Understanding Influenza: The Flu

What is Influenza?

Influenza, commonly referred to as the flu, is a respiratory infection caused by the influenza virus. It affects approximately 10 to 20 percent of the global population each year. Antiviral medications, such as Tamiflu, are sometimes prescribed to prevent the virus from replicating within the body.

Symptoms and Severity

The flu can range from mild to severe, impacting the nose, throat, and lungs. Common symptoms include fever, sore throat, fatigue, muscle aches, and headaches. Unlike the common cold, flu symptoms typically present suddenly. Influenza consists of several subtypes, with types A and B being responsible for seasonal flu epidemics annually.

Flu Season and Transmission

In North America, the flu season usually occurs from fall to early spring. The flu virus is highly contagious, spreading through tiny droplets expelled by infected individuals when they cough, sneeze, or talk. These droplets can land on the mouths or noses of nearby people. Individuals infected with the flu may start experiencing symptoms between one to four days after infection and can transmit the virus to others even before showing symptoms.

Complications and High-Risk Groups

Infection with influenza can lead to serious health complications, including pneumonia, ear infections, bacterial infections, and inflammation of the heart and brain. Certain groups, such as children under five, adults over 65, pregnant women, and those with weakened immune systems, are at higher risk for these complications.

Preventing Influenza: Vaccination and Antivirals

The Importance of Vaccination

The flu vaccine is considered highly effective in preventing the influenza virus. According to the Centers for Disease Control and Prevention (CDC), the vaccine significantly reduces the risk of infection and associated hospitalizations. It is recommended for everyone aged six months and older to receive the vaccine annually due to the virus’s ability to adapt and the vaccine’s declining effectiveness over time.

Antiviral Medications

Several antiviral drugs are available to treat the flu, including oseltamivir, commonly known by its brand name, Tamiflu. Both the CDC and the World Health Organization (WHO) advocate for the use of neuraminidase inhibitors like Tamiflu for flu treatment.

How Tamiflu Works

Tamiflu is an antiviral medication designed to alleviate symptoms caused by influenza virus types A and B. It reduces the risk of serious complications associated with the flu and can also help prevent infection, although it is not a substitute for the flu vaccine. As a neuraminidase inhibitor, Tamiflu blocks the neuraminidase enzyme on the virus’s surface, preventing the virus from invading host cells and spreading throughout the respiratory tract.

Timing and Efficacy of Tamiflu

Tamiflu is most effective when administered within 48 hours of symptom onset. Patients may experience symptom relief and a reduced duration of illness by one or two days. Some studies suggest that administering oseltamivir even four to five days after infection can still lessen symptoms in hospitalized patients.

Administration and Side Effects of Tamiflu

Dosage and Forms

Tamiflu can be prescribed for individuals aged two weeks and older for treating influenza and for those aged one year and older for prevention. The medication is taken orally and comes in two forms: capsules and oral suspension. Capsules are available in three sizes (30 mg, 45 mg, and 75 mg), while the oral suspension is an option for those unable to swallow capsules. The typical dosage for adults is 75 mg, taken twice daily for about five days for treatment and once daily for around ten days for prevention.

Common and Serious Side Effects

Common side effects of Tamiflu include nausea, vomiting, headache, diarrhea, abdominal pain, and dizziness. Rare but serious side effects can include seizures, confusion, hallucinations, abnormal behavior, gastrointestinal bleeding, arrhythmias, hepatitis, and severe skin rashes. Patients experiencing severe side effects should discontinue use and consult a doctor immediately. Individuals allergic to oseltamivir or those with end-stage renal disease not undergoing dialysis should avoid this medication.

Considerations for Oral Suspension

The oral suspension of Tamiflu contains sorbitol, which may not be suitable for individuals with hereditary fructose intolerance, as it can lead to gastrointestinal issues.

References

Tagarro A, Cruz-Cañete M, Otheo E, Launes C, Couceiro JA, Pérez C, Alfayate S; Grupo de trabajo de Infecciones Respiratorias de la SEIP. Oseltamivir para el tratamiento de la gripe en niños y adolescentes. An Pediatr (Barc). 2019 May;90(5):317.e1-317.e8. doi: 10.1016/j.anpedi.2019.01.009.

Key Facts About Influenza (Flu). Retrieved from https://www.cdc.gov/flu/about/keyfacts.htm

Key Facts About Seasonal Flu Vaccine. Retrieved from https://www.cdc.gov/flu/prevent/keyfacts.htm

Tamiflu prescribing information. Retrieved from https://www.gene.com/download/pdf/tamiflu_prescribing.pdf

Moscona A. Neuraminidase inhibitors for influenza. N Engl J Med. 2005 Sep 29;353(13):1363-73. doi: 10.1056/NEJMra050740.

Sur M, Lopez MJ, Baker MB. Oseltamivir. [Updated 2020 Oct 5]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK539909/

Fry AM, Goswami D, Nahar K, Sharmin AT, Rahman M, Gubareva L, Azim T, Bresee J, Luby SP, Brooks WA. Efficacy of oseltamivir treatment started within 5 days of symptom onset to reduce influenza illness duration and virus shedding in an urban setting in Bangladesh: a randomized placebo-controlled trial. Lancet Infect Dis. 2014 Feb;14(2):109-18. doi: 10.1016/S1473-3099(13)70267-6.