Sep 11, 2009.
CHICAGO (Reuters) - Roche Holding AG said on Friday there have been just 23 reported cases in which H1N1 swine flu has resisted the effects of antiviral drug Tamiflu.
Tamiflu, made by Roche and Gilead Sciences Inc, is one of two drugs shown to work well against H1N1 swine flu.
Dr. David Reddy, who leads Roche's pandemic task force, told reporters the number was in line with what the company had observed in its own clinical trials.
"As we see more of the drug used, we will see more of these isolated cases over time," Reddy said in a conference call.
He said there have been no significant clusters of resistance, and no signs that a resistant strain is spreading in any one community.
About 13 of the cases of resistance occurred in people who had been exposed to the new H1N1 virus and were given a low dose of the drug to prevent infection.
In such cases, Reddy said doctors should watch patients closely for signs of illness and consider switching to a stronger, treatment-level dose if a patient actually becomes sick.
Resistance to antiviral drugs has been a concern.
Last year, the seasonal H1N1 flu virus -- a different strain from H1N1 swine flu -- developed resistance against Tamiflu in the United States and many other countries.
Flu viruses are prone to mutation and experts are not surprised that they would evolve resistance, just as bacteria develop resistance to antibiotics.
Tamiflu, known generically as oseltamivir, and GlaxoSmithKline and Biota's Relenza, known generically as zanamivir, not only fight flu. They can prevent infection if given soon enough.
Reddy said Roche has been gearing up its capacity and can now deliver 33 million doses of Tamiflu per month. He said the company is also conducting 13 laboratory studies and 30 studies of the drug.
"Most of our activities are focused around vulnerable populations," including patients with compromised immune systems, severely ill and obese patients, Reddy said.
The company is working with the U.S. Food and Drug Administration on ways to make the drug easier for children to take, including putting it in small capsules, and developing instructions on how to mix Tamiflu with food for children who cannot swallow capsules.
The H1N1 virus has killed at least 3,205 people worldwide since emerging last April in North America and is the predominant flu virus circulating in both hemispheres, according to the World Health Organization's latest weekly update issued separately on Friday.
The U.S. Centers for Disease Control and Prevention said this week that most swine flu patients do not need antivirals, but those who do -- especially those who are having trouble breathing -- should be treated quickly.
H1N1 usually causes mild symptoms, but pregnant women and people with conditions such as asthma are at higher risk.