Oseltamivir in the management of influenza

Preparation of eicosavalent triazolylsialoside-conjugated human serum albumin as a dual hemagglutinin/neuraminidase inhibitor and virion adsorbent for the prevention of influenza infection

A triazolylsialoside-human serum albumin conjugate was prepared as a multivalent hemagglutinin and neuraminidase inhibitor using a di-(N-succinimidyl) adipate strategy. Matrix-Assisted Laser Desorption/Ionization-Time of Flight-Mass Spectrometry (MALDI-TOF-MS) indicated that five tetravalent sialyl galactosides were grafted onto the protein backbone resulting in an eicosavalent triazolylsialoside-protein complex. Compared with monomeric sialic acid, molecular interaction studies showed that the synthetic pseudo-glycoprotein bound tightly not only to hemagglutinin (HA)/neuraminidase (NA) but also to mutated drug-resistant NA on the surface of the influenza virus with a dissociation constant (KD) in the 1 μM range, attributed to the cluster effect. Moreover, this glycoconjugate exhibited potent antiviral activity against a broad spectrum of virus strains and showed no cytotoxicity towards Human Umbilical Vein Endothelial Cells (HUVECs) and Madin-Darby canine kidney (MDCK) cells at high concentrations. Further mechanistic studies demonstrated this multivalent sialyl conjugate showed strong capture and trapping of influenza virions, thus disrupting the ability of the influenza virus to infect host cells. This research lays the experimental foundation for the development of new antiviral agents based on multivalent sialic acid-protein conjugates.

Structure and Role of O-Linked Glycans in Viral Envelope Proteins

N- and O-glycans are both important constituents of viral envelope glycoproteins. O-linked glycosylation can be initiated by any of 20 different human polypeptide O-acetylgalactosaminyl transferases, resulting in an important functional O-glycan heterogeneity. O-glycans are organized as solitary glycans or in clusters of multiple glycans forming mucin-like domains. They are functional both in the viral life cycle and in viral colonization of their host. Negatively charged O-glycans are crucial for the interactions between glycosaminoglycan-binding viruses and their host. A novel mechanism, based on controlled electrostatic repulsion, explains how such viruses solve the conflict between optimized viral attachment to target cells and efficient egress of progeny virus. Conserved solitary O-glycans appear important for viral uptake in target cells by contributing to viral envelope fusion. Dual roles of viral O-glycans in the host B cell immune response, either epitope blocking or epitope promoting, may be exploitable for vaccine development. Finally, specific virus-induced O-glycans may be involved in viremic spread.

Prodrug approach: An overview of recent cases

In this review we highlight the most modern trends in the prodrug strategy. In drug research and development, the prodrug concept has found a number of useful applications. Selected examples of this approach are provided in this paper and they are classified according to the aim of their design.

Pharmacokinetic/pharmacodynamic modelling approaches in paediatric infectious diseases and immunology

Pharmacokinetic/pharmacodynamic (PKPD) modelling is used to describe and quantify dose-concentration-effect relationships. Within paediatric studies in infectious diseases and immunology these methods are often applied to developing guidance on appropriate dosing. In this paper, an introduction to the field of PKPD modelling is given, followed by a review of the PKPD studies that have been undertaken in paediatric infectious diseases and immunology. The main focus is on identifying the methodological approaches used to define the PKPD relationship in these studies. The major findings were that most studies of infectious diseases have developed a PK model and then used simulations to define a dose recommendation based on a pre-defined PD target, which may have been defined in adults or in vitro. For immunological studies much of the modelling has focused on either PK or PD, and since multiple drugs are usually used, delineating the relative contributions of each is challenging. The use of dynamical modelling of in vitro antibacterial studies, and paediatric HIV mechanistic PD models linked with the PK of all drugs, are emerging methods that should enhance PKPD-based recommendations in the future.

