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Flu medications comparisonAt present time four drugs in the United States are approved by the FDA for the treatment and prevention of flu:
In 1976, the U.S. Food and Drug Administration (FDA) approved amantadine to both treat and prevent influenza type A. Rimantadine was approved in 1993 to treat and prevent influenza type A. In 1999, FDA approved two new antiviral medications to fight the flu: zanamivir (Relenza), the first neuraminidase inhibitor, and oseltamivir (Tamiflu), the first of a new class of antiviral drugs called neuraminidase inhibitors. The antiviral drugs approved for influenza in the United States all are prescription drugs. Influenza antiviral medications are drugs that suppress the ability of influenza viruses to reproduce. When used correctly, they can reduce the duration of symptoms and some complications from influenza virus infection. When used for treatment within the first 2 days of illness, all 4 antiviral medications are similarly effective in reducing by 1 or 2 days the duration of illness caused by influenza A viruses, and make you less contagious to others. Only oseltamivir and zanamivir are effective against influenza B viruses. They do not cure influenza outright. All 4 medications are approved for treatment, but oseltamivir and zanamivir are preferred for treatment in part because influenza viruses are more likely to develop resistance to amantadine and rimantadine. The 4 influenza antiviral drugs are effective only against influenza viruses. They will not help reduce symptoms associated with the common cold. All of the antiviral drugs are different in terms of who can take them, approved uses, approved ages, how they are given, any dosing changes based on age or medical conditions, side effects and costs. Zanamivir is inhaled through a device called a Diskhaler. This inhaler device delivers the medicine to the lungs, where the influenza (flu) virus multiplies. Mechanism of Action The surfaces of influenza viruses are dotted with neuraminidase proteins. Neuraminidase inhibitors block the enzyme's activity and prevent new virus particles from being released, thereby limiting the spread of infection. Zanamivir is inhaled through a device called a Diskhaler. This inhaler device delivers the medicine to the lungs, where the influenza (flu) virus multiplies. Oseltamivir is taken as a pill. Zanamivir and oseltamivir help prevent influenza A and influenza B viruses from multiplying in the body by interfering with the production and release of virus from cells that line the respiratory tract. This may slow the spread of the infection within the airways and lungs. Zanamivir and Oseltamivir are selective inhibitors of influenza A and B neuraminidase. Neuraminidase hydrolyzes terminal sialic acid residues from glycoproteins, oligosaccharides, and glycolipids, and is required for infectivity of influenza virus. Neuraminidase is also though to be essential for the release of newly assembled virions from infected cells ---------------- Amantadine and Rimantadine: inhibits entry and uncoating of Influenza
A virus. These drugs block penetration and uncoating of the virus by preventing
acidification of the endosome and thus the pH-dependent activation of
the fusion activity of the virus hemagglutinin by interfering with the
function of the M2 protein of Influenza A virus, which is an ion channel.
Both agents are active against some influenza A virus strains (H1N1, H2N2,
H3N2)7 but are inactive against influenza B (influenza B does not possess
a M2 protein). Medical Uses To treat flu: Symmetrel (amantadine), Flumadine (rimantadine), Tamiflu (oseltamivir), Relenza (zanamivir). To prevent flu: Symmetrel (amantadine), Flumadine (rimantadine), Tamiflu (oseltamivir). Zanamivir is not currently approved for preventive use. Used against influenza type A: Symmetrel (amantadine), Flumadine (rimantadine), Tamiflu (oseltamivir), Relenza (zanamivir). Used against influenza type B: Tamiflu (oseltamivir), Relenza (zanamivir). Dosage forms Amantadine and rimantadine are taken orally in pill form. Tamiflu, the first neuraminidase inhibitor in pill form. It is also available as liquid suspension for children. Zanamivir is administered by inhalation. Zanamivir can be inhaled using a device known as a Diskhaler. Age Zanamivir is used for people age 7 and older. Oseltamivir is used to treat flu in people age 1 or older. Oseltamivir is used to prevent flu in adults and children age 13 and older. Amantadine is used in adults and in children older than age 1. Rimantadine is used to prevent and treat type A influenza in adults. This medication is used prevent influenza A in children over the age of 1 year. Possible Side Effects Side effects differ widely for each antiviral medication. The neuraminidase inhibitors generally cause fewer side effects than the older flu drugs. Amantadine: The most common side effects associated with amantadine relate to the nervous and gastrointestinal systems. Elderly people are especially sensitive to the effects of amantadine. Amantadine may cause light-headedness, difficulty concentrating, dizziness, nervousness, insomnia confusion, loss of balance, and seizures. Elderly patients often have reduced renal function are better treated with Rimantadine, which is 75% metabolized by the liver. Rimantadine: CNS effects like light-headedness, difficulty concentrating, nervousness, insomnia, loss of balance, and seizures side effects occur less often with rimantadine than amantadine. Possible rimantadine side effects include insomnia, dizziness, headache, nervousness, nausea, vomiting. Zanamivir: Some people who have asthma or chronic obstructive pulmonary disease (COPD) and use zanamivir may experience reduced lung function and have difficulty breathing. Other side effects usually do not need medical attention, and may go away as your body adjusts to the medicine. Oseltamivir: The most frequent side effects are nausea, vomiting, diarrhea. These symptoms are mostly mild to moderate and generally occurred within the first two days of administration of the drug. None of these drugs is recommended for use during pregnancy or nursing. These drugs have not been evaluated in pregnant women. Cost Both drugs amantadine and rimantadine are available as generic. Oseltamivir and zanamivir are new medications and are available only as brand name drugs. Therefore, of the four antiviral flu medications, zanamivir and oseltamivir are the most expensive. Conclusions Limiting factors for amantadine are side effects and the need to check renal function especially in elderly patients, as well as the rapid appearance of resistant virus that can be spread to close contacts. The limiting factor for the Neuraminidase inhibitors is cost. The NAIs may be used to treat both A and B influenza and have relatively fewer side effects. Amantadine is the oldest of the anti-influenza drugs, and is seldom used today due to side effects. It is also only effective against influenza A, a less dangerous form of flu than influenza B. The ion channel blockers amantadine and rimantadine are of limited use because of a lack of activity against influenza B virus, side effects, and the rapid emergence of resistant virus strains. Amantadine is, furthermore, associated with several drug interactions. Amantadine usually should not be taken at the same time as antihistamines or other medications that stimulate the central nervous system. These may increase the risk of side effects such as insomnia, anxiety and, at high doses, seizures. Amantadine is removed from the body by the kidneys, rimantadine by the liver. Because side effects occur less often with rimantadine, it may be a better choice. However, rimantadine costs more than amantadine. Adamantane derivatives have significant shortcomings, including narrow therapeutic coverage, treatment-limiting neurological side effects, and the ability to foster development of resistant viruses. Oseltamivir is an antiviral drug that is effective against influenza A and B. It may reduce the duration of flu symptoms by 1 to 2 days or more. It is has recently become famous as an effective treatment for bird flu. In contrast to amantadine and rimantadine, oseltamivir and zanamivir are effective against both influenza A and B in the treatment and post-exposure prophylaxis of influenza. Additionally, due to their mechanism of action, neuraminidase inhibitors are better structured to treat and prevent mutating virus strains. Within the neuraminidase inhibitor class, oseltamivir as an orally administered drug presents advantages over the inhaled administration of zanamivir. The influenza virus A can develop resistance to the antiviral flu medications amantadine and rimantadine. Although influenza viruses A and B have not developed resistance to zanamivir or oseltamivir at this time, resistance is possible with increased use of these medications. |
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