaction of the innate immune response to influenza virus infection results in hypercytokinemia, which is responsible for mortality and morbidity. However, the mechanism by which influenza induces hypercytokinemia is not fully understood. In this study, we established a mouse-adapted H9N2 virus, MA01, to evaluate the innate immune response to influenza in the lung. MA01 infection caused high levels of cytokine release, enhanced pulmonary injury in mice, and upregulated CD83 protein in dendritic cells and macrophages in the lung. Influenza virus neuraminidase (NA) unmasked CD83 protein and contributed to high cytokine levels. Furthermore, we provide evidence that CD83 is a sialylated glycoprotein. Neuraminidase treatment enhanced lipopolysaccharide (LPS)-stimulated NF-κB activation in RAW264.7 cells. Anti-CD83 treatment alleviated influenza virus-induced lung injury in mice. Our study indicates that influenza virus neuraminidase modulates CD83 status and contributes to the "cytokine storm," which may suggest a new approach to curb this immune injury.IMPORTANCE The massive release of circulating mediators of inflammation is responsible for lung injury during influenza A virus infection. This phenomenon is referred to as the "cytokine storm." However, the mechanism by which influenza induces the cytokine storm is not fully understood. In this study, we have shown that neuraminidase unmasked CD83 protein in the lung and contributed to high cytokine levels. Anti-CD83 treatment could diminish immune damage to lung tissue. The NA-CD83 axis may represent a target for an interruption of influenza-induced lung damage.

Novel and potent inhibitors targeting DHODH are broad-spectrum antivirals against RNA viruses including newly-emerged coronavirus SARS-CoV-2

Emerging and re-emerging RNA viruses occasionally cause epidemics and pandemics worldwide, such as the on-going outbreak of the novel coronavirus SARS-CoV-2. Herein, we identified two potent inhibitors of human DHODH, S312 and S416, with favorable drug-likeness and pharmacokinetic profiles, which all showed broad-spectrum antiviral effects against various RNA viruses, including influenza A virus, Zika virus, Ebola virus, and particularly against SARS-CoV-2. Notably, S416 is reported to be the most potent inhibitor so far with an EC₅₀ of 17 nmol/L and an SI value of 10,505.88 in infected cells. Our results are the first to validate that DHODH is an attractive host target through high antiviral efficacy in vivo and low virus replication in DHODH knock-out cells. This work demonstrates that both S312/S416 and old drugs (Leflunomide/Teriflunomide) with dual actions of antiviral and immuno-regulation may have clinical potentials to cure SARS-CoV-2 or other RNA viruses circulating worldwide, no matter such viruses are mutated or not.

The DHODH Inhibitor PTC299 Arrests SARS-CoV-2 Replication and Suppresses Induction of Inflammatory Cytokines

The coronavirus disease 2019 (COVID-19) pandemic has created an urgent need for therapeutics that inhibit the SARS-CoV-2 virus and suppress the fulminant inflammation characteristic of advanced illness. Here, we describe the anti-COVID-19 potential of PTC299, an orally available compound that is a potent inhibitor of dihydroorotate dehydrogenase (DHODH), the rate-limiting enzyme of the de novo pyrimidine biosynthesis pathway. In tissue culture, PTC299 manifests robust, dose-dependent, and DHODH-dependent inhibition of SARS CoV-2 replication (EC ₅₀ range, 2.0 to 31.6 nM) with a selectivity index >3,800. PTC299 also blocked replication of other RNA viruses, including Ebola virus. Consistent with known DHODH requirements for immunomodulatory cytokine production, PTC299 inhibited the production of interleukin (IL)-6, IL-17A (also called IL-17), IL-17F, and vascular endothelial growth factor (VEGF) in tissue culture models. The combination of anti-SARS-CoV-2 activity, cytokine inhibitory activity, and previously established favorable pharmacokinetic and human safety profiles render PTC299 a promising therapeutic for COVID-19.

Novel and potent inhibitors targeting DHODH are broad-spectrum antivirals against RNA viruses including newly-emerged coronavirus SARS-CoV-2

Emerging and re-emerging RNA viruses occasionally cause epidemics and pandemics worldwide, such as the on-going outbreak of the novel coronavirus SARS-CoV-2. Herein, we identified two potent inhibitors of human DHODH, S312 and S416, with favorable drug-likeness and pharmacokinetic profiles, which all showed broad-spectrum antiviral effects against various RNA viruses, including influenza A virus, Zika virus, Ebola virus, and particularly against SARS-CoV-2. Notably, S416 is reported to be the most potent inhibitor so far with an EC₅₀ of 17 nmol/L and an SI value of 10,505.88 in infected cells. Our results are the first to validate that DHODH is an attractive host target through high antiviral efficacy in vivo and low virus replication in DHODH knock-out cells. This work demonstrates that both S312/S416 and old drugs (Leflunomide/Teriflunomide) with dual actions of antiviral and immuno-regulation may have clinical potentials to cure SARS-CoV-2 or other RNA viruses circulating worldwide, no matter such viruses are mutated or not.

