Less than 50% of the U.S. population obtains the seasonal influenza vaccine, and the vaccine does not confer perfect immunity. There are three types of influenza, plus numerous variations. Practitioners should be confident in the use of antiviral agents in patients with influenza. The most recent guidelines recommend the use of nonpharmacologic management and neuraminidase inhibitors to either prevent the transmission of influenza or treat the infection. Pharmacotherapy is based on an understanding of which
Nonpharmacologic Treatment: Nonpharmacologic recommendations for influenza are bed rest, avoidance of other persons, and hydration. Fluids should be consumed throughout the illness to prevent complications from dehydration. Acetaminophen or ibuprofen may be used to relieve fever, headache, and muscle aches. However, some patients may benefit from antiviral treatment (see Pharmacotherapy Considerations section).17-19
Pharmacologic Agents: Antiviral medications with activity against influenza viruses are an important adjunct to vaccination for control of the influenza virus. Oseltamivir (Tamiflu), inhaled zanamivir (Relenza), and IV peramivir (Rapivab) are the currently recommended agents for influenza.20-22 These drugs, which are neuraminidase inhibitors with activity against both influenza A and influenza B, work by selectively inhibiting the neuraminidase enzyme, thereby preventing the release of viral particles from infected cells. These medications may be used for treatment, but only oseltamivir and zanamivir may be used for treatment and chemoprophylaxis. The chemoprophylaxis dosages for these drugs are lower than the treatment dosages; however, the therapy duration is longer (TABLE 1).20-23 Oseltamivir and zanamivir are indicated for use in adults and children; peramivir has not been FDA-approved for use in children.19,23
Besides the neuraminidase inhibitors, two other products are available: amantadine (Symmetrel) and rimantadine (Flumadine), both of which are adamantane antiviral agents with activity against influenza A viruses. These agents exert an inhibitory effect on influenza A subtypes (H1N1, H2N2, and H3N2) early in the viral replicative cycle. However, they are no longer recommended for treatment and prevention of influenza because of the increased rates of resistance (>99%) in influenza A types H3N2 and H1N1.19,23
Early treatment with the previously mentioned antivirals can shorten the duration of influenza symptoms by 1/2 day to 3 days and may reduce the risk of complications.24 The greatest clinical benefit is seen when antiviral treatment is initiated within 48 hours of illness onset. It is also important to correctly identify patients who meet parameters for either chemoprophylaxis or treatment so that they receive the correct dosage and duration of therapy.19
Chemoprophylaxis should be considered in adults and children aged 1 year and older who are at high risk for developing influenza complications and for whom influenza vaccination is contraindicated, unavailable, or expected to have low effectiveness (e.g., significantly immunocompromised persons).18,19 Chemoprophylaxis should also be considered in this population when the vaccination has not yet been administered and influenza has been detected within the community. Unvaccinated adults—including healthcare workers—and children aged ≥1 year who are in close contact with persons at high risk for developing influenza complications during periods of influenza activity should be considered for chemoprophylaxis, as should all vaccinated and unvaccinated persons in institutions experiencing influenza outbreaks.19
Antiviral treatment should be initiated in all persons with laboratory-confirmed or highly suspected influenza virus infection, including those at high risk for developing complications (TABLE 2).19 Patients who require hospitalization for influenza regardless of vaccination status or underlying illness should also receive treatment. Outpatients at high risk for complications whose illness is not improving and who have a positive influenza test result may be candidates for influenza treatment. The same is true for outpatients who are not at increased risk, but wish to shorten the duration of illness or are in close contact with someone at high risk for complications secondary to influenza infection.19
When the appropriate drug for chemoprophylaxis or treatment is being selected, local patterns of influenza circulation in the community throughout the influenza season should be considered. Oseltamivir (Tamiflu), zanamivir (Relenza), and peramivir (Rapivab) were the antivirals recommended for the 2016–2017 influenza season.19 A generic oseltamivir was approved by the FDA in August 2016, giving patients a less expensive option.25
In patients who are mechanically ventilated or critically ill, oseltamivir may be administered via nasogastric or orogastric (NG/OG) tube. The powder from capsules should be dissolved in 20 mL of Sterile Water and injected down the NG/OG tube, followed by a 10-mL Sterile Water flush.20
– See more at: https://www.uspharmacist.com/article/antiviral-therapy-in-patients-with-influenza#sthash.5hPEtMHF.dpuf
Despite advances in preventive care, infection with the influenza virus sometimes occurs. In such cases, practitioners must be able to quickly identify patients at high risk for developing complications in order to lessen the morbidity and mortality associated with the influenza virus. Some patients may require chemoprophylaxis to prevent infection. The agents for treatment and chemoprophylaxis are the same, and pharmacists should play an active role in ensuring that the correct dosage is used for the correct indication.
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