H1N1 Influenza (Swine Flu) Medication
- Author: Michael Stuart Bronze, MD; Chief Editor: Russell W Steele, MD more...
Laboratory testing has found the H1N1 influenza A (swine flu) virus susceptible to the prescription antiviral drugs oseltamivir and zanamivir. Other antiviral agents (eg, amantadine, rimantadine) are not recommended because of recent resistance to other influenza strains documented over the past several years.
The usual vaccine for influenza administered at the beginning of the flu season is not effective for this viral strain. Also, other antiviral agents (eg, amantadine, rimantadine) are not recommended because of recent resistance to other influenza strains documented over the past several years.
Basic supportive care (ie, hydration, analgesics, cough suppressants) should be prescribed. Empiric antiviral treatment should be considered for confirmed, probable, or suspected cases of H1N1 influenza. Treatment of hospitalized patients and patients at higher risk for influenza complications should be prioritized.
WHO guidelines recommend treating serious cases immediately. The guidelines represent an international panel of experts who reviewed all available studies regarding antiviral agents (with emphasis on oseltamivir and zanamivir). Evidence indicates that oseltamivir, when properly prescribed, significantly decreases risk of pneumonia (a leading cause of death for both pandemic and seasonal influenza) and the need for hospitalization.
In the 2009 H1N1 pandemic, oseltamivir-resistant strains were observed in a small number of patients. Most oseltamivir resistance occurred in severely immunocompromised patients with prior exposure to oseltamivir.
For patients who initially present with severe illness or whose condition begins to deteriorate, initiate oseltamivir as soon as possible. For patients with severe or deteriorating illness, treatment should be provided even if started later. Where oseltamivir is unavailable or cannot be used for any reason, zanamivir may be given. This recommendation applies to all patient groups, including pregnant women, and all age groups, including young children and infants.
For patients with underlying medical conditions that increase the risk of more severe disease, WHO recommends treatment with either oseltamivir or zanamivir. These patients should also receive treatment as soon as possible after symptom onset, without waiting for the results of laboratory tests. Pregnant women are included among groups at increased risk, and WHO recommends that pregnant women receive antiviral treatment as soon as possible after symptom onset.
At the same time, the presence of underlying medical conditions will not reliably predict all or even most cases of severe illness. Worldwide, around 40% of severe cases are now occurring in previously healthy children and adults, usually younger than 50 years. Some of these patients experience a sudden and very rapid deterioration in their clinical condition, usually on day 5 or 6 following the onset of symptoms.
Clinical deterioration is characterized by primary viral pneumonia, which destroys the lung tissue and does not respond to antibiotics, and the failure of multiple organs, including the heart, kidneys, and liver. These patients require management in intensive care units using therapies in addition to antivirals.
Peramivir, an investigational, intravenous neuraminidase inhibitor in Phase 3 clinical trials, has been used successfully in adults and children under an emergency investigational new drug program in the United States. It was well tolerated and associated with recovery in the majority of patients hospitalized with severe H1N1 infection.
Initiate antiviral agents within 48 hours
Prompt initiation of antiviral agents within 48 hours of symptom onset is imperative for providing treatment efficacy against influenza virus. In studies of seasonal influenza, evidence for benefits of treatment is strongest when treatment is started within 48 hours of illness onset. However, some studies of treatment of seasonal influenza have indicated benefit, including reductions in mortality or duration of hospitalization, even in patients in whom treatment was started more than 48 hours after illness onset. The recommended duration of treatment is 5 days.[30, 31]
Prophylaxis with antiviral agents should also be considered in the following individuals (pre-exposure or postexposure):
Close household contacts of a confirmed or suspected case who are at high risk for complications (eg, chronic medical conditions, persons >65 y or < 5 y, pregnant women)
School children at high risk for complications who have been in close contact with a confirmed or suspected case
Travelers to Mexico who are at high risk for complications (eg, chronic medical conditions, persons >65 y or < 5 y, pregnant women)
Health care providers or public health workers who were not using appropriate personal protective equipment during close contact with a confirmed or suspected case
In September 2009, the CDC updated recommendations concerning the use of antiviral medications for prevention because of reported oseltamivir resistance; antivirals should not be used for postexposure chemoprophylaxis in healthy children or adults to manage outbreaks in the community, school, camp, or other settings. 
Reserve antiviral chemoprophylaxis for persons at higher risk for influenza-related complications who have had contact with someone likely to have been infected with influenza.
Pre-exposure prophylaxis can be considered in the following persons:
Any health care provider who is at high risk for complications (eg, persons with chronic medical conditions, adults >65 y, pregnant women)
Individuals not considered to be at high risk but who are nonetheless traveling to Mexico, first responders, or border workers who are working in areas with confirmed cases
Oseltamivir ring prophylaxis can be considered for outbreaks of pandemic H1N1 influenza A, especially among closed populations such as military personnel; ring prophylaxis involved the use of oseltamivir 75 mg once daily to members of the same military unit where contact opportunities were substantial. 