Combined MS/MS-NMR Annotation Guided Discovery of Iris lactea var. chinensis Seed as a Source of Viral Neuraminidase Inhibitory Polyphenols

In this study, the chemical diversity of polyphenols in Iris lactea var. chinensis seeds was identified by combined MS/MS-NMR analysis. Based on the annotated chemical profile, the isolation of stilbene oligomers was conducted, and consequently, stilbene oligomers (1-10) were characterized. Of these, compounds 1 and 2 are previously undescribed stilbene dimer glycoside (1) and tetramer glycoside (2), respectively. Besides, to evaluate this plant seed as a rich source of stilbene oligomers, we quantified three stilbene oligomers of I. lactea var. chinensis seeds. The contents of three major stilbene oligomers—trans-ε-viniferin (3), vitisin A (6), and vitisin B (9)—in I. lactea var. chinensis seeds were quantified as 2.32 (3), 4.95 (6), and 1.64 (9) mg/g dry weight (DW). All the isolated compounds were tested for their inhibitory activities against influenza neuraminidase. Compound 10 was found to be active with the half maximal inhibitory concentration (IC₅₀) values at 4.76 μM. Taken together, it is concluded that I. lactea var. chinensis seed is a valuable source of stilbene oligomers with a human health benefit.

SARS-CoV-2: an Emerging Coronavirus that Causes a Global Threat

An ongoing outbreak of pneumonia caused by a novel coronavirus, currently designated as the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), was reported recently. However, as SARS-CoV-2 is an emerging virus, we know little about it. In this review, we summarize the key events occurred during the early stage of SARS-CoV-2 outbreak, the basic characteristics of the pathogen, the signs and symptoms of the infected patients as well as the possible transmission pathways of the virus. Furthermore, we also review the current knowledge on the origin and evolution of the SARS-CoV-2. We highlight bats as the potential natural reservoir and pangolins as the possible intermediate host of the virus, but their roles are waiting for further investigation. Finally, the advances in the development of chemotherapeutic options are also briefly summarized.

Sensitivity of Commercially Available Influenza Rapid Diagnostic Tests in the 2018-2019 Influenza Season

Epidemics of seasonal influenza caused by H1N1pdm09, H3N2, and type B viruses occur throughout the world. Sporadic human H5 and H7N9 virus infections are also reported in particular regions. To treat influenza patients effectively with antivirals, sensitive and broad-reactive influenza rapid diagnostic tests (IRDTs) are required. Here, we tested the sensitivity of 23 IRDTs during the 2018-2019 influenza season for their ability to detect H1N1pdm09, H3N2, H5N1, H5N6, H7N9, and Victoria- and Yamagata-lineage type B viruses. All IRDTs detected all influenza A and B viruses tested but with different sensitivities. Several IRDTs detected the H5 and H7 viruses and the seasonal viruses with similar sensitivity. Such IRDTs might be useful for diagnosing patients infected with H5 and H7 viruses.

The Future of Flu: A Review of the Human Challenge Model and Systems Biology for Advancement of Influenza Vaccinology

Objectives: Novel approaches to advance the field of vaccinology must be investigated, and are particularly of importance for influenza in order to produce a more effective vaccine. A systematic review of human challenge studies for influenza was performed, with the goal of assessing safety and ethics and determining how these studies have led to therapeutic and vaccine development. A systematic review of systems biology approaches for the study of influenza was also performed, with a focus on how this technology has been utilized for influenza vaccine development. Methods: The PubMed database was searched for influenza human challenge studies, and for systems biology studies that have addressed both influenza infection and immunological effects of vaccination. Results: Influenza human challenge studies have led to important advancements in therapeutics and influenza immunization, and can be performed safely and ethically if certain criteria are met. Many studies have investigated the use of systems biology for evaluating immune response to influenza vaccine, and several promising molecular signatures may help advance our understanding of pathogenesis and be used as targets for influenza interventions. Combining these methodologies has the potential to lead to significant advances in the field of influenza vaccinology and therapeutics. Conclusions: Human challenge studies and systems biology approaches are important tools that should be used in concert to advance our understanding of influenza infection and provide targets for novel therapeutics and immunizations.

