Amantadine is no longer recommended for treatment of flu virus in the United States. It was only effective against influenza A viruses, but for several years, these viruses have been resistant to amantadine. This means the drug doesn’t work well against these flu viruses.

Medications used to treat the flu virus are called antivirals. These medications are used because they may shorten a case of the flu and reduce your risk of flu complications.

Flu viruses change from season to season and even during a flu season. As viruses go through genetic changes, they can become resistant to certain antiviral medications, like amantadine. Antiviral drugs work by binding to proteins on the surface of viruses. This stops viruses from spreading to healthy cells. When viruses change their proteins, they can become resistant to antivirals.

The Centers for Disease Control and Prevention (CDC) constantly checks flu viruses collected in the United States and around the world for resistance to the recommended antiviral drugs. This is known as domestic and global surveillance.

Although amantadine is no longer used to treat the flu, it is still approved to treat Parkinson’s disease under the brand name Gocovri.

Currently recommended antivirals for flu

There are two types of flu viruses: types A and B. The CDC has recommended four antiviral options that are effective against both type A and B flu viruses for the 2020-2021 flu season:

• Oseltamivir phosphate (Tamiflu) is the most commonly used antiviral for flu. This is an oral drug that can be taken at any age. Common side effects may include nausea, vomiting and headache.
• Zanamivir (Relenza) can be taken by people 7 years and older. This is an inhaled oral drug. It should not be used in people with asthma or chronic obstructive pulmonary disease (COPD). Common side effects include wheezing, sinusitis and dizziness.
• Peramivir (Rapivab) is an intravenous antiviral that can be used at two years old or older. The most common side effect is diarrhea.
• Baloxavir marboxil (Xofluza) is for people 12 and older. It is an oral drug and has no common side effects.

The CDC recommends that your doctor treat you with a flu antiviral as soon as possible if:

• You have flu symptoms and you are in the hospital.
• You have a severe flu that is progressive or causing a complication, such as pneumonia.
• You are at higher risk for flu complications.

Your doctor may still consider treating you even if you don’t fall into one of these groups if it has been less than 48 hours since you started having flu symptoms like fever, sore throat or cough.