Resistance is starting to appear to Roche’s neuraminidase inhibitor Tamiflu (oseltamivir)
The recent flu scares – first H5N1 bird flu and then H1N1 swine flu – transformed Roche’s neuraminidase inhibitor Tamiflu (oseltamivir) into a household name, along with GSK’s Relenza (zanamivir). Both of these require twice-daily dosing, and the orally available oseltamivir is the first choice, but resistance is starting to appear.
A new neuraminidase inhibitor, laninamivir, is being developed by Daiichi Sankyo.1 When administered as the octanoate prodrug form, it appears that a single dose might be sufficient to treat influenza, weekly doses could be preventative, and it is active against extremely pathogenic H5N1 strains.
In a double blind, randomised, placebo-controlled Phase I study in 76 healthy male volunteers, subjects were given inhaled single doses of 5, 10, 20, 40, 80 or 120mg of the prodrug, or twice-daily doses of 20 or 40mg for three days.2 No adverse events were observed, and while the prodrug disappeared from the plasma with a half-life of about two hours, the laninamivir itself was much more slowly eliminated, with a half-life of the order of three days, suggesting the potential for giving long-lasting activity against influenza.
In another Phase I trial, a total of 20 healthy subjects with renal function ranging from normal to severely impaired were given single inhaled 20mg doses of the prodrug.3 The degree of renal impairment did not affect the maximum concentration or the time to achieve it, but the half-life increased as renal function reduced. This indicates that the rate-limiting step for elimination is drug release rate to plasma from tissues rather than renal excretion. It was well tolerated, but systemic exposure increased with increasing renal impairment.
It has also been compared with oseltamivir in patients with influenza. A total of 186 children under 10 who had had febrile influenza symptoms for no longer than 36 hours were randomised to receive 20 or 40mg of laninamivir octanoate as a single inhalation or 2mg/kg oseltamivir orally twice a day for five days.4
The new drug gave a significant reduction, of 61 hours for the 40mg group and 66 for the 20mg group, in median time to illness alleviation compared with oseltamivir in those with oseltamivir-resistant H1N1 influenza A. However, there was no significant difference in the time to alleviation of illness with H3N2 influenza A, or influenza B.
The most common side-effects were gastrointestinal problems.
In a Phase III trial, a total of 1,003 adult patients with febrile influenza symptoms for no more than 36 hours were given similar doses to those in the trial in children.5 Median time to alleviation of illness was 73h for 40mg, 86h for 20mg, and 74h for oseltamivir, and the proportion of patients shedding virus at day 3 was significantly lower in the 40mg group than for those given oseltamivir.
The company has now submitted the drug for approval.
1. T. Honda et al. Bioorg. Med. Chem. Lett. 2009, 19, 2938
2. H. Ishizuka et al. J. Clin. Pharmacol. 2010, 50, 1319
3. H. Ishizuka et al. J. Clin. Pharmacol. 2010, epub ahead of print, doi 10.1177/0091270010361914
4. N. Sugaya and Y. Ohashi, Antimicrob. Ag. Chemother. 2010, 54, 2575
5. A. Watanabe et al. Clin. Inf. Dis. 2010, 51, 1167