Bird Flu: Tamiflu and Relenza for Prevention and Treatment
According to a recent report on influenza in the Journal of Virology, “Although vaccination is the ideal way to reduce the interspecies spread of influenza viruses, the preparation of a new vaccine takes six months or more. In the interim, antiviral drugs are the only option.” Antiviral drugs can be used for both treatment and prevention of H5N1 bird flu, but have significant limitations. These drugs are expensive, supplies of them are limited, they have to be given within a short time period to be effective, and resistance either has already developed or can develop at any time. Even under optimal circumstances, none of them are 100 percent effective. There are four antivirals that are approved by the U.
Food and Drug Administration (FDA) for use against influenza—two older and inexpensive drugs, amantadine and rimantadine, to which the bird-flu virus has developed significant resistance—and two newer, more expensive and more effective drugs, Roche’s oseltamivir (brand name: Tamiflu), and GlaxoSmithKline’s zanamivir (brand name: Relenza; must be inhaled). The two new drugs belong to a class of antiviral agents called neuraminidase inhibitors. Tamiflu works by blocking the action of a specific enzyme, known as neuraminidase, on the surface of the influenza virus to prevent it from spreading and infecting other cells in the body. Amantadine was once effective against H5N1, but its effectiveness has diminished drastically because the virus has developed resistance against it.
There is some indication, however, that a combination of Tamiflu and amantadine might be more effective than Tamiflu alone. Information about Tamiflu and Relenza is summarized below: Tamiflu (oseltamivir; the first choice for prevention or treatment of bird flu) 1. Prescription antiviral medication approved for treatment of seasonal influenza by the Food and Drug Administration (FDA). Note that use of Tamiflu for treatment or prevention of avian influenza (bird flu) is an “off-label” use of the medication, that is, a use that has not been officially approved by the FDA. However, Tamiflu is widely recognized as the best available medication for prevention or treatment of bird flu, and its use in this situation is recommended by the Centers for Disease Control (CDC) and the World Health Organization (WHO). Mechanism of action: neuraminidase inhibitor (active against all nine influenza A neuraminidase subtypes recognized in nature, including recent pathogenic avian viruses [H5N1, H7N7, N9N2], as well as a virus containing the neuraminidase from the 1918 pandemic strain). Available forms: 75 mg capsules and 12 mg/ml suspension. Effective only if given within 48 hours of onset of symptoms. FDA-approved for treatment for those one year and older. Dose for treatment of influenza for those 12 and older: 75 mg twice daily for five days. Dose for treatment of influenza for those under twelve: 2 mg/kg up to a maximum of 75 mg twice daily for five days. Side effects occurring in five percent or more of patients taking Tamiflu for treatment were nausea, vomiting, and diarrhea. These symptoms generally do not persist with ongoing treatment.
Rare instances of serious side effects have been reported, but they are of uncertain relationship to Tamiflu. FDA-approved for prophylaxis (prevention) of influenza for those 13 and older: a. Dose for prophylaxis of influenza for those 12 and older: 75 mg daily for 10 days. Not approved for prophylaxis of influenza for those younger than 12. However, use of Tamiflu in this situation is probably safe and effective. By deduction, dose should be 1 mg/kg up to a maximum of 75 mg daily for 10 days. Side effects occurring in five percent or more of patients taking Tamiflu for prophylaxis were headache, nausea, and fatigue.
Use in pregnancy: Category C (meaning no scientific studies have been done to prove that it is safe in pregnancy—because of liability, no such studies are ever undertaken—but available evidence indicates that it is probably safe to use during pregnancy). Significant drug interactions: none (although probenecid doubles the level of oseltamivir) How effective is Tamiflu for prevention or treatment of seasonal influenza? Clinical studies have shown the following: Oral oseltamivir is highly protective against experimental human influenza, and early treatment is associated with reductions in viral titers, symptoms, nasal cytokines [inflammatory agents], and middle-ear pressure abnormalities. Early oseltamivir treatment of acute influenza in otherwise healthy adults and children aged one to 12 years reduces the time to illness alleviation by one to 1.5 days, fever duration, and viral titers in the upper respiratory tract. Early treatment reduces time to functional recovery by three days or more. Treatment of children also reduces the risk for otitis media [inner-ear infection] and decreases overall antibiotic use. In healthy and high-risk adults, early treatment decreased the risk for lower respiratory tract complications leading to antibiotics and to hospitalization.
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