Aspirin or aspirin-containing products (eg, bismuth subsalicylate [Pepto Bismol]) should not be included in the treatment of confirmed or suspected viral infection in persons aged 18 years or younger because of the risk of Reye syndrome. For relief of fever, other antipyretic medications (eg, acetaminophen, nonsteroidal anti-inflammatory drugs) are recommended.
Oseltamivir and zanamivir are "Pregnancy Category C" medications, indicating that no clinical studies have been conducted to assess the safety of these medications in pregnant women.
Because of the unknown effects of influenza antiviral drugs on pregnant women and their fetuses, oseltamivir or zanamivir should be used during pregnancy only if the potential benefit justifies the potential risk to the embryo or fetus; the manufacturers' package inserts should be consulted. However, no adverse effects have been reported among women who received oseltamivir or zanamivir during pregnancy or among infants born to women who have received oseltamivir or zanamivir.
Prompt use of antiviral drugs during the 2009 H1N1 influenza pandemic improved survival among severely ill pregnant women. The CDC examined reports of severe flu (resulting in death or ICU admission) in 347 pregnant women during the pandemic, including 272 who were admitted to the ICU and survived and 75 who died. Severely ill postpartum women (n=15), including 9 who died, also were reported.
Of the 307 pregnant women for whom information regarding the presence of underlying medical conditions was available, half had underlying conditions such as asthma, diabetes, or hypertension. Among those who died, 86.1% received antiviral treatment with oseltamivir or zanamivir, compared with 94.8% of survivors. Time to initiate treatment from symptom onset was significantly different for women who died, compared with those who survived (P < .01). Only 4 women (7%) of those who died received an antiviral within 2 days of symptom onset, compared with 41% of survivors.
This analysis reaffirms the importance of prevention (ie, vaccination of pregnant women regardless of trimester) and prompt treatment with a neuraminidase inhibitor (ie, within 2 d of symptom onset) if influenza occurs during pregnancy.
Pregnancy should not be considered a contraindication to oseltamivir or zanamivir use. Because zanamivir is an inhaled medication and has less systemic absorption, some experts prefer zanamivir over oseltamivir for use in pregnant women, when feasible.[30, 35] Others recommend that, because pregnant women may have a decreased ability to inhale zanamivir, they should be given oseltamivir.
Drugs indicated for treatment of H1N1 influenza A virus include neuraminidase inhibitors (ie, oseltamivir and zanamivir).
Oseltamivir and zanamivir inhibit neuraminidase, which is a glycoprotein on the surface of influenza virus that destroys an infected cell's receptor for viral hemagglutinin. By inhibiting viral neuraminidase, these agents decrease the release of viruses from infected cells and, thus, viral spread.
These antivirals are effective in the treatment of influenza A or B and must be administered within 48 hours of symptom onset to provide optimal treatment. The sooner the drug is administered after symptom onset, the better the likelihood of a good outcome. However, some studies of treatment of seasonal influenza have indicated benefit, including reductions in mortality or duration of hospitalization even for patients whose treatment was started more than 48 hours after illness onset. Antivirals reduce the length of illness by an average of 1.5 days. (In a subgroup of high-risk patients, illness was reduced by 2.5 d.) In addition, the severity of symptoms is also reduced.
On October 23, 2009, the FDA announced emergency-use authorization of the investigational intravenous neuraminidase inhibitor, peramivir. In an observational study of 31 patients, intravenous peramivir was administered to patients with progressive H1N1 pneumonia despite treatment with oseltamivir. Peramivir was well-tolerated, and the 56-day survival rate was 59%. Further studies are necessary to evaluate the effectiveness of peramivir. To request peramivir, see the information at the CDC's H1N1 website or call (800) CDC-INFO (232-4636).
Inhibits neuraminidase, which is a glycoprotein on the surface of influenza virus that destroys an infected cell's receptor for viral hemagglutinin. By inhibiting viral neuraminidase, decreases release of viruses from infected cells and thus viral spread. Effective to treat influenza A or B. Start within 40 h of symptom onset. Available as 30-mg, 45-mg, and 75-mg oral capsules and as a powder for suspension that contains 12 mg/mL after reconstitution.
Inhibitor of neuraminidase, which is a glycoprotein on the surface of the influenza virus that destroys the infected cell's receptor for viral hemagglutinin. By inhibiting viral neuraminidase, release of viruses from infected cells and viral spread are decreased. Effective against both influenza A and B. Inhaled through Diskhaler oral inhalation device. Circular foil discs containing 5-mg blisters of drug are inserted into supplied inhalation device.