Oseltamivir pharmacokinetics and clinical experience in neonates and infants during an outbreak of H1N1 influenza A virus infection in a neonatal intensive care unit

Detailed oseltamivir pharmacokinetics have yet to be reported in neonates and infants; this group is at high risk of serious influenza-associated complications. Extrapolation of doses from older patients is complicated by rapid organ and drug-metabolizing enzyme maturation. A pharmacokinetic study has been conducted during an influenza A(H1N1) outbreak in a neonatal intensive care unit. Each included patient provided 4 samples for oseltamivir and 4 samples for its active metabolite oseltamivir carboxylate. A population pharmacokinetic model was developed with NONMEM. Allometric weight scaling and maturation functions were added a priori to scale for size and age based on literature values. Nine neonates and infants were recruited. A physiologically parameterized pharmacokinetic model predicted typical day 1 area under the curve (AUC(0-12)) values of 1,966 and 2,484 μg · h/liter for neonates and infants of ≤ 37 weeks of postmenstrual age (PMA) and >37 weeks of PMA treated with 1 mg/kg of body weight and 2 mg/kg, respectively. The corresponding steady-state AUC(0-12) values were 3,670 and 4,559 μg · h/liter. Premature neonates treated with 1 mg/kg and term babies treated with 2 mg/kg should have average oseltamivir carboxylate concentrations in a range similar to that for adults treated with 75 mg, corresponding to >200-fold above the half-maximal inhibitory concentration (IC(50)) value for influenza A(H1N1) from the start of therapy.

The 2008-2009 H1N1 influenza virus exhibits reduced susceptibility to antibody inhibition: Implications for the prevalence of oseltamivir resistant variant viruses

A naturally-occurring H275Y oseltamivir resistant variant of influenza A (H1N1) virus emerged in 2007, subsequently becoming prevalent worldwide, via an undetermined mechanism. To understand the antigenic properties of the H275Y variant, oseltamivir resistant and susceptible strains of H1N1 viruses were analyzed by hemagglutination inhibition (HI) and microneutralization assays. HI analysis with H1-positive sera obtained from seasonal flu vaccine immunized and non-immunized individuals, and H1-specific monoclonal antibodies, revealed that resistant strains exhibited a reduced reactivity to these antisera and antibodies in the HI assay, as compared to susceptible strains. Neutralization assay testing demonstrated that oseltamivir resistant H1N1 strains are also less susceptible to antibody inhibition during infection. Mice inoculated with a resistant clinical isolate exhibit 4-fold lower virus-specific antibody titers than mice infected with a susceptible strain under the same conditions. Resistant and sensitive variants of 2009 pandemic H1N1 virus did not exhibit such differences. While HA1 and NA phylogenetic trees show that both oseltamivir resistant and susceptible strains belong to clade 2B, NA D354G and HA A189T substitutions were found exclusively, and universally, in oseltamivir resistant variants. Our results suggest that the reduced susceptibility to antibody inhibition and lesser in vivo immunogenicity of the oseltamivir resistant 2008-2009 H1N1 influenza A virus is conferred by coupled NA and HA mutations, and may contribute to the prevalence of this H1N1 variant.

Influenza pharmacotherapy: present situation, strategies and hopes

INTRODUCTION

Influenza is a serious health threat for people of all ages. The causative virus is evolving continuously and the risk of an unexpected mutant, which cannot be controlled by seasonal vaccination, is real. New and more effective antiviral drugs are needed.

AREAS COVERED

This review examines the antiviral drugs with confirmed efficacy in combating influenza, as well as newer compounds that are currently undergoing testing and will hopefully be marketed in the near future. A comprehensive, state-of-the-art picture of drug therapy for influenza is presented, including novel solutions and effective strategies for prescribing currently available antiviral drugs, with emphasis on the importance of updated local epidemiological data, clinical assessment and laboratory testing.

EXPERT OPINION

Current anti-influenza drug research is no longer tied solely to viral envelope protein targets like haemagglutinin and neuraminidase. New drugs act on the viral RNA polymerase complex, which is involved in transcription and replication of the viral genome, and can prevent the maturation, replication and dissemination of numerous viral subtypes. Combating this infection and reducing the duration of symptoms also has important socioeconomic implications related to health-care spending (including hospitalization for complications) and sick-leave pay for workers.

