Xofluza has an average elimination half-life of about 79 hours, or roughly 3.3 days. That means it takes approximately 4 to 5 half-lives for the drug to clear your system almost entirely, putting the total clearance window at around 13 to 17 days after your single dose. Most of the drug’s activity, however, plays out in the first few days.
How Xofluza Is Processed in Your Body
After you swallow Xofluza, enzymes in your gut, liver, and blood rapidly convert the pill into its active form. This active compound reaches peak levels in your bloodstream within about 4 hours. From there, your liver breaks it down primarily through a specific enzyme pathway, with a minor assist from a second pathway.
Your body gets rid of the drug mostly through stool: about 80% of a dose is excreted that way, with roughly 15% leaving through urine. Because the half-life is long (averaging 79 hours), the drug lingers at measurable levels for well over a week, even though you only take it once.
Why the Long Half-Life Matters
Xofluza was designed to work as a single-dose treatment, and the extended half-life is what makes that possible. One pill keeps active drug circulating long enough to suppress the flu virus across its most critical replication window. In clinical trials, patients who took Xofluza stopped shedding infectious virus within about two days, which is 2 to 3 days faster than placebo and notably faster than the standard five-day course of oseltamivir (Tamiflu), where patients typically remained infectious for 4 to 5 days.
For symptom relief, both Xofluza and oseltamivir shorten illness by at least 23 hours compared to no treatment. The bigger difference is in how quickly you stop being contagious to others.
Factors That Can Affect Clearance
The 79-hour half-life is an average from healthy adults. Individual variation exists: in the FDA’s review, the coefficient of variation was about 22%, meaning some people clear the drug somewhat faster or slower. Body weight also plays a role indirectly, since the dose itself is weight-based. Adults and children weighing 20 to 80 kg (roughly 44 to 176 pounds) take a 40 mg dose, while those at or above 80 kg take 80 mg. A higher dose means more drug to clear, though the half-life itself stays similar.
Liver function matters too, since that’s where the drug is metabolized. No specific adjustments are listed for mild liver impairment, but anyone with significant liver disease may process the drug differently.
Foods and Supplements That Interfere
One important practical detail: Xofluza binds to certain minerals and becomes less effective when taken alongside them. You should avoid dairy products, calcium-fortified drinks, antacids, and supplements containing calcium, iron, magnesium, selenium, or zinc around the time you take your dose. The drug forms a chemical bond with these minerals that lowers how much active drug reaches your bloodstream. Since Xofluza is