How does Tamiflu work

Tamiflu is a prescribed antiviral medication used in the treatment and prevention of the flu – how does it work?

Influenza, commonly known as the flu, is a respiratory infection caused by the influenza virus. The flu affects approximately between 10 and 20 percent of the population worldwide. Antivirals are sometimes prescribed for the flu, these medications – such as Tamiflu – work to prevent the virus from replicating in the body.

The infection can be mild or severe and affects the nose, throat, and lungs. Persons with the flu generally experience symptoms such as fever, sore throat, fatigue, muscle aches, or headaches. In comparison to the common cold, the onset of symptoms associated with the flu is sudden. Influenza comes in several subtypes, including types A and B, which are responsible for the seasonal flu epidemics every year. In North America, the flu season is typically between fall and early spring.

The flu virus is contagious and can spread from one person to another. It spreads by tiny droplets coming out from infected individuals when they cough, sneeze, or talk. These droplets can either fall on the nose or mouth of persons nearby. People infected with the flu can generally expect to first experience the symptoms between one and four days and may spread the infection to others before their symptoms begin to develop. 

Infection with Influenza can result in serious health complications. These complications include pneumonia, ear infections, bacterial infections, as well as inflammation of the heart and brain. Children aged five and below, adults over age 65, pregnant women, and individuals with weakened immune systems are considered to be at a high risk of developing these complications from the flu.

A flu vaccine is considered highly effective in helping prevent the flu. According to the Center for Disease Control and Prevention (CDC), the vaccine can help reduce the risk of developing the infection as well as hospitalizations associated with the flu. It is generally recommended for every person aged six months and over to get vaccinated against the flu each year. This is because the flu virus is capable of adapting quickly and the vaccine’s effectiveness generally declines over time, needing the vaccine to be updated every year.

There are several antiviral drugs available to treat the flu. These include oseltamivir, more commonly known by the brand name Tamiflu. The CDC, World Health Organization (WHO), and other public health organizations recommend treating the flu with neuraminidase inhibitors, such as Tamiflu.

How does Tamiflu work?

Tamiflu is an antiviral medication used to treat the symptoms of the flu, caused by influenza virus types A and B. The drug can lower the risk of serious health complications associated with the flu. It can also help prevent the flu; however, it is not considered as a substitute for the flu vaccine.

Tamiflu is a neuraminidase inhibitor – a type of drug that blocks the neuraminidase enzyme that coats the surface of the virus. The neuraminidase enzyme enables the virus to invade the host cell, where it can then replicate. The new virus particles break through the cell membrane of the infected cell and move to neighbouring host cells.

Tamiflu works by binding to the neuraminidase enzyme. This blocks the release of the virus from the infected host cell. The virus is unable to invade other host cells, preventing the spread of the infection in the respiratory tract. The replication of the virus generally peaks between one and three days after infection. It is recommended that doctors prescribe Tamiflu to individuals infected with influenza and showing flu-like symptoms as soon as possible.

How long does it take for Tamiflu to work?

Patients usually experience improvement in their symptoms from initiating the drug within 48 hours of becoming infected with the flu. The medication helps reduce the duration of the infection by one or two days.

There are some studies, suggesting oseltamivir taken around four or five days from the onset of the infection can potentially lessen the symptoms of patients hospitalized for the flu. A 2013 study, published in Lancet Infectious Diseases, suggests that initiating oseltamivir around five days after getting the flu, helped shorten the duration of the infection.

Taking Tamiflu

Tamiflu can be prescribed to persons aged two weeks and older for treating the flu. It can be prescribed to individuals aged one year and older to prevent the flu.

The medication is administered orally and is available in two forms: capsules and oral suspension (supplied as powder). The capsules come in three different sizes (30mg, 45 mg, and 75 mg). Individuals, unable to swallow the capsules, can choose to take the drug in the oral suspension form.

The recommended dosage for adults is generally around 75 mg.  Patients are directed to take the medication twice daily for about five days to treat the flu. They can take the medication to prevent getting the flu once daily for around ten days after coming in contact with an infected person or about six weeks following an outbreak in the community.

Side effects of Tamiflu

Common side effects of Tamiflu include nausea, vomiting, headache, diarrhea, abdominal pain, and dizziness. Other side effects, considered to be rare, include seizures, confusion, hallucinations, abnormal behaviour, gastrointestinal tract bleeding, arrhythmias, hepatitis, and severe skin rash. These side effects are serious and patients experiencing them should stop taking the drug and see a doctor immediately.

Patients allergic to oseltamivir should not take the drug. Tamiflu is not recommended for individuals with end-stage renal disease not undergoing dialysis.

The oral suspension for Tamiflu contains sorbitol and may not be recommended for individuals with hereditary fructose intolerance. They may be at risk of developing diarrhea and indigestion from taking the medication.

Written by Ranjani Sabarinathan, MSc                                                                                      

References

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

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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 randomised placebo-controlled trial. Lancet Infect Dis. 2014 Feb;14(2):109-18. doi: 10.1016/S1473-3099(13)70267-6. Epub 2013 Nov 22. PMID: 24268590.

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