Yesterday the article below appeared and caused mass confusion and panic.

In this article, I attempt to clear some misconceptions as noted from the article.

By MIKE STOBBE, AP Medical Writer Mike Stobbe, Ap Medical Writer– Fri Nov 20, 5:18 pm ET

Tamiflu-resistant swine flu cluster reported in NC

ATLANTA – Four North Carolinapatients at a single hospital tested positive for a type of swine flu that is resistant to Tamiflu, health officials said Friday.

What I want cleared up is this,drug-resistant viruses were not ‘reactions’ to overuse of the drug. The drug selects, from the diverse viral population in an individual, those viruses that can multiply in its presence. Usually the drug-resistant mutants are already in the host, and outpace other drug-sensitive viruses. What apparently happened is that the mutation that causes drug-resistance, a change from histidine to tyrosine at position 274 of the viral NA protein, emerged.  This change did not affect resistance to Tamiflu, but apparently it only persisted when the change at 274 was also present. It so happened that the 274 change also conferred resistance to Tamiflu. Thus, when this virus arrived in parts of the world where Tamiflu is used, the resistance was noted. None of this is made particularly clear from the article.

What about the two other anti-influenza drugs? And the other strain currently circulating, H3N2?

Most of the flu in the US now is caused by H1N1 strains. So although the H3N2 strains are sensitive to Tamiflu, it’s not much help.

The Tamiflu-resistant H1N1 strains are sensitive to another drug, Relenza (zanamivir). But that drug must be inhaled and is not appropriate for everyone. However, these H1N1 strains are sensitive to Rimantadine, so its use is a good alternative. Most H3N2 strains are resistant to Rimantadine, which is why it has not been used much in recent years.

What is key and must be remebered is that Tamiflu and Relenza  remain effective in 99% of the cases when used

TAMIFLU-Oseltamivir is an oral medication used for treating and preventing the "flu." Oseltamivir suppresses and decreases the spread of influenza A and B viruses, the viruses responsible for the flu. It does this by blocking the action of neuraminidase, an enzyme produced by the viruses that enables the viruses to spread from infected cells to healthy cells. By preventing the spread of virus from cell to cell, the symptoms and duration of influenza infection are reduced. On average, oseltamivir reduces the duration of symptoms by one and a half days if treatment is started within forty-eight hours of the beginning of symptoms. The FDA approved oseltamivir in October 1999.

Relenza -Zanamivir is an inhaled medication used for treating and preventing influenza or the "flu." Zanamivir suppresses and decreases the spread of influenza A and B viruses, the viruses responsible for the flu. It does this by blocking the action of neuraminidase, an enzyme produced by the viruses that enables the viruses to spread from infected cells to healthy cells. By preventing the spread of virus from cell to cell, the symptoms and duration of influenza infection are reduced. On average, zanamivir reduces the duration of symptoms by one day if treatment is started within forty-eight hours after symptoms begin. The FDA approved zanamivir in July 1999.

Contributions from the CDC, Virology Dept .