Exploration of the Sialic Acid World

Sialic acids are cytoprotectors, mainly localized on the surface of cell membranes with multiple and outstanding cell biological functions. The history of their structural analysis, occurrence, and functions is fascinating and described in this review. Reports from different researchers on apparently similar substances from a variety of biological materials led to the identification of a 9-carbon monosaccharide, which in 1957 was designated "sialic acid." The most frequently occurring member of the sialic acid family is N-acetylneuraminic acid, followed by N-glycolylneuraminic acid and O-acetylated derivatives, and up to now over about 80 neuraminic acid derivatives have been described. They appeared first in the animal kingdom, ranging from echinoderms up to higher animals, in many microorganisms, and are also expressed in insects, but are absent in higher plants. Sialic acids are masks and ligands and play as such dual roles in biology. Their involvement in immunology and tumor biology, as well as in hereditary diseases, cannot be underestimated. N-Glycolylneuraminic acid is very special, as this sugar cannot be expressed by humans, but is a xenoantigen with pathogenetic potential. Sialidases (neuraminidases), which liberate sialic acids from cellular compounds, had been known from very early on from studies with influenza viruses. Sialyltransferases, which are responsible for the sialylation of glycans and elongation of polysialic acids, are studied because of their significance in development and, for instance, in cancer. As more information about the functions in health and disease is acquired, the use of sialic acids in the treatment of diseases is also envisaged.

A Lateral Flow Immunochromato-graphic Strip Test for Rapid Detection of Oseltamivir Phosphate in Egg and Chicken Meat

A lateral flow immunochromatographic strip test (LFIST) based on a competitive format was developed for rapid and sensitive on-site detection of oseltamivir phosphate (OP) residues in poultry product. The sensitivity (half inhibitory concentration, IC₅₀) of the LFIST in the detection of egg and chicken meat samples was confirmed to be 2.56 and 2.63 µg/kg, and the limit detection (LOD) value were 0.43 and 0.42 µg/kg, respectively. For intra-assay and inter-assay reproducibility, recoveries of OP spiked samples ranged between 82.8% and 91.2% with coefficients of variations (CV) less than 5.67% (intra-assay) and 6.52% (inter-assay). The performance of LFIST was comparable to high-performance liquid chromatography (HPLC) in a parallel testing of egg samples and chicken samples. LFIST takes less than 5 minutes, eliminates the dependency on professional personnel, and thus can be used as a surveillance tool for on-site detection of OP residues.

Zoonotic Potential of Influenza A Viruses: A Comprehensive Overview

Influenza A viruses (IAVs) possess a great zoonotic potential as they are able to infect different avian and mammalian animal hosts, from which they can be transmitted to humans. This is based on the ability of IAV to gradually change their genome by mutation or even reassemble their genome segments during co-infection of the host cell with different IAV strains, resulting in a high genetic diversity. Variants of circulating or newly emerging IAVs continue to trigger global health threats annually for both humans and animals. Here, we provide an introduction on IAVs, highlighting the mechanisms of viral evolution, the host spectrum, and the animal/human interface. Pathogenicity determinants of IAVs in mammals, with special emphasis on newly emerging IAVs with pandemic potential, are discussed. Finally, an overview is provided on various approaches for the prevention of human IAV infections.

Antivirals for influenza-Like Illness? A randomised Controlled trial of Clinical and Cost effectiveness in primary CarE (ALIC4 E): the ALIC4 E protocol

INTRODUCTION

Effective management of seasonal and pandemic influenza is a high priority internationally. Guidelines in many countries recommend antiviral treatment for older people and individuals with comorbidity at increased risk of complications. However, antivirals are not often prescribed in primary care in Europe, partly because its clinical and cost effectiveness has been insufficiently demonstrated by non-industry funded and pragmatic studies.

METHODS AND ANALYSIS

Antivirals for influenza-Like Illness? An rCt of Clinical and Cost effectiveness in primary CarE is a European multinational, multicentre, open-labelled, non-industry funded, pragmatic, adaptive-platform, randomised controlled trial. Initial trial arms will be best usual primary care and best usual primary care plus treatment with oseltamivir for 5 days. We aim to recruit at least 2500 participants ≥1 year presenting with influenza-like illness (ILI), with symptom duration ≤72 hours in primary care over three consecutive periods of confirmed high influenza incidence. Participant outcomes will be followed up to 28 days by diary and telephone. The primary objective is to determine whether adding antiviral treatment to best usual primary care is effective in reducing time to return to usual daily activity with fever, headache and muscle ache reduced to minor severity or less. Secondary objectives include estimating cost-effectiveness, benefits in subgroups according to age (<12, 12-64 and >64 years), severity of symptoms at presentation (low, medium and high), comorbidity (yes/no), duration of symptoms (≤48 hours/>48-72 hours), complications (hospital admission and pneumonia), use of additional prescribed medication including antibiotics, use of over-the-counter medicines and self-management of ILI symptoms.

ETHICS AND DISSEMINATION

Research ethics committee (REC) approval was granted by the NRES Committee South Central (Oxford B) and Clinical Trial Authority (CTA) approval by The Medicines and Healthcare products Regulatory Agency. All participating countries gained national REC and CTA approval as required. Dissemination of results will be through peer-reviewed scientific journals and conference presentations.

TRIAL REGISTRATION NUMBER

ISRCTN27908921; Pre-results.

