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Comparing Antivirals and Understanding Safety Precautions and Resistance

Precautions to Take With Antiviral Medications

People who are allergic to antiviral drugs or their ingredients should not take them.
Relenza is not generally recommended for people with chronic respiratory diseases such as asthma or chronic obstructive pulmonary disease (COPD). In clinical studies, some patients with mild or moderate asthma or COPD had bronchospasm (wheezing) after taking Relenza. If you have an underlying respiratory disease and have been prescribed Relenza, your healthcare provider should instruct you to have a fast-acting inhaled bronchodilator available for use when taking the drug.
The dosage of Tamiflu may need to be adjusted if you have any type of kidney disease.
None of these antiviral drugs are recommended for routine use during pregnancy or nursing. These drugs have not been evaluated in pregnant women, and researchers do not know the effects these drugs could have on the unborn child.
In laboratory and in limited clinical studies, there have been no reported interactions of the neuraminidase inhibitors with other drugs. You should talk with your pharmacist or healthcare provider about precautions you should take prior to taking antiviral drugs.


When either Symmetrel or Flumadine is used as a flu treatment, drug-resistant flu viruses may appear in about one-third of patients. Laboratory studies have shown that influenza A and B viruses can develop resistance to Relenza and Tamiflu. Currently, there are studies being done on neuraminidase inhibitor-resistance.

How Do Antiviral Drugs Compare to Each Other?

There have not been any studies to date that have directly compared the effectiveness of Relenza, Tamiflu, Symmetrel, and Flumadine for treating influenza A, or Relenza and Tamiflu for treating influenza A or B. The available information suggests that these antiviral drugs are similarly effective in reducing the duration of uncomplicated acute illness due to influenza A.
Relenza and Tamiflu differ from Symmetrel and Flumadine in terms of their side effects and cost. Symmetrel (and to a lesser extent Flumadine) has been associated with central nervous system side effects, including nervousness, anxiety, insomnia, and lightheadedness. These side effects have not been associated with Relenza or Tamiflu.
On the other hand, Relenza and Tamiflu are significantly more expensive than either Flumadine or Symmetrel.
All four antiviral drugs are available by prescription only. Therefore, you should consult with your healthcare provider to determine what drug might be best for you.
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