Individuals with asthma or other respiratory conditions that may decrease ability to inhale the drug should be given oseltamivir (eg, asthma, pregnancy). Severe respiratory failure caused by H1N1 influenza has been reported in the southern hemisphere during July and August 2009; therefore, in severely ill patients, the ability to inhale zanamivir may be impaired.
Investigational neuraminidase inhibitor. Emergency-use authorization issued by US FDA for use of peramivir in hospitalized adult and pediatric patients with suspected or laboratory-confirmed 2009 H1N1 influenza unresponsive to oseltamivir or zanamivir, unable to take PO or inhaled drugs (or delivery route not dependable or feasible), or other circumstances determined by clinician. To request peramivir, see information at www.cdc.gov/h1n1flu/eua or call (800) CDC-INFO (232-4636).
A systematic review and meta-analysis has reported on the immunogenicity and safety of the 2009 influenza A (H1N1) vaccine. No death or case report of Guillain-Barre was reported and the vaccine, with or without adjuvant, appeared to be generally seroprotective after one dose among those aged older than 36 months.
Each year in the United States, a vaccine that contains antigens from the strains most likely to cause infection during the winter flu season is produced. For the trivalent formulation influenza vaccines, 2 strains of influenza A and 1 of influenza B are included. The quadrivalent vaccines contain an additional influenza B strain. The trivalent 2013-2014 northern hemisphere vaccine contains the following components:
- A/California/7/2009 (H1N1)-like (same strain as was used for 2009 H1N1 monovalent vaccines)
- A/Texas/50/2012 (H3N2), replaces A/Victoria/361/2011
- B/Massachusetts/2/2012-like (B/Yamagata lineage), replaces B/Wisconsin/1/2010-like
The quadrivalent influenza vaccines contain the following additional B strain in addition to the 3 viral strains listed above:
- B/Brisbane/60/2008-like (B/Victoria lineage)
The vaccine is available in a variety of dosage forms. The IM injection contains 45 mcg of hemagglutinin of influenza per 0.5 mL and uses a 1- to 1.5-inch needle. A microinjection system for intradermal delivery (Fluzone Intradermal) features an ultrafine needle that is 90% shorter than the typical needle used for IM injections. The intradermal dosage form contains 27 mcg/0.1 mL of influenza hemagglutinin. In both younger and older adults, the AS03 adjuvant system improves immune response to inactivated 2009 H1N1 influenza vaccine. The AS03 adjuvant system is well tolerated.
Influenza vaccine is also available as a quadrivalent nasal spray (FluMist Quadrivalent) for healthy children 2 years or older, adolescents, and adults younger than 50 years. Clinical trials are limited in scope regarding the protective effects of live vaccine. The live virus is attenuated by cold; therefore, only very limited viral replication occurs at temperatures of more than 95°F.
A recombinant trivalent vaccine (Flublok) is also available for adults aged 18-49 years. It is made from hemagglutinin proteins that are not derived from egg or chick embryo.
Influenza virus vaccine trivalent (Afluria, FluLaval, Fluarix, Flucelvax, Fluvirin, Fluzone, Fluzone High-Dose, Fluzone Intradermal)
Influenza vaccine is indicated for active immunization to prevent infection from influenza A and B viruses. The vaccine induces antibodies specific to virus strains contained in the vaccine. The US Public Health Service determines influenza vaccine contents annually. Typically, 3 live attenuated virus strains, which antigenically represent the influenza strains likely to circulate the next flu season, are included in the formulation each year. Fluzone is approved for children as young as 6 months, Fluarix for children aged 3 years or older, Fluvirin for children aged 4 years or older, and Afluria for children aged 5 years or older.
This vaccine is made from recombinant hemagglutinin proteins that are not derived from egg or chick embryo. Influenza vaccine is indicated for active immunization to prevent infection from influenza A and B viruses. The vaccine induces antibodies specific to virus strains contained in the vaccine. The US Public Health Service determines influenza vaccine contents annually. Typically, 3 live attenuated virus strains, which antigenically represent the influenza strains likely to circulate the next flu season, are included in the formulation each year. It is administered as an IM injection and approved for adults aged 18-49 years.
Quadrivalent vaccines contain 2 strains of influenza A and 2 strains of influenza B. The vaccine induces antibodies specific to virus strains contained in the vaccine. Each year, the US Public Health Service determines which viral strains will be included in the seasonal influenza vaccine that will antigenically represent the viral strains most likely to circulate in the next flu season. It is administered as an IM injection and approved for adults and children 3 years or older.
The intranasal influenza vaccine is indicated for active immunization to prevent influenza A and B viruses in healthy children, adolescents, and adults. Quadrivalent vaccines contain 2 strains of influenza A and 2 strains of influenza B. The vaccine induces antibodies specific to virus strains contained in the vaccine. Each year, the US Public Health Service determines which viral strains will be included in the seasonal influenza vaccine that will antigenically represent the viral strains most likely to circulate in the next flu season.
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