Interaction between influenza virus and Streptococcus pneumoniae in severe pneumonia

The contribution of bacterial superinfection to influenza-associated pneumonia morbidity and mortality is evident from the 1918 and 1957 influenza pandemics, and is supported by a number of murine model studies. Murine model studies have also assisted in helping to expand our understanding of the pathogenesis of the interaction between the influenza virus and subsequent susceptibility to pneumococcal superinfections. The purported impact that the pneumococcal conjugate vaccine has had on reducing the burden of confirmed influenza-associated pneumonia, as well as upon all-cause clinical pneumonia, provides additional clinical evidence of the role of superimposed pneumococcal infections as a cause of severe pneumonia in children. Using this information together with the evidence for the effectiveness of influenza vaccination against influenza-associated pneumonia, it is imperative that preventive strategies for future influenza pandemic preparedness include broad-based vaccination against pneumococci, as well as ensuring that adequate antimicrobials are available for the early treatment of influenza virus, in addition to pneumococcal and other bacterial infections.

In vitro pharmacological selectivity profile of oseltamivir prodrug (Tamiflu) and active metabolite

Neuropsychiatric adverse events have been reported in influenza patients with and without exposure to oseltamivir (Tamiflu), triggering speculation as to whether oseltamivir may be interacting with any human receptors and contributing to such neuropsychiatric events. In this study, the in vitro selectivity profile of oseltamivir prodrug and active metabolite was investigated. Both compounds lacked clinically relevant pharmacological activities on human, rodent and primate neuraminidases and on a panel of 155 other molecular targets, including those relevant for mood, cognition and behavior. Neuropsychiatric adverse events observed in influenza patients are likely a phenomenon caused by the infection rather than by oseltamivir.

Nonclinical pharmacokinetics of oseltamivir and oseltamivir carboxylate in the central nervous system

Oseltamivir, a potent and selective inhibitor of influenza A and B virus neuraminidases, is a prodrug that is systemically converted into the active metabolite oseltamivir carboxylate. In light of reported neuropsychiatric events in influenza patients, including some taking oseltamivir, and as part of a full assessment to determine whether oseltamivir could contribute to, or exacerbate, such events, we undertook a series of nonclinical studies. In particular, we investigated (i) the distribution of oseltamivir and oseltamivir carboxylate in the central nervous system of rats after single intravenous doses of oseltamivir and oseltamivir carboxylate and oral doses of oseltamivir, (ii) the active transport of oseltamivir and oseltamivir carboxylate in vitro by transporters located in the blood-brain barrier, and (iii) the extent of local conversion of oseltamivir to oseltamivir carboxylate in brain fractions. In all experiments, results showed that the extent of partitioning of oseltamivir and especially oseltamivir carboxylate to the central nervous system was low. Brain-to-plasma exposure ratios were approximately 0.2 for oseltamivir and 0.01 for oseltamivir carboxylate. Apart from oseltamivir being a good substrate for the P-glycoprotein transporter, no other active transport processes were observed. The conversion of the prodrug to the active metabolite was slow and limited in human and rat brain S9 fractions. Overall, these studies indicate that the potential for oseltamivir and oseltamivir carboxylate to reach the central nervous system in high quantities is low and, together with other analyses and studies, that their involvement in neuropsychiatric events in influenza patients is unlikely.

