Tamiflu
Structural studies of the resistance of influenza virus neuramindase to inhibitors.

Smith BJ, McKimm-Breshkin JL, McDonald M, Fernley RT, Varghese JN, Colman PM.

The Walter and Eliza Hall Institute of Medical Research, P.O. Royal Melbourne Hospital, Parkville, Victoria 3050, Australia. bsmith wehi.edu.au

Zanamivir and oseltamivir, specific inhibitors of influenza virus neuraminidase, have significantly different characteristics in resistance studies. In both cases resistance is known to arise through mutations in either the hemagglutinin or neuraminidase surface proteins. A new inhibitor under development by Biocryst Pharmaceuticals, BCX-1812, has both a guanidino group, as in zanamivir, and a bulky hydrophobic group, as in oseltamivir. Using influenza A/NWS/Tern/Australia/G70C/75 (H1N9), neuraminidase variants E119G and R292K have previously been selected by different inhibitors. The sensitivity of these variants to BCX-1812 has now been measured and found in both cases to be intermediate between those of zanamivir and oseltamivir. In addition, the X-ray crystal structures of the complexes of BCX-1812 with the wild type and the two mutant neuraminidases were determined. The ligand is bound in an identical manner in each structure, with a rearrangement of the side chain of E276 from its ligand-free position. A structural explanation of the mechanism of resistance of BCX-1812, relative to zanamivir and oseltamivir in particular, is provided.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12014958&dopt=Abstract oseltamivir Tamiflu



Tamiflu
Utilization of alpha-1-acid glycoprotein levels in the serum as a parameter for in vivo assay of influenza virus inhibitors.

Sidwell RW, Wong MH, Bailey KW, Barnard DL, Jackson MK, Smee DF.

Institute for Antiviral Research, Utah State University, Logan, USA. rsidwell cc.usu.edu

Alpha-1-acid glycoprotein (AGP), an acute phase protein in serum assayed by single radial immunodiffusion using a commercially available kit, was found to significantly increase in mice infected with influenza A and B viruses. Experiments were run to determine the rate of increase of serum AGP and its relation to other influenza disease parameters, including lung consolidation, development of lung virus titres, decline in arterial oxygen saturation (SaO2), histopathological changes in the lung, and death of the animal. Maximal AGP levels occurred by day 3 in the animals, at about the same time lung virus titres reached their peak and inflammatory effects were evident in the lung. Serum levels of AGP were then compared with other disease parameters in the evaluation of the anti-influenza A and B virus efficacy of oseltamivir and ribavirin in mice. Treatment was by oral gavage twice daily for 5 days, beginning 4 h before virus exposure using doses of 100, 10, and 1 mg/kg per day of oseltamivir and 75 mg/kg per day of ribavirin. Against the influenza A infection, significant inhibition of death, SaO2 decline, and lung consolidation was seen at all doses of each compound; day-6 AGP levels were reduced in a dose-responsive manner. Lung virus titres were lessened at this time, but to a significant degree only at the high dose of oseltamivir and by ribavirin. The influenza B virus infection, which appeared more severe than the influenza A infection, was also significantly inhibited by both compounds, but to a lesser extent. The serum AGP levels were again lessened by therapy with both compounds. The influence of challenge dose of influenza A virus on AGP level and on the antiviral activity of 20 mg/kg per day of oseltamivir, administered by oral gavage, was determined in mice. The AGP level was in proportion to the viral challenge dose; oseltamivir significantly inhibited AGP levels and all other disease parameters regardless of size of viral inoculum. These data indicate murine AGP levels to be markedly stimulated by infection with influenza A and B viruses, and the level of the protein to be an additional measure of antiviral efficacy.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12018681&dopt=Abstract oseltamivir Tamiflu



Tamiflu
Experience with oseltamivir in the control of nursing home influenza A outbreak.

Shijubo N, Yamada G, Takahashi M, Tokunoh T, Suzuki T, Abe S.

Third Department of Internal Medicine, Sapporo Medical University School of Medicine.

OBJECTIVE: Influenza outbreaks have revealed that elderly persons are a great risk of death and serious complications after infection. The administration of oseltamivir, a neuramidase inhibitor, is effective for prophylaxis of influenza and to reduce disease duration and severity in healthy adults with naturally acquired febrile influenza. To clarify the usefulness of oseltamivir in the elderly we administered oseltamivir to all residents when an influenza A outbreak occurred in a nursing home. PATIENTS: Sixty-eight residents in the nursing home were investigated in which the influenza A outbreak occurred; 32 residents had fever and 28 residents were positive for influenza A with direct enzyme immunoassay. METHODS: Oseltamivir was administered at 75 mg twice daily for 5 days to all residents. RESULTS: Oseltamivir almost inhibited symptom onset in the influenza A-positive afebrile group. Initiation at 0 hour (22 cases), 1-12 hours (4 cases), 13-24 hours (5 cases) or 72 hours (1 case) from onset of symptoms was associated with mean fever durations of 26+/-18 hours, 38+/-21 hours, 54+/-12 hours and 120 hours, respectively, indicating that earlier initiation of therapy was associated with faster resolution of fever in elderly patients. Oseltamivir may be effective for household prophylaxis in the elderly persons. Oseltamivir administration was well tolerated in elderly persons. CONCLUSION: Oseltamivir is effective for the reduction or prophylaxis of influenza A infection in elderly persons.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12058885&dopt=Abstract oseltamivir Tamiflu



Tamiflu
Susceptibility of recent Canadian influenza A and B virus isolates to different neuraminidase inhibitors.

Boivin G, Goyette N.

Research Center in Infectious Diseases, CHUQ-CHUL, Room RC-709, 2705 Blvd. Laurier, Sainte-Foy, Quebec, Canada G1V4G2. guy.boivin crchul.ulaval.ca

Forty-two influenza A and 23 influenza B isolates collected from untreated subjects during the 1999-2000 influenza season in Canada were tested for their susceptibility to three neuraminidase inhibitors (zanamivir, oseltamivir carboxylate and RWJ-270201 or BCX-1812) using a chemiluminescent neuraminidase assay. Influenza B isolates were less susceptible than A viruses to all tested drugs. RWJ-270201 was the most potent drug against both influenza A(H3N2) (mean IC(50): 0.60 nM) and B (mean IC(50): 0.87 nM) viruses. Oseltamivir carboxylate was more active than zanamivir for influenza A(H3N2) isolates (mean IC(50): 0.73 vs. 2.09 nM) whereas it was less potent against B viruses (mean IC(50): 11.53 vs. 4.15 nM).

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12062387&dopt=Abstract oseltamivir Tamiflu



Tamiflu
Influenza virus carrying neuraminidase with reduced sensitivity to oseltamivir carboxylate has altered properties in vitro and is compromised for infectivity and replicative ability in vivo.

Carr J, Ives J, Kelly L, Lambkin R, Oxford J, Mendel D, Tai L, Roberts N.

Roche Discovery Welwyn, 40 Broadwater Road, Welwyn Garden City, Herts AL7 3AY, UK. jackie.carr roche.com

Oseltamivir phosphate (Tamiflu, Ro 64-0796) is the first orally administered neuraminidase (NA) inhibitor approved for use in treatment and prevention of influenza virus infection in man. Oseltamivir phosphate is the pro-drug of the active metabolite oseltamivir carboxylate (Ro 64-0802). Extensive monitoring throughout the oseltamivir development programme has identified a very low incidence of patients who have carried drug-resistant virus. The predominant mutation seen is the substitution of arginine for lysine at position 292 of the viral NA. The fitness of clinically isolated influenza virus A/Sydney/5/97 (H3N2) carrying this mutation was markedly reduced in animal models of influenza virus infection. The infectivity and replicative abilities of R292K mutant virus were reduced by at least 2 logs in a mouse model of influenza infection and by 2 and 4 logs, respectively, in the ferret model. Pathogenicity of R292K influenza virus A/Sydney/5/97 was reduced in ferrets as measured by inflammatory and febrile responses at least in parallel to the decrease in replicative ability. The data indicate that the R292K NA mutation compromises viral fitness such that virus carrying this mutation is unlikely to be of significant clinical consequence in man.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12062393&dopt=Abstract oseltamivir Tamiflu