Swine influenza medical therapy

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Medical Therapy

Antiviral Regimen

• Swine influenza

• 1. Condition1: Patients who have severe or progressive clinical illness

• Preferred regimen: Oseltamivir 150 mg PO bid
• Note (1): Treatment duration depends on clinical response
• Note (2): Where the clinical course remains severe or progressive, despite 5 or more days of antiviral treatment, monitoring of virus replication and shedding, and antiviral drug susceptibility testing is desirable
• Note (3): Antiviral treatment should be maintained without a break until virus infection is resolved or there is satisfactory clinical improvement
• Note (4): Patients who have severe or progressive clinical illness, but who are unable to take oral medication may be treated with oseltamivir administered by nasogastric or orogastric tube

• 2. Condition2: In situations where oseltamivir is not available, or not possible to use, patients who have severe or progressive clinical illness

• Preferred regimen: Zanamivir inhaled
• Note: Zanamivir IV should be considered where available and is recommended for those with serious or progressive illness. If not available, Peramivir IV may be considered

• 3. Condition3: Severely immunosuppressed patients

• Preferred regimen: Antiviral chemoprophylaxis by using Oseltamivir OR Zanamivir

The aim is to provide interim guidance on the use of antiviral agents for treatment and chemoprophylaxis of swine influenza A (H1N1) virus infection. This includes patients with confirmed or suspected swine influenza A (H1N1) virus infection and their close contacts.

Suspected Cases

Empiric antiviral treatment is recommended for any ill person suspected to have swine influenza A (H1N1) virus infection. Antiviral treatment witheither zanamivir alone or with a combination of oseltamivir and either amantadine or rimantadine should be initiated as soon as possible after theonset of symptoms. Recommended duration of treatment is five days.Recommendations for use of antivirals may change as data on antiviral susceptibilities become available. Antiviral doses and schedules recommended for treatment of swine influenza A (H1N1) virus infection are the same as those recommended for seasonal influenza:

Confirmed Cases

For antiviral treatment of a confirmed case of swine influenza A (H1N1) virus infection, either oseltamivir or zanamivir may be administered. Recommended duration of treatment is five days.These same antivirals should be considered for treatment of cases that test positive for influenza A but test negative for seasonal influenza viruses H3 and H1 by PCR.

Pregnant Women

Oseltamivir, zanamivir, amantadine, and rimantadine are all “PregnancyCategory C" medications, indicating that no clinical studies have beenconducted to assess the safety of these medications for pregnant women. Onlytwo cases of amantadine use for severe influenza illness during the thirdtrimester have been reported. However, both amantadine and rimantadine havebeen demonstrated in animal studies to be teratogenic and embryotoxic whenadministered at substantially high doses. Because of the unknown effects ofinfluenza antiviral drugs on pregnant women and their fetuses, these four drugsshould be used during pregnancy only if the potential benefit justifies thepotential risk to the embryo or fetus; the manufacturers' package insertsshould be consulted. However, no adverse effects have been reported among womenwho received oseltamivir or zanamivir during pregnancy or among infants born to such women.

Children

Aspirin or aspirin-containing products (e.g. bismuth subsalicylate – Pepto Bismol) should not be administered to any confirmed or suspected ill case of swine influenza A (H1N1) virus infection aged 18 years old and younger due to the risk of Reye syndrome. For relief of fever, other anti-pyretic medications are recommended such as acetaminophen or non steroidal anti-inflammatory drugs.

Antiviral Resistance

This swine influenza A (H1N1) virus is sensitive (susceptible) to the neuraminidaseinhibitor antiviral medications zanamivir and oseltamivir. It is resistant to the adamantane antiviral medications amantadine and rimantadine.

Seasonal influenza A and B viruses continue to circulate at low levels in the U.S. and in Mexico. Currently circulating human influenzaA (H1N1) viruses are resistant to oseltamivir and sensitive (susceptible) to zanamivir, amantadine and rimantadine. Currently circulating human influenza A (H3N2) viruses are resistant to amantadine andrimantadine, but sensitive (susceptible) to oseltamivir and zanamivir. Therefore,at this time antiviral treatment recommendations for suspected cases of swineinfluenza A (H1N1) virus infection need to consider potential infection with swine influenza A (H1N1) virus as wellas human influenza viruses, andtheir different antiviral susceptibilities.