To treat flu: Symmetrel (Amantadine), Flumadine (Rimantadine), Tamiflu (Oseltamivir), Relenza (Zanamivir).

To prevent flu: Symmetrel (Amantadine), Flumadine (Rimantadine), Tamiflu (Oseltamivir). Zanamivir is not currently approved for preventive use.

Used against influenza type A: Symmetrel (Amantadine), Flumadine (Rimantadine), Tamiflu (Oseltamivir), Relenza (Zanamivir).

Used against influenza type B: Tamiflu (Oseltamivir), Relenza (Zanamivir).

Dosage forms

* Amantadine and Rimantadine are taken orally in pill form.
* Tamiflu, the first neuraminidase inhibitor in pill form. It is also available as liquid suspension for children.
* Zanamivir is administered by inhalation. Zanamivir can be inhaled using a device known as a Diskhaler.

Age

* Zanamivir is used for people age 7 and older.
* Oseltamivir is used to treat flu in people age 1 and older; to prevent flu in adults and children age 13 and older.
* Amantadine is used in adults and in children older than age 1.
* Rimantadine is used to prevent and treat type A influenza in adults and children age 1 and older.

Possible Side Effects

Side effects differ widely for each antiviral medication. The neuraminidase inhibitors generally cause fewer side effects than the older flu drugs.

Amantadine: The most common side effects associated with Amantadine relate to the nervous and gastrointestinal systems. Elderly people are especially sensitive to the effects of Amantadine. Amantadine may cause light-headedness, difficulty concentrating, dizziness, nervousness, insomnia, confusion, loss of balance, and seizures. Elderly patients often have reduced renal function and are better treated with Rimantadine, which is 75% metabolized by the liver.

Rimantadine: CNS effects like light-headedness, dizziness, headache, difficulty concentrating, nervousness, insomnia, loss of balance, and seizures. Side effects occur less often with Rimantadine than Amantadine.

Zanamivir: Some people who have asthma or chronic obstructive pulmonary disease (COPD) and use Zanamivir may experience reduced lung function and have difficulty breathing. Other side effects usually do not need medical attention, and may go away as your body adjusts to the medicine.

Oseltamivir: The most frequent side effects are nausea, vomiting, diarrhea. These symptoms are mostly mild to moderate and generally occurred within the first two days of administration of the drug.

None of these drugs is recommended for use during pregnancy or nursing. These drugs have not been evaluated in pregnant women.

Cost

Both drugs Amantadine and Rimantadine are available as generic. Oseltamivir and Zanamivir are new medications and are available only as brand name drugs. Therefore, of the four antiviral flu medications, Zanamivir and Oseltamivir are the most expensive.

Conclusions

Amantadine and Rimantadine are of limited use today due to side effects and the rapid appearance of resistant virus that can be spread to close contacts. Furthermore, Amantadine is associated with several drug interactions (with antihistamines or other medications that stimulate the central nervous system) that may increase the risk of side effects such as insomnia, anxiety, and seizures. Also they are only effective against influenza A, a less dangerous form of flu than influenza B.

Oseltamivir and Zanamivir have fewer side effects and may be used as a treatment and post-exposure prophylaxis of both A and B influenza. Additionally, they are better structured to treat and prevent mutating virus strains. Oseltamivir, that has recently become famous as an effective treatment for bird flu, is an orally administered drug and is more convenient to use than the inhaled administrated Zanamivir.