December 22, 2005

Signs of Tamiflu resistance no cause for alarm -WHO

By Stephanie Nebehay

GENEVA (Reuters) - Signs that the H5N1 bird flu virus may be developing resistance to the frontline drug Tamiflu in some patients are not necessarily a cause for alarm, a senior World Health Organization official said on Thursday.

Keiji Fukuda, an expert at the WHO's global influenza program, said some resistance was inevitable with any kind of drug, and Tamiflu still remained the best treatment option.

"Whenever you use any kind of drugs, antivirals or antibiotics, you expect to see resistance develop in organs. Finding some resistance in and of itself is not surprising and is not necessarily alarming," Fukuda told Reuters.

But more research was needed on optimal doses and length of treatment for people infected with the deadly virus, to limit the chances of resistance becoming more widespread, he added.

Findings published in the New England Journal of Medicine showed that four of eight patients treated in Vietnam for bird flu infections had died despite the use of Tamiflu.

"It just points out the need for more information ... What really is critical is understanding whether the way we are using the drugs contributes to that (resistance)," Fukuda said.

According to the study, tests showed that in two of the patients, the virus had developed resistance to Tamiflu, which is made by Swiss drugs firm Roche. For the other two, treatment may simply have started too late.

Roche shares were down 0.8 percent at 6:30 a.m. EST.


Using doses that are too small, or for too short a time, can contribute to resistance developing, according to Fukuda, who noted that the Vietnam study had been very small.

"We have to monitor the situation to see whether resistance becomes a big problem or not," Fukuda said.

Tamiflu remained an "excellent choice" among a limited number of antivirals available, he said.

GlaxoSmithKline and Biota's Relenza, known generically as zanamivir, is an alternative to Tamiflu and has been shown to be active against Tamiflu-resistant virus.

But Relenza must be inhaled, making it problematic for patients with respiratory conditions such as asthma.

Glaxo hopes eventually to develop an injectable form of the medicine to overcome this limitation, but a spokeswoman in London said it was unlikely to be ready for at least two years.

Two more human deaths from bird flu in Indonesia were confirmed on Thursday, taking the known global total to 73. All the deaths so far have been in Asia.

Experts fear the virus will mutate into one that can be passed from human to human, rather than from bird to people, and that such a mutation might spark a pandemic killing millions.

"Given the current situation and the need to be as prepared as possible for the pandemic, antivirals remain a really important part of our preparations. This paper does not call into question whether we should be doing that," Fukuda said.

Options for antivirals, in terms of both stockpiling and treatment of patients infected with the virus, remain "relatively limited," according to Fukuda.

On balance, a class of drugs known as neuraminidase inhibitors is the best bet, with Tamiflu an "excellent choice" among them, he added.

(With additional reporting by Ben Hirschler in London)