Influenza burden, prevention, and treatment in asthma-A scoping review by the EAACI Influenza in asthma task force

To address uncertainties in the prevention and management of influenza in people with asthma, we performed a scoping review of the published literature on influenza burden; current vaccine recommendations; vaccination coverage; immunogenicity, efficacy, effectiveness, and safety of influenza vaccines; and the benefits of antiviral drugs in people with asthma. We found significant variation in the reported rates of influenza detection in individuals with acute asthma exacerbations making it unclear to what degree influenza causes exacerbations of underlying asthma. The strongest evidence of an association was seen in studies of children. Countries in the European Union currently recommend influenza vaccination of adults with asthma; however, coverage varied between regions. Coverage was lower among children with asthma. Limited data suggest that good seroprotection and seroconversion can be achieved in both children and adults with asthma and that vaccination confers a degree of protection against influenza illness and asthma-related morbidity to children with asthma. There were insufficient data to determine efficacy in adults. Overall, influenza vaccines appeared to be safe for people with asthma. We identify knowledge gaps and make recommendations on future research needs in relation to influenza in patients with asthma.

Reactivity and sensitivity of commercially available influenza rapid diagnostic tests in Japan

Seasonal influenza virus routinely causes epidemic infections throughout the world. Sporadic infections by H5N1, H5N6, and H7N9 viruses are also reported. To treat patients suffering from such viral infections, broadly reactive and highly sensitive influenza rapid diagnostic tests (IRDTs) are required. Here, we examined the reactivity and sensitivity of 25 IRDTs available in Japan for the detection of seasonal H1N1pdm09, H3N2, and type B viruses, as well as highly pathogenic H5 and H7 viruses. All of the IRDTs tested detected the seasonal viruses and H5 and H7 viruses albeit with different sensitivities. Several IRDTs detected the H5 and H7 viruses and the seasonal viruses with similar (high) sensitivity.

Pulmonary immunity to viruses

Mucosal surfaces, such as the respiratory epithelium, are directly exposed to the external environment and therefore, are highly susceptible to viral infection. As a result, the respiratory tract has evolved a variety of innate and adaptive immune defenses in order to prevent viral infection or promote the rapid destruction of infected cells and facilitate the clearance of the infecting virus. Successful adaptive immune responses often lead to a functional state of immune memory, in which memory lymphocytes and circulating antibodies entirely prevent or lessen the severity of subsequent infections with the same virus. This is also the goal of vaccination, although it is difficult to vaccinate in a way that mimics respiratory infection. Consequently, some vaccines lead to robust systemic immune responses, but relatively poor mucosal immune responses that protect the respiratory tract. In addition, adaptive immunity is not without its drawbacks, as overly robust inflammatory responses may lead to lung damage and impair gas exchange or exacerbate other conditions, such as asthma or chronic obstructive pulmonary disease (COPD). Thus, immune responses to respiratory viral infections must be strong enough to eliminate infection, but also have mechanisms to limit damage and promote tissue repair in order to maintain pulmonary homeostasis. Here, we will discuss the components of the adaptive immune system that defend the host against respiratory viral infections.

Drug generations that combat influenza A virus infection

Influenza viruses are significant human respiratory pathogens that cause infections and unpredictable pandemic outbreaks. M2 ion-channel protein, participating in the transmission of viral genetic materials into infected cells, is considered to be the crucial target for old-generation drugs such as rimantadine and amantadine. Neuraminidase protein, which is responsible for the replication of the influenza virus, is affected by the new generation of drugs, including oseltamivir (Tamiflu) and zanamivir (Relenza). The virus mutations that cause oseltamivir resistance are also described. This review presents the details concerning the treatment of influenza neuraminidase inhibitors against the H5N1 strain. It also describes virus mutations that cause resistance to oseltamivir and presents a new drug, peramivir, which is a neuraminidase inhibitor that was introduced against the H1N1 epidemic. This work specifies the details of the pharmacokinetics, dosing, toxicity, side effects, and efficiency of the drugs being used against influenza A virus infections.

Oseltamivir PK/PD Modeling and Simulation to Evaluate Treatment Strategies against Influenza-Pneumococcus Coinfection

Influenza pandemics and seasonal outbreaks have shown the potential of Influenza A virus (IAV) to enhance susceptibility to a secondary infection with the bacterial pathogen Streptococcus pneumoniae (Sp). The high morbidity and mortality rate revealed the poor efficacy of antiviral drugs and vaccines to fight IAV infections. Currently, the most effective treatment for IAV is by antiviral neuraminidase inhibitors. Among them, the most frequently stockpiled is Oseltamivir which reduces viral release and transmission. However, effectiveness of Oseltamivir is compromised by the emergence of resistant IAV strains and secondary bacterial infections. To date, little attention has been given to evaluate how Oseltamivir treatment strategies alter Influenza viral infection in presence of Sp coinfection and a resistant IAV strain emergence. In this paper we investigate the efficacy of current approved Oseltamivir treatment regimens using a computational approach. Our numerical results suggest that the curative regimen (75 mg) may yield 47% of antiviral efficacy and 9% of antibacterial efficacy. An increment in dose to 150 mg (pandemic regimen) may increase the antiviral efficacy to 49% and the antibacterial efficacy to 16%. The choice to decrease the intake frequency to once per day is not recommended due to a significant reduction in both antiviral and antibacterial efficacy. We also observe that the treatment duration of 10 days may not provide a clear improvement on the antiviral and antibacterial efficacy compared to 5 days. All together, our in silico study reveals the success and pitfalls of Oseltamivir treatment strategies within IAV-Sp coinfection and calls for testing the validity in clinical trials.

