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Influenza

Conventional Flu Treatment

Treatment of the flu typically aims to ease symptoms and prevent complications. In many cases, over-the-counter medicines can relieve symptoms such as aches and fever. However, this approach may not be sufficient for those at high risk for flu-related complications. In high-risk cases, such as hospitalized people with severe illnesses, antiviral therapy is employed (MD Consult 2012).

The decision to initiate antiviral drug therapy for the treatment of influenza depends on a number of factors, such as individual patient characteristics, the time elapsed since symptoms began, as well as the prevalence and virulence of influenza circulating in the surrounding community (Afilalo 2012; Fiore 2008; Ebell 2005). The goal of treatment with antiviral drugs is to reduce signs and symptoms of influenza and prevent hospitalizations or death in patients with severe disease (Hsu 2012).

The antiviral drugs most commonly used to treat influenza include neuraminidase inhibitors (eg, oseltamivir [Tamiflu®] and zanamivir [Relenza®]) and adamantanes (eg, amantadine [Symmetrel®] and rimantadine [Flumadine®]).

  • Neuraminidase inhibitors interfere with viral neuraminidases, which promote viral infection of healthy cells, drive inflammation, and mitigate viral inactivation by respiratory mucus (MD Consult 2011). They produce gastrointestinal side effects such as nausea and vomiting in about 10% of those who take them and have rarely been reported to cause bronchospasm in asthmatics (MD Consult 2007). They should be administered within 24-48 hours of onset of symptoms.
  • Adamantanes are thought to exert antiviral action by inhibiting the release of viral genetic material into the host cell via interfering with uncoating of the virus particle (MD Consult 2009). These drugs can cause potentially serious side effects, such as heart rhythm irregularities, hallucinations, and respiratory distress, especially in the elderly or those with impaired kidney function (MD Consult 2007). Over recent years, the CDC has made recommendations for or against use of adamantaes for treatment or prevention of the flu, depending on which strain is actively circulating in the population. For example, during the 2005–06 flu season and 2009 H1N1 outbreak, the CDC recommended against the use of adamantanes (CDC 2006; CDC 2011f).

Patients infected with a highly pathogenic (such as, H5N1) or resistant form of influenza may be prescribed the antiviral drug ribavirin (eg, Copegus®, Rebetol®, Virazole®) (Fediakina 2011). Ribavirin, although not directly indicated for influenza, has multiple potential clinical applications (due to its broad spectrum antiviral activity) and has been used to treat influenza on a limited basis (Razonable 2011; Schleiss 2011; Beigel 2008). Adverse effects of ribavirin may include nausea, joint and muscle pain, bone marrow depression, heart rhythm irregularities, and pancreatitis (MD Consult 2007).

One of the most important things to know before taking antiviral drugs is how long it has been since the onset of influenza-like symptoms. In general, antiviral drug treatment should be started within 48 hours of symptom onset (MMWR 2012); clinical studies have demonstrated little benefit when these agents are given outside this time window (Fiore 2008). However, results of a survey of patients at an internal medicine clinic showed only 13% reported calling their physician within 48 hours after initial onset of symptoms (Gaglia 2007).

The CDC recommends that antiviral drug treatment only be used in select patient populations (CDC 2011b). This may be because most cases of seasonal influenza are self-limiting (NIH 2008), because antiviral drugs can cause side effects, and because the drugs are only capable of decreasing symptoms by 1 day among healthy individuals (Bijl 2011). However, individuals who are hospitalized, severely ill, or at high risk of infection should be treated with an antiviral drug within 48 hours of symptom onset. High-risk groups may include children <2 years and adults ≥65 years, the immunocompromised, the morbidly obese (ie, Body Mass Index [BMI] ≥40), and long-term care residents. High-risk groups may also be prescribed antiviral drugs on a preventive basis. Although antiviral medications are between 70–90% effective for preventing influenza infections, they should not be used capriciously because they can promote the emergence of resistant viral strains (CDC 2011b). Since influenza is caused by a virus and not a bacterium, taking antibiotics is not recommended and could lead to unwanted side effects and/or a future antibiotic-resistant infection (CDC 2012a).