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Date of publication:2020/8/19 16:19:46

In October 2018, Food and Drug Administration (FDA) approved baloxavir marboxil (brand name Xofluza) for treatment of early acute uncomplicated influenza in adolescents and adults. This is the first new antiviral flu treatment with a novel mechanism of action approved by the FDA in nearly 20 years. Its one-time dosing and ability to reduce the duration of the flu make Xofluza an attractive option for many patients during flu season. But how does it compare to the popular treatment, Tamiflu (approved in 1999)?

What is influenza?

Compared with COVID-19, influenza is a contagious disease that we are very familiar with. Many people think that influenza is similar to the common cold, but the symptoms of influenza are more severe than common viral colds, which are characterized by rapid onset, epidemic outbreaks, and group illnesses. The main clinical manifestations of influenza include chills, fever (mostly above 38°C), headache, fatigue, nasal congestion, runny nose, sore throat, dry cough, and body aches.

Elderly people, patients with chronic diseases, and physically weak people who are infected with influenza may aggravate other chronic diseases of the patients themselves. Some patients may even develop into severe cases and die due to complications such as acute respiratory distress syndrome, acute necrotizing encephalopathy, and multiple organ dysfunction.

What are Xofluza and Tamiflu?

Xofluza (baloxavir marboxil) and Tamiflu (oseltamivir) are antiviral flu treatments used to shorten the duration of an active flu—specifically flus caused by the influenza A and B viruses. They both work to reduce symptom severity, shorten the duration of symptoms, and lower your risk of being hospitalized.

The active component of XOFLUZA is baloxavir marboxil. The chemical name of baloxavir marboxil is ({(12aR)-12-[(11S)-7,8-Difluoro-6,11-dihydrodibenzo[b,e]thiepin11-yl]-6,8-dioxo-3,4,6,8,12,12a-hexahydro-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazin-7-yl}oxy)methyl methyl carbonate. Its chemical structure is shown below.

baloxavir marboxil chemical structure

The active component of Tamiflu is oseltamivir phosphate, a white crystalline solid with the chemical name (3R,4R,5S)-4-acetylamino-5-amino-3(1-ethylpropoxy)-1-cyclohexene-1-carboxylic acid, ethyl ester, phosphate (1:1). The structural formula is as follows:

Tamiflu structure

Xofluza vs. Tamiflu: Mechanism of Action

Xofluza differs from Tamiflu in its mechanism of action. Tamiflu inhibits the action of the viral enzyme neuraminidase (which lets viruses bud and spread from the infected cell). Xofluza, by contrast, inhibits polymerase acidic endonuclease to prevent viral replication.

Xofluza  mechanism of action
Tamiflu mechanism of action, image source: https://www.nejm.org/

Xofluza mechanism of action, image source: https://www.xofluza.com/

Xofluza vs. Tamiflu: Efficiency

In two randomized trials enrolling more than 1,800 patients, one oral dose of baloxavir significantly reduced the duration of flu symptoms, as well as infectivity/contagiousness (i.e., duration of viral shedding), and viral levels in the upper airway. This was compared to either placebo or oseltamivir.

In patients with influenza type B, Xofluza was found to be particularly more effective than oseltamivir, reducing the time to improvement of symptoms (median 75 hours compared to 102 hours).

Like oseltamivir, Xofluza is to be given in the first 48 hours of flu symptoms. 

Xofluza vs. Tamiflu: Forms and strengths

Tamiflu and Xofluza come in different forms and strengths:

Tamiflu: 20 mg, 45 mg, and 75 mg capsules, and 6 mg/ml powder for oral suspension

Xofluza: 20 mg and 40 mg tablets 

Xofluza vs. Tamiflu: Dosing


To treat an active flu, adults and adolescents 13 years of age and older should take one 75 mg tablet of Tamiflu twice daily for 5 days, or 12.5 ml of the oral suspension twice daily for 5 days. Dosing for pediatric patients 2 weeks of age through 12 years of age will depend on weight and must be determined by a doctor.

In addition to treating the flu, Tamiflu can also be used for flu prevention. The 75 mg tablet is commonly used for flu prevention in those 13 years or older and should be taken once daily for 10 days.


Dosing for Xofluza is based on weight. Adults and adolescents weighing 40 kg to 80 kg should take two 20 mg tablets, and patients weighing at least 80 kg should take two 40 mg tablets.

Unlike Tamiflu, Xofluza cannot be used to prevent the flu.

Xofluza vs. Tamiflu: Side Effects

Tamiflu and Xofluza share some similar side effects such as nausea and headache. Based on clinical trials, Tamiflu may have a higher occurrence of these side effects. Other common side effects of Tamiflu include vomiting and pain, according to the label from the U.S. Food and Drug Administration. Other common side effects of Xofluza include diarrhea, inflammation of the lung airways (bronchitis), and inflammation of the sinuses (sinusitis).

Tamiflu may cause more serious side effects such as skin or hypersensitivity reactions. These allergic reactions can start as rashes and become worse over time. There have also been reports of psychiatric events such as delirium, hallucinations, and abnormal behavior in those taking Tamiflu. These psychiatric events have mostly been reported from children in Japan.

Xofluza may also cause skin or hypersensitivity reactions. These reactions can be experienced as redness or itching. There is also a risk of bacterial infections when taking Xofluza.

Huateng Pharma has worked extensively and developed innovative technologies in the area of API intermediates technology. Our innovative team of chemists has a proven track record in process development, process optimization and scale-up. Whether you're looking for quantities in grams, tons or anything in between, we are ready to provide you with unparalleled levels of service with a proven track record for providing quality product in a timely manner. You can find our baloxavir marboxil intermediates and oseltamivir intermediates in our official website. 

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