Antivirals for the treatment and prevention of epidemic and pandemic influenza

Influenza is a highly contagious and debilitating disease that imposes an excess burden of complications and mortality. Antiviral therapy is the primary intervention for treatment and post‐exposure prophylaxis (PEP) of influenza. Amantadine and rimantadine are members of the M2 class of antiviral agents and are moderately effective in influenza management. However, their utility is compromised by high levels of resistance, tolerability concerns and a lack of efficacy against influenza B. An alternative class of agents, the neuraminidase inhibitors (NIs), represent the most advanced form of antiviral therapy available, and act by specifically inhibiting the neuraminidase enzymes that are present on all influenza subtypes. Two NIs, oseltamivir and zanamivir, are currently available for clinical use. Oseltamivir, the most widely used NI, is administered orally as a prodrug (oseltamivir carboxylate) and systemically distributed to all potential infection sites. Zanamivir, a second NI, is administered by inhalation via a disk inhaler and deposited primarily in the respiratory tract. When administered within 48 hours of symptom onset, both agents significantly reduce illness duration and symptom severity, and decrease the rate of influenza‐associated complications. With oseltamivir, greater benefits are detected with earlier treatment initiation (<12 hours). In PEP, both NIs effectively protect the close contacts of index cases from symptomatic influenza. Oseltamivir and zanamivir are generally well tolerated and associated with a low level of resistance. Emerging evidence supports the activity of both NIs against the H5N1avian influenza infection, which is a pandemic candidate. However, the WHO currently recommends the use of oseltamivir for the management of suspected cases, given the systemic nature of the H5N1 challenge. Ongoing studies are exploring the effectiveness of oseltamivir, zanamivir and other NIs for pandemic management.

Anti-influenza drugs: the development of sialidase inhibitors

Viruses, particularly those that are harmful to humans, are the 'silent terrorists' of the twenty-first century. Well over four million humans die per annum as a result of viral infections alone. The scourge of influenza virus has plagued mankind throughout the ages. The fact that new viral strains emerge on a regular basis, particularly out of Asia, establishes a continual socio-economic threat to mankind. The arrival of the highly pathogenic avian influenza H5N1 heightened the threat of a potential human pandemic to the point where many countries have put in place 'preparedness plans' to defend against such an outcome. The discovery of the first designer influenza virus sialidase inhibitor and anti-influenza drug Relenza, and subsequently Tamiflu, has now inspired a number of continuing efforts towards the discovery of next generation anti-influenza drugs. Such drugs may act as 'first-line-of-defence' against the spread of influenza infection and buy time for necessary vaccine development particularly in a human pandemic setting. Furthermore, the fact that influenza virus can develop resistance to therapeutics makes these continuing efforts extremely important. An overview of the role of the virus-associated glycoprotein sialidase (neuraminidase) and some of the most recent developments towards the discovery of anti-influenza drugs based on the inhibition of influenza virus sialidase is provided in this chapter.

Population pharmacokinetics of oseltamivir when coadministered with probenecid

Oseltamivir is a potent, selective, oral neuraminidase inhibitor for the treatment and prophylaxis of influenza. Plasma concentrations of the active metabolite, oseltamivir carboxylate, are increased in the presence of probenecid, suggesting that the combination could allow for the use of reduced doses of oseltamivir. To investigate this proposal, we developed a population pharmacokinetic model and simulated the pharmacokinetics of candidate combination regimens of oral oseltamivir (45 mg and 30 mg twice a day) plus oral probenecid (500 mg/6 hourly). Probenecid plus oseltamivir 45 mg achieved all the pharmacokinetic parameters expected of oseltamivir alone, but combination with oseltamivir 30 mg and dose interval extension approaches did not. An oseltamivir-probenecid combination may compromise tolerability and enhance the potential for drug interactions. In addition, increased dosing requirements may affect compliance and attainment of optimal oseltamivir exposure, potentially facilitating the emergence of viral strains with reduced susceptibility to oseltamivir. These factors, set alongside increased capacity for oseltamivir production, should be carefully considered before an oseltamivir-probenecid combination is used.

