- "A strain [isolate?] of the H5N1 avian influenza
virus that may unleash the next global flu pandemic is showing resistance
- The above statement says it all. Tamiflu is not the panecea
cure-all that we are being led to believe.
- Patricia Doyle
- Experts Warn Of Growing Resistance To Tamiflu
By Tan Ee Lyn
- HONG KONG (Reuters) -- A
strain [isolate?] of the H5N1 avian influenza virus that may unleash the
next global flu pandemic is showing resistance to Tamiflu, the antiviral
drug that countries around the world are now stockpiling to fend off the
looming threat. Experts in Hong Kong said on Friday [30 Sep 2005] that
the human H5N1 strain [isolate?] which surfaced in northern Viet Nam this
year had proved to be resistant to Tamiflu, a powerful antiviral drug.
- They urged drug manufacturers to make more effective
versions of Relenza, another antiviral that is also known to be effective
in battling the much-feared H5N1. Relenza is inhaled [whereas Tamiflu is
taken orally]. "There are now resistant H5N1 strains [isolates] appearing,
and we can't totally rely on one drug (Tamiflu)," William Chui, honorary
associate professor with the Department of Pharmacology at the Queen Mary
Hospital in Hong Kong, told Reuters. Chui was referring to the Tamiflu-resistant
strain of H5N1 [avian influenza] in Viet Nam. Chui also said general viral
resistance to Tamiflu was growing in Japan, where doctors habitually prescribe
the drug to fight common influenza.
- Switzerland's Roche Holdings AG makes Tamiflu, known
generically as oseltamivir, and GalaxoSmithKline makes Relenza, or zanamivir.
"Manufacturers should think about producing an injectable form of
Relenza because resistance to Tamiflu has been seen in Japan and Viet Nam.
Also with injections, high doses can be given where necessary and onset
time is a lot faster," Chui said.
- Drugs that are administered intravenously can be better
absorbed in patients who have stomach and acidity problems, another expert
said. "We don't have to worry about absorption, injections take drugs
right in. But if the patient takes them orally, maybe some amounts won't
be absorbed or some may be destroyed by stomach acids," said pharmacist
Raymond Mak at Queen Mary Hospital. Intravenous Relenza would also ensure
faster onset, which would be critical in patients who are seriously ill.
"Orally taken drugs take 3-4 hours to reach maximum blood concentration
and 3-4 hours is very critical in severe cases. But injectable Relenza
takes only 30 minutes to reach maximum blood concentration, this is a huge
difference," Chui said. With an intravenous antiviral, doctors can
also vary the doses.
- While the H5N1 virus is now mostly passed directly from
bird to human, health experts have warned that it is just a matter of time
before it mutates into a form that is easily transmissible between people.
When that happens, it may result in as many as 150 million human deaths.
- 2 reports in The Lancet this month said that resistance
to anti-influenza drugs was growing worldwide. In places such as China,
drug resistance exceeded 70 percent, suggesting that drugs like amantadine
and rimantadine will probably no longer be effective for treatment or as
a preventive in a pandemic outbreak of flu, the reports said.
- Abstract - The Lancet 2005; 366:1175-1181, Fri 30 Sep
- Cause for Concern: Incidence of Adamantane Resistance
among Influenza A (H3N2) Viruses Isolated Worldwide from 1994 to 2005
- Adamantanes have been used to treat influenza A virus
infections for many years. Studies have shown a low incidence of resistance
to these drugs among circulating influenza viruses; however, their use
is rising worldwide and drug resistance has been reported among influenza
A (H5N1) viruses isolated from poultry and human beings in Asia. We sought
to assess adamantane resistance among influenza A viruses isolated during
the past decade from countries participating in WHO's global influenza
- We analysed data for influenza field isolates that were
obtained worldwide and submitted to the WHO Collaborating Center for Influenza
at the US Centers for Disease Control and Prevention between 1 Oct 1994,
and 31 Mar 2005. We used pyrosequencing, confirmatory sequence analysis,
and phenotypic testing to detect drug resistance among circulating influenza
A H3N2 (n=6524), H1N1 (n=589), and H1N2 (n=83) viruses.
- More than 7000 influenza A field isolates were screened
for specific amino acid substitutions in the M2 gene known to confer drug
resistance. During the decade of surveillance, a significant increase in
drug resistance was noted, from 0.4 percent in 1994-1995 to 12.3 percent
in 2003-2004. This increase in the proportion of resistant viruses was
weighted heavily by those obtained from Asia, with 61 percent of resistant
viruses isolated since 2003 being from people in Asia.
- Our data raise concerns about the appropriate use of
adamantanes and draw attention to the importance of tracking the emergence
and spread of drug-resistant influenza A viruses.
- (Authors: Rick A Bright a, Marie-jo Medina a, Xiyan Xu
a, Gilda Perez-Oronoz a, Teresa R Wallis a, Xiaohong M Davis a, Laura Povinelli
b, Nancy J Cox a, and Alexander I Klimov a: the Division of Viral and Rickettsial
Diseases, National Center for Infectious Diseases, Centers for Disease
Control and Prevention, Influenza Branch, Atlanta, GA, USA b: Wisconsin
State Laboratory of Hygiene, Madison, WI, USA).
- Resistance to amantadine and rimantadine has been recorded
previously, but the high frequency of resistant virus where these drugs
have been used extensively over a considerable period suggests that their
future usefulness will be limited. Resistance to the neuraminidase inhibitors
oseltamivir and zanamivir has generally not been observed. The recent appearance
of a Tamiflu-resistant avian H5N1 influenza virus in Viet Nam is an alarming
development. - Mod.CP
- Patricia A. Doyle, PhD
Please visit my "Emerging
Diseases" message board.
- Zhan le Devlesa tai sastimasa
Go with God and in Good Health