Virus-induced secondary bacterial infection: a concise review

Respiratory diseases are a very common source of morbidity and mortality among children. Health care providers often face a dilemma when encountering a febrile infant or child with respiratory tract infection. The reason expressed by many clinicians is the trouble to confirm whether the fever is caused by a virus or a bacterium. The aim of this review is to update the current evidence on the virus-induced bacterial infection. We present several clinical as well in vitro studies that support the correlation between virus and secondary bacterial infections. In addition, we discuss the pathophysiology and prevention modes of the virus–bacterium coexistence. A search of the PubMed and MEDLINE databases was carried out for published articles covering bacterial infections associated with respiratory viruses. This review should provide clinicians with a comprehensive idea of the range of bacterial and viral coinfections or secondary infections that could present with viral respiratory illness.

Structural and computational study on inhibitory compounds for endonuclease activity of influenza virus polymerase

Seasonal epidemics and occasional pandemics caused by influenza viruses are global threats to humans. Since the efficacy of currently approved drugs is limited by the emerging resistance of the viruses, the development of new antiviral drugs is still demanded. Endonuclease activity, which lies in the influenza polymerase acidic protein N-terminal domain (PA(N)), is a potent target for novel antiviral agents. Here, we report the identification of some novel inhibitors for PA(N) endonuclease activity. The binding mode of one of the inhibitory compounds to PA(N) was investigated in detail by means of X-ray crystal structure analysis and molecular dynamics (MD) simulation. It was observed in the crystal structure that three molecules of the same kind of inhibitor were bound to one PA(N). One of the three molecules is located at the active site and makes a chelation to metal ions. Another molecule is positioned at the space adjacent to the metal-chelated site. The other molecule is located at a site slightly apart from the metal-chelated site, causing a conformational change of Arg124. The last binding site was not observed in previous crystallographic studies. Hence, the stability of inhibitor binding was examined by performing 100-ns MD simulation. During the MD simulation, the three inhibitor molecules fluctuated at the respective binding sites at different amplitudes, while all of the molecules maintained interactions with the protein. Molecular mechanics/generalized Born surface area (MM/GBSA) analysis suggested that the molecule in the last binding site has a higher affinity than the others. Structural information obtained in this study will provide a hint for designing and developing novel potent agents against influenza viruses.

Zanamivir Amidoxime- and N-Hydroxyguanidine-Based Prodrug Approaches to Tackle Poor Oral Bioavailability

The neuraminidase (NA) inhibitor zanamivir (1) is potently active against a broad panel of influenza A and B strains, including mutant viruses, but suffers from pharmacokinetic (PK) shortcomings. Here, distinct prodrug approaches are described that aimed at overcoming zanamivir's lack of oral bioavailability. Lowering the high basicity of the 4-guanidino group in zanamivir and of a bioisosteric 4-acetamidine analog (5) by N-hydroxylation was deemed to be a plausible tactic. The carboxylic acid and glycerol side chain were also masked with different ester groups. The bioisosteric amidine 5 turned out to be potently active against a panel of H1N1 (IC50 = 2-10 nM) and H3N2 (IC50 = 5-10 nM) influenza A viruses (NA inhibition assay). In vitro PK studies showed that all prodrugs were highly soluble, exhibited low protein binding, and were bioactivated by N-reduction to the respective guanidines and amidines. The most promising prodrug candidates, amidoxime ester 7 and N-hydroxyguanidine ester 8, were subjected to in vivo bioavailability studies. Unfortunately, both prodrugs were not orally bioavailable to a convincing degree (F ≤ 3.7%, rats). This finding questions the general feasibility of improving the oral bioavailability of 1 by lipophilicity-increasing prodrug strategies, and suggests that intrinsic structural features represent key hurdles.

Impact of time to treatment of oseltamivir on influenza hospitalization cost among Korean children

BACKGROUND

Although oseltamivir is a common influenza treatment, there is a lack of data on the economic benefits of timely oseltamivir treatment.

METHODS

From February 2004 through June 2007, 116 hospitalized children ≤ 15 years of age with laboratory-confirmed influenza who received oseltamivir were identified via retrospective medical chart review. Demographic, clinical, and cost data were abstracted and multivariate linear regression was used to assess the association between oseltamivir time to treatment and treatment-related costs among hospitalized children with laboratory-confirmed influenza.

