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But of the two, Tamiflu is by far the more popular. It is the drug that governments are stockpiling to prepare for a full-blown flu pandemic. It is also the drug that many individuals are frantically trying to buy over the internet.
This article looks at the similarities and differences between the two antiviral drugs for flu.
Type of antiviral drugs for flu
In terms of the type of drugs, both Tamiflu and Relenza belong to the same category - Neuraminidase inhibitors. These antiviral drugs work by blocking the function of the neuraminidase protein of the virus, thus preventing the virus from reproducing from inside the cell of its host.
In theory, Neuraminidase inhibitors are effective against both influenza virus Type A and Type B. Influenza Type A is the virus that is more infectious and linked to major flu pandemics, including the current H1N1 flu outbreak.
However, most reports say that only Relenza has proven effective against both types of Influenza viruses whereas Tamiflu is only effective against Type A.
Effectiveness and drug resistance
In terms of effectiveness, earlier reports show that both Tamiflu and Relenza are at least equally effective. For example, a 2005 study published in The Lancet show both drugs to be about equal in terms of effectiveness. A Wikipedia entry reported that in a 2006 study, Tamiflu proved to be less effective than its rival and this led to Germany stockpiling large amounts of Relenza. But no citation was given and the claim could not be verified.
Here, "effective" merely means that the drugs reduce flu symptoms by about one day. Since the average flu patient experiences flu symptoms for seven to 14 days, a reduction of one day is actually no big help. But the medical system is so lacking in solutions that even such a small improvement is being highly sought.
Moreover, in order to be effective, both Tamiflu and Relenza have to be taken in the early stages of the disease - within 48 hours of the onset of a flu, but ideally within six to 12 hours. Since both of these antiviral drugs are available only upon prescription in most countries and many people will not be able to get a prescription so quickly, their effectiveness is limited.
In recent years, drug resistance to Tamiflu has increased dramatically. Two years ago, only about 1 percent of H1N1 flu viruses were found to be resistant to Tamiflu. One year ago, the drug resistance rate rose to about 12 percent. In 2008 / 2009, resistance to Tamiflu has shot up to between 98 and 99 percent of H1N1 flu viruses.
In spite of this, government health authorities keep assuring that Tamiflu is effective against the strain of H1N1 virus associated with the current flu outbreak. Even if this is so, past developments suggest that the effectiveness may not last very much longer.
Meanwhile, there have been no reports of flu viruses being resistant to Relenza. This fact could alter the popularity of this "other flu drug" in the months and years ahead.
Side effects
The side effects of Tamiflu and Relenza are discussed more thoroughly in separate articles.
Generally, Tamiflu is considered to produce more severe side effects. Of particular concern are reports from Japan - where Tamiflu is widely prescribed - about people who developed "bizarre behaviour" and other psychiatric disorders after taking this antiviral drug. These reports include cases of delirium, self-injury and three cases of young people commiting suicide for no apparent reason.
Following these reports, both drugs revised their drug warnings to include "abnormal behavior" as one of the possible side effects.
In the case of Ralenza, a significant side effect is that it might cause bronchospasm - a sudden constriction of the air passage ways, resulting in breathing difficulty and, in some cases death. Patients with a history of asthma and other respiratory diseases are most at risk, but others are not necessarily spared.
Pills vs inhalents
The biggest difference between Tamiflu and Relenza, however, is that the latter has poor oral bioavailability - meaning the drug is not readily available to the body when taken through the mouth. Thus, it is usually inhaled, whereas Tamiflu comes in the form of a pill.
Apart from more aggressive marketing by Roche, the makers of Tamiflu, this is probably the biggest reason why Tamiflu has proven to be the far more popular antiviral drug for flu. GlaxoSmithKline, which makes Relenza, was reported to be considering repackaging the drug as a shot or nebulizer to increase sales.
So far, Tamiflu has succeeded in spite of it costing a lot more. A dose of Tamiflu costs about US$10 to US$12, compared to around US$3 for its rival drug.
But looking at the two antiviral drugs for flu, both are limited in effectiveness and both come with quite serious possible side effects. If you have the flu, you will be much better off with alternative flu treatments, including Traditional Chinese Medicine, Homeopathy, Osteopathy and Chiropractic.
These other systems of healthcare have surprisingly high success rates, epecially during the 1918 Spanish flu.