Neuraminidase inhibitor resistance in influenza viruses

Zanamivir and oseltamivir, the currently marketed influenza virus neuraminidase inhibitors (NAIs), are prescribed for the treatment and prophylaxis of influenza and are being stockpiled for pandemic influenza. Oseltamivir resistance has been reported in up to 2% of patients in clinical trials of oseltamivir and in up to 18% of treated children. There are also reports in at least three patients treated with oseltamivir for influenza A (H5N1) infections. At this stage, there are no reports of resistance occurring to zanamivir in immunocompetent patients. Zanamivir and oseltamivir bind differently at the neuraminidase catalytic site and this contributes to different drug resistance profiles. The magnitude and duration of NAI concentrations at the site of infection are also expected to be important factors and are determined by route and timing of drug administration, dose, and pharmacokinetic differences between patients. In addition, the type, strain, and virulence of the influenza strain and the nature of the immune response all appear to play a role in determining the likelihood of drug resistance arising. The clinical significance of a particular NAI-resistant isolate from a patient is often not clear but virus viability and transmissibility are clearly important characteristics. Early initiation of NAI treatment in suspected cases of influenza is important for maximizing efficacy and minimizing the risk of drug resistance. Higher NAI doses and longer periods of treatment may be required for patients with influenza A (H5N1) infections but further work is needed in this area.

Development and validation of a rapid HPLC method for the determination of oseltamivir phosphate in Tamiflu® and generic versions

Oseltamivir phosphate (OP) is an antiviral drug that is used in the treatment and prophylaxis of both influenza A and influenza B. It is effective against all known influenza viruses than can infect humans, including pandemic influenza viruses and may be the most appropriate antiviral option against avian influenza caused by H5N1 virus. Tamiflu, the registered trademark used under exclusive license by Roche laboratories with OP as active pharmaceutical ingredient, is considered the best treatment for the bird flu disease. A simple, selective, linear, accurate and precise HPLC method was developed and validated for rapid assay of OP aimed to the quality control of Tamiflu capsules and generic versions. Isocratic elution at a flow rate of 1.2 mL/min was employed on a Zorbax CN column (150 mm x 4.6mm; 5 microm) at ambient temperature. The mobile phase consisted of methanol and 0.04 M formic acid pH 3.0 (50:50, v/v). The UV detection wavelength was 226 nm and 20 microL of sample was injected. Sotalol hydrochloride was used as the internal standard (IS). The retention times for OP and IS were 3.40 and 2.25 min, respectively. The method was successfully applied to commercial pharmaceuticals, Tamiflu and generic versions. The proposed method could be applicable for routine analysis of OP and monitoring of the quality of marketed drugs as possibly counterfeit Tamiflu.

[Emerging viral infectious diseases and pregnancy]

Diverses infections émergentes sont rapportées depuis la mise en place d'une surveillance épidémiologique accrue. Ces infections peuvent compromettre le bon déroulement d'une grossesse, en mettant en jeu le pronostic vital maternel ou le développement de l'enfant lors d'une transmission verticale. À travers une revue récente de la littérature, nous rapportons les conséquences de ces virus émergents les plus cités (H5N1, Coronavirus du SRAS, Chikungunya, virus du Nil occidental) et discutons la prise en charge périnatale.

Status presens of antiviral drugs and strategies: Part II: RNA VIRUSES (EXCEPT RETROVIRUSES)

More than 40 compounds have been formally licensed for clinical use as antiviral drugs, and half of these are used for the treatment of HIV infections. The others have been approved for the therapy of herpesvirus (HSV, VZV, CMV), hepadnavirus (HBV), hepacivirus (HCV) and myxovirus (influenza, RSV) infections. New compounds are in clinical development or under preclinical evaluation, and, again, half of these are targeting HIV infections. Yet, quite a number of important viral pathogens (i.e. HPV, HCV, hemorrhagic fever viruses) remain in need of effective and/or improved antiviral therapies.

Viruses and Viral Diseases

More than 40 compounds have been formally licensed for clinical use as antiviral drugs, and half of these are used for the treatment of human immunodeficiency virus (HIV) infections. The others have been approved for the therapy of herpesvirus (herpes simplex virus (HSV), varicella-zoster virus (VZV), cytomegalovirus (CMV)), hepadnavirus (hepatitis B virus (HBV)), hepacivirus (hepatitis C virus (HCV)), and myxovirus (influenza, respiratory synctural virus (RSV)) infections. New compounds are in clinical development or under preclinical evaluation, and, again, half of these target HIV infections. Yet, quite a number of important viral pathogens (i.e., human papilloma virus (HPV), HCV, hemorrhagic fever viruses) remain in need of effective and/or improved antiviral therapies.