RESULTS

Overall, 28% (n = 33) of patients were treated with oseltamivir ≥ day 3 of admission. Rapid influenza diagnostic test was used in a significantly lower proportion of patients treated with oseltamivir ≥ day 3 of admission compared with those who received oseltamivir earlier. On multivariate linear regression, initiation of oseltamivir ≥ day 3 of admission was associated with a 60.84% increase (95%CI: 32.59-95.11) in treatment-related hospital costs, compared with initiation on admission.

CONCLUSION

Delayed initiation of oseltamivir was found to be associated with increased treatment-related hospital costs among children hospitalized with laboratory-confirmed influenza.

Detection sensitivity of influenza rapid diagnostic tests

The sensitivity of influenza rapid diagnostic tests (IRDTs) currently available in Japan for various influenza virus strains, including human H7N9 and H5N1 isolates, were compared and it was found that all of the IRDTs examined detected these viruses; however, their detection sensitivities differed.

Antiviral treatment of influenza in South Korea

Antiviral therapy has an important role in the treatment and chemoprophylaxis of influenza. At present, two classes of antiviral agents, adamantanes and neuraminidase inhibitors, are available for the treatment and chemoprophylaxis of influenza in Korea. Because of the widespread resistance against adamantanes, neuraminidase inhibitors are mainly used. Because each country has a unique epidemiology of influenza, the proper use of antiviral agents should be determined based on local data. Decisions on the clinical practice in the treatment of influenza in South Korea are guided by the local surveillance data, practice guidelines, health insurance system and the resistance patterns of the circulating influenza viruses. This review highlights the role of antiviral agents in the treatment and outcome of influenza in Korea by providing comprehensive information of their clinical usage in Korea.

Published sequences do not support transfer of oseltamivir resistance mutations from avian to human influenza A virus strains

Background

Tamiflu (oseltamivir phosphate ester, OE) is a widely used antiviral active against influenza A virus. Its active metabolite, oseltamivir carboxylate (OC), is chemically stable and secreted into wastewater treatment plants. OC contamination of natural habitats of waterfowl might induce OC resistance in influenza viruses persistently infecting waterfowl, and lead to transfer of OC-resistance from avian to human influenza. The aim of this study was to evaluate whether such has occurred.

Methods

A genomics approach including phylogenetic analysis and probability calculations for homologous recombination was applied on altogether 19,755 neuraminidase (N1 and N2) genes from virus sampled in humans and birds, with and without resistance mutations.

Results

No evidence for transfer of OE resistance mutations from avian to human N genes was obtained, and events suggesting recombination between human and avian influenza virus variants could not be traced in the sequence material studied.

Conclusions

The results indicate that resistance in influenza viruses infecting humans is due to the selection pressure posed by the global OE administration in humans rather than transfer from avian influenza A virus strains carrying mutations induced by environmental exposure to OC.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-015-0860-9) contains supplementary material, which is available to authorized users.

Survey of compliance with oseltamivir phosphate therapy in Japan

Oseltamivir phosphate, which is available in oral formulation, is effective for type A/B influenza virus infection. In Japan, drug-induced adverse reactions such as central nervous system symptoms are a concern, especially in children. In this survey, we implemented a questionnaire regarding the administration period described on prescriptions and the duration for which patients took the drug, to investigate compliance with oseltamivir phosphate therapy. The results showed that therapy with oseltamivir phosphate was discontinued by 21.1%. The main reasons for discontinuation were the relief of symptoms and appearance of adverse reactions. This survey revealed that some patients taking oseltamivir phosphate would like to be prescribed medication for as short a term as possible. Although it is recommended that oseltamivir phosphate be administered for 5 days to treat influenza symptoms, 3- or 4-day administration was frequently prescribed for young patients (aged <20 years) and children. Because the appropriate administration period for influenza treatment is unclear, further epidemiological data are needed to determine the most rational use of neuraminidase inhibitors for influenza treatment.

Insight into alternative approaches for control of avian influenza in poultry, with emphasis on highly pathogenic H5N1

Highly pathogenic avian influenza virus (HPAIV) of subtype H5N1 causes a devastating disease in poultry but when it accidentally infects humans it can cause death. Therefore, decrease the incidence of H5N1 in humans needs to focus on prevention and control of poultry infections. Conventional control strategies in poultry based on surveillance, stamping out, movement restriction and enforcement of biosecurity measures did not prevent the virus spreading, particularly in developing countries. Several challenges limit efficiency of the vaccines to prevent outbreaks of HPAIV H5N1 in endemic countries. Alternative and complementary approaches to reduce the current burden of H5N1 epidemics in poultry should be encouraged. The use of antiviral chemotherapy and natural compounds, avian-cytokines, RNA interference, genetic breeding and/or development of transgenic poultry warrant further evaluation as integrated intervention strategies for control of HPAIV H5N1 in poultry.

