What Is Oseltamivir Phosphate?

Oseltamivir phosphate is an antiviral medication that prevents viruses from successfully replicating using host cells. The first drug developed in the neuraminidase inhibitor class of antivirals, it is used to both prevent and treat influenza. Studies show that the drug’s method of action makes it most effective if treatment is started within the first two days of having the flu. Tamiflu® is the trade name for oseltamivir phosphate, and it is the most widely used antiviral in the world. The substance itself is not active; rather it is converted in the liver to its active antiviral form.

The United States Food and Drug Administration (FDA) has approved oseltamivir phosphate for patients one year and older for treating the flu. Unlike some other antiviral medications, oseltamivir phosphate is effective against both Type A and Type B influenza viruses. The medication is effective if taken within the first 48 hours of showing flu symptoms and generally reduces the duration and severity of the illness. Oseltamivir phosphate is also used to lessen the likelihood of coming down with the flu after exposure to the virus. Although it is used as a preventative, health professionals advise that it is not a substitute for annual flu vaccines.

The medication is available in both capsule and suspension form. Young children and those who have difficulty swallowing capsules are generally given the liquid form. The recommended dose for treatment of the flu in patients who are 13 years and older is 75 milligrams of the medication twice a day for a duration of five days. Doses for children under 13 are determined based on the patient’s weight. For prevention of the flu, the medication is taken for a minimum of 10 days after exposure.

Side effects determined in initial studies of oseltamivir phosphate include nausea, vomiting, abdominal pain and headache. Diarrhea, dizziness and bronchitis are other reported side effects. After the approval of the medication, other adverse reactions have been reported. These include cardiac arrhythmia, abnormal liver functioning and neuropsychiatric events. Abnormal behaviors, hallucinations and incidences of self-harm have been reported in children, adolescents and adults.

Governments have stockpiled oseltamivir phosphate during periods of concern about influenza pandemics. There have also been times when the medication is in short supply due to the limited availability of Chinese star anise, an extract of which is a critical ingredient in the production of the drug. Research into finding alternatives to star anise as a source of shikimic acid, the critical ingredient, continue. Cases of individuals stockpiling oseltamivir phosphate have also been reported, especially when people fear a shortage of the medication might occur.