Oseltamivir acid is an active metabolite of Oseltamivir, which is a potent and selective inhibitor of influenza A and B virus neuraminidases.

Influenza A and B^[1]

Oseltamivir acid inhibits virus replication in vitro and in vivo. Influenza B and A/H1N1 viruses appeare to be sensitive to Oseltamivir (mean B IC₅₀ value: 13 nM; mean H1N1 IC₅₀ value: 1.34 nM), while A/H1N2 and A/H3N2 viruses are more sensitive to Oseltamivir (mean H3N2 IC₅₀ value: 0.67 nM; mean H1N2 IC₅₀ value: 0.9 nM)^[1]. In neuraminidases inhibition assays with influenza A viruses, the median 50% inhibitory concentration (IC₅₀) of RWJ-270201 (approximately 0.34 nM) is comparable to that of Oseltamivir carboxylate (0.45 nM) For influenza B virus isolates, the IC₅₀ of RWJ-270201 (1.36 nM) is comparable to that of Zanamivir (2.7 nM) and less than that of Oseltamivir carboxylate (8.5 nM)^[2].

Oseltamivir (0.1, 1, or 10 mg/kg/day, twice daily by oral gavage) produces a dose-dependent antiviral effect against Vietnam/1203/04 (VN1203/04) virus. The 5-day regimen at 10 mg/kg/day protects 50% of mice; deaths in this treatment group are delayed and indicated the replication of residual virus after the completion of treatment. Eight-day regimens improved Oseltamivir efficacy, and dosages of 1 and 10 mg/kg/day significantly reduced virus titers in organs and provided 60% and 80% survival rates, respectively^[3]. In the pharmacokinetic study, after the oral administration of 1,000 mg/kg Oseltamivir, peak plasma concentrations are reached at 2 h postdose for Oseltamivir and 8 h for Oseltamivir carboxylate (OC). Rats are exposed to Oseltamivir over the whole sampling interval and had a ~2.7-fold-higher rate of exposure to OC than Oseltamivir. In CSF, peak concentrations are reached at 2 h postdose for Oseltamivir and 6 h for OC. CSF/plasma exposure ratios (AUC_{0-8 h}) are ~0.07 for Oseltamivir and 0.007 for OC. In perfused brain samples, peak concentrations are reached at 8 h postdose for Oseltamivir and 6 h for OC. Brain/plasma exposure ratios (AUC_{0-8 h}) of ~0.12 for Oseltamivir and 0.01 for OC are recorded. Corresponding CSF/brain exposure ratios ranged between ~0.55 and 0.64 for both analytes. A further group of animals that received a single oral administration of Oseltamivir at a lower dose produced similar results^[4].

• [1]. Ferraris O, et al. Sensitivity of influenza viruses to zanamivir and oseltamivir: a study performed on viruses circulating in France prior to the introduction of neuraminidase inhibitors in clinical practice. Antiviral Res. 2005 Oct;68(1):43-8.

  [2]. Gubareva LV, et al. Comparison of the activities of zanamivir, oseltamivir, and RWJ-270201 against clinical isolates of influenza virus and neuraminidase inhibitor-resistant variants.Antimicrob Agents Chemother. 2001 Dec;45(12):3403-8.

  [3]. Yen HL, et al. Virulence may determine the necessary duration and dosage of oseltamivir treatment for highly pathogenic A/Vietnam/1203/04 influenza virus in mice. J Infect Dis. 2005 Aug 15;192(4):665-72.

  [4]. Hoffmann G, et al. Nonclinical pharmacokinetics of oseltamivir and oseltamivir carboxylate in the central nervous system. Antimicrob Agents Chemother. 2009 Nov;53(11):4753-61.

Oseltamivir is dissolved in sterile PBS (Mice)^[3].

Mice^[3]
Female 6-week-old BALB/c mice are anesthetized with isofluorane and intranasally inoculated with 50 μL of 10-fold serial dilutions of VN1203/04 virus in PBS. The mouse lethal dose (MLD₅₀) is calculated after a 16-day observation period. Oseltamivir is administered by oral gavage twice daily for 5 or 8 days to groups of 10 mice at dosages of 0.1, 1, and 10 mg/kg/day. Control (infected but untreated) mice received sterile PBS (placebo) on the same schedule. Four hours after the first dose of Oseltamivir, the mice are inoculated intranasally with 5 MLD₅₀ of VN1203/04 virus in 50 μL of PBS. Survival and weight change are observed for 24 days. Virus titers in the mouse organs are determined on days 3, 6, and 9 after inoculation. Three mice from each experimental and placebo group are killed, and the lungs and brains are removed. The organs are homogenized and suspended in 1 mL of PBS. The cellular debris is cleared by centrifugation at 2000 g for 5 min. The limit of virus detection is 0.75 log₁₀ EID₅₀. For calculation of the mean, samples with a virus titer <0.75>₁₀ EID₅₀/mL are assigned a value of 0. Virus titers in each organ are calculated by use of the method of Reed and Muench and are expressed as mean log₁₀ EID₅₀/mL±SE.
Rat^[4]
Several studies are performed to characterize the pharmacokinetics of Oseltamivir and OC in the plasma, cerebrospinal fluid (CSF), and brain of Sprague-Dawley rats following single-dose bolus administration of Oseltamivir (intravenous [i.v.] and oral) and OC (i.v.). In the i.v. studies, nonfasted adult rats (two groups of 35 animals for each test substance) received a dose of 30 mg/kg body weight of either Oseltamivir or Oseltamivir carboxylate (OC) in aqueous solution with sodium chloride (0.9%; pH 4.0) via slow injection into the tail vein over 20 to 30 s. In both i.v. studies, pharmacokinetic sampling took place at 5 min and at 0.25, 0.5, 1, 2, 4, and 8 h postdose (four or five rats/time point). MCE has not independently confirmed the accuracy of these methods. They are for reference only.

• [1]. Ferraris O, et al. Sensitivity of influenza viruses to zanamivir and oseltamivir: a study performed on viruses circulating in France prior to the introduction of neuraminidase inhibitors in clinical practice. Antiviral Res. 2005 Oct;68(1):43-8.

  [2]. Gubareva LV, et al. Comparison of the activities of zanamivir, oseltamivir, and RWJ-270201 against clinical isolates of influenza virus and neuraminidase inhibitor-resistant variants.Antimicrob Agents Chemother. 2001 Dec;45(12):3403-8.

  [3]. Yen HL, et al. Virulence may determine the necessary duration and dosage of oseltamivir treatment for highly pathogenic A/Vietnam/1203/04 influenza virus in mice. J Infect Dis. 2005 Aug 15;192(4):665-72.

  [4]. Hoffmann G, et al. Nonclinical pharmacokinetics of oseltamivir and oseltamivir carboxylate in the central nervous system. Antimicrob Agents Chemother. 2009 Nov;53(11):4753-61.

284.35

C₁₄H₂₄N₂O₄

187227-45-8

Room temperature in continental US; may vary elsewhere

H₂O: ≥ 56 mg/mL

* "<1 mg/ml"="" means="" slightly="" soluble="" or="" insoluble.="" "≥"="" means="" soluble,="" but="" saturation="">