Inhibitory influence of the hexapeptidic sequence SLIGRL on influenza A virus infection in mice

Proteinase-activated receptor 2 (PAR(2)) is widely expressed in the respiratory tract and is an integral component of the host antimicrobial defense system. The principal aim of this study was to investigate the influence of a PAR(2)-activating peptide, SLIGRL, on influenza A virus (IAV)-induced pathogenesis in mice. Intranasal inoculation of BALB/c mice with influenza A/PR/8/34 virus caused time-dependent increases in the number of pulmonary leukocytes (recovered from bronchoalveolar lavage fluid), marked airway histopathology characterized by extensive epithelial cell damage, airway hyper-responsiveness to the bronchoconstrictor methacholine, and elevated levels of inflammatory chemokines (keratinocyte-derived chemokine and macrophage inflammatory protein 2) and cytokines (interferon-γ). It is noteworthy that these IAV-induced effects were dose-dependently attenuated in mice treated with a PAR(2)-activating peptide, SLIGRL, at the time of IAV inoculation. However, SLIGRL also inhibited IAV-induced increases in pulmonary leukocytes in PAR(2)-deficient mice, indicating these antiviral actions were not mediated by PAR(2). The potency order obtained for a series of structural analogs of SLIGRL for anti-IAV activity (IGRL > SLIGRL > LSIGRL >2-furoyl-LIGRL) was also inconsistent with a PAR(2)-mediated effect. In further mechanistic studies, SLIGRL inhibited IAV-induced propagation in ex vivo perfused segments of trachea from wild-type or PAR(2)(-/-) mice, but did not inhibit viral attachment or replication in Madin-Darby canine kidney cells and chorioallantoic membrane cells, which are established hosts for IAV. In summary, SLIGRL protected mice from IAV infection independently of PAR(2) and independently of direct inhibition of IAV attachment or replication, potentially through the activation of endogenous antiviral pathways within the mouse respiratory tract.

Mechanism of drug resistance of hemagglutinin of influenza virus and potent scaffolds inhibiting its function

Highly pathogenic influenza viruses have become a global threat to humans. It is important to select an effective therapeutic option suitable for the subtypes in an epidemic or pandemic. To increase the options, the development of novel antiviral agents acting on targets different from those of the currently approved drugs is required. In this study, we performed molecular dynamics simulations on a spike protein on the viral envelop, hemagglutinin, for the wild-type and three kinds of mutants using a model system consisting of a trimeric hemagglutinin complex, viral lipid membrane, solvation waters, and ions. A natural product, stachyflin, which shows a high level of antiviral activity specific to some subtypes of influenza viruses, was examined on binding to the wild-type hemagglutinin by docking simulation. The compound potency of stachyflin is, however, easily lost due to resistant mutations. From a comparison of simulation results between the wild-type and the resistant mutants, the reason for the drug resistance of hemagglutinin was clarified. Next, 8 compounds were selected from a chemical database by in silico screening, considering the findings from the simulations. Inhibitory activities to suppress the proliferation of influenza virus were measured by cell-based antiviral assays, and two chemical scaffolds were found to be potent for an inhibitor. More than 30 derivatives bearing either of these two chemical scaffolds were synthesized, and cell culture assays were carried out to evaluate the compound potency. Several derivatives displayed a high compound potency, and 50% effective concentrations of two synthesized compounds were below 1 μM.

Adverse drug reaction profile of oseltamivir in children

AIM

To monitor and evaluate the pattern of ADRs to oseltamivir in pediatric population suffering from H1N1 influenza at a tertiary care hospital.

MATERIALS AND METHODS

Children offered oseltamivir for treatment and chemoprophylaxis were monitored for adverse events by direct questioning for symptoms and clinical examination on day 5 and day 10. Assessment of neurological events was done by asking the parents or guardians regarding development of specific symptoms. Adverse events obtained were analyzed for severity, causality and age-group wise.

RESULTS

Out of 191 children (median age, 3 years), 69 (36.1%) developed ADRs. Most common symptoms were vomiting (16.2%) followed by diarrhea (12.0%), ear disorders (8.9%), and insomnia (6.8%). The incidence of neuropsychiatric symptoms was 12.6% which were mild-to-moderate on severity scale. There was no significant difference in the incidence of adverse events between children less than 1 year and other age groups.

CONCLUSION

Oseltamivir is well tolerated in Indian children with suspected or confirmed H1N1 influenza. Our study also indicates safety of oseltamivir in infants.

Prospects for controlling future pandemics of influenza

Pandemic influenza remains one of the most serious threats to global public health and continued global vigilance to monitor emerging threats is crucial. Of the weapons available to control a pandemic, vaccination is potentially the most powerful, but there are currently serious limitations to timely availability of vaccine supply in an emergency. Many novel influenza vaccines are in development, some of which have the potential to deliver the massive quantities of vaccine that would be required in a pandemic in a short period of time. However, for the foreseeable future, it is likely that the principal vaccine that will be deployed in a pandemic will be an inactivated egg-derived vaccine of the kind that has been available for several decades. This review will focus on the practical hurdles that need to be surmounted to deliver large amounts of safe and effective pandemic vaccine to the general public. There needs to be a continued focus on improvement to the vaccine response system that will require close collaboration between influenza and vaccine experts, manufacturers, regulators and public health authorities around the world.

Oseltamivir in seasonal, avian H5N1 and pandemic 2009 A/H1N1 influenza: pharmacokinetic and pharmacodynamic characteristics

Oseltamivir is the ester-type prodrug of the neuraminidase inhibitor oseltamivir carboxylate. It has been shown to be an effective treatment for both seasonal influenza and the recent pandemic 2009 A/H1N1 influenza, reducing both the duration and severity of the illness. It is also effective when used preventively. This review aims to describe the current knowledge of the pharmacokinetic and pharmacodynamic characteristics of this agent, and to address the issue of possible therapeutic drug monitoring. According to the currently available literature, the pharmacokinetics of oseltamivir carboxylate after oral administration of oseltamivir are characterized by mean ± SD bioavailability of 79 ± 12%, apparent clearance of 25.3 ± 7.0 L/h, an elimination half-life of 7.4 ± 2.5 hours and an apparent terminal volume of distribution of 267 ± 122 L. A maximum plasma concentration of 342 ± 83 μg/L, a time to reach the maximum plasma concentration of 4.2 ± 1.1 hours, a trough plasma concentration of 168 ± 32 μg/L and an area under the plasma concentration-time curve from 0 to 24 hours of 6110 ± 1330 μg · h/L for a 75 mg twice-daily regimen were derived from literature data. The apparent clearance is highly correlated with renal function, hence the dosage needs to be adjusted in proportion to the glomerular filtration rate. Interpatient variability is moderate (28% in apparent clearance and 46% in the apparent central volume of distribution); there is no indication of significant erratic or limited absorption in given patient subgroups. The in vitro pharmacodynamics of oseltamivir carboxylate reveal wide variation in the concentration producing 50% inhibition of influenza A and B strains (range 0.17-44 μg/L). A formal correlation between systemic exposure to oseltamivir carboxylate and clinical antiviral activity or tolerance in influenza patients has not yet been demonstrated; thus no formal therapeutic or toxic range can be proposed. The pharmacokinetic parameters of oseltamivir carboxylate after oseltamivir administration (bioavailability, apparent clearance and the volume of distribution) are fairly predictable in healthy subjects, with little interpatient variability outside the effect of renal function in all patients and bodyweight in children. Thus oseltamivir carboxylate exposure can probably be controlled with sufficient accuracy by thorough dosage adjustment according to patient characteristics. However, there is a lack of clinical study data on naturally infected patients. In addition, the therapeutic margin of oseltamivir carboxylate is poorly defined. The usefulness of systematic therapeutic drug monitoring in patients therefore appears to be questionable; however, studies are still needed to extend the knowledge to particular subgroups of patients or dosage regimens.

Seasonal, avian, and novel H1N1 influenza: prevention and treatment modalities

OBJECTIVE

To review the pathophysiology, pandemics/epidemics, transmissibility, clinical presentation, treatment, prevention/immunization, and resistance associated with seasonal, avian, and swine influenza.

DATA SOURCES

Literature was obtained from MEDLINE (1966-October 2009) and International Pharmaceutical Abstracts (1971-October 2009) using the search terms influenza, seasonal influenza, avian influenza, swine influenza, H1N1, novel H1N1, H3N2, and H5N1.

STUDY SELECTION AND DATA EXTRACTION

Available English-language articles were reviewed, along with information obtained from the Centers for Disease Control and Prevention, the Food and Drug Administration, and the World Health Organization.

DATA SYNTHESIS

The influenza virus has caused disease in birds, swine, and humans for many centuries. Pandemics and epidemics have occurred throughout history and reports of new strains continue to emerge. Two major surface antigenic glycoproteins, hemagglutinin and neuraminidase, have various subtypes, resulting in numerous combinations of these proteins. For example, combinations occur when an influenza strain from a bird "mixes" with a strain from a human. This mixing occurs in a host, often in pigs, resulting in a new strain. This new strain can cause pandemics since people have no immunity to the new strain. An H1N1 subtype pandemic occurred in 1918, causing millions of deaths. Simultaneously, veterinary reports of "influenza" in pigs also emerged. It is postulated that humans infected pigs with this H1N1 virus. H1N1 reappeared in humans in 1976, and more recently in 2009. Other pandemics have occurred with H2N2 and H3N2 strains. In 1997, strain H5N1, which usually causes disease in fowl, was able to infect humans.

CONCLUSIONS

Influenza subtypes continue to change, causing disease in animals and humans. Utilization of immunization and antiviral treatment options are available to prevent, treat, and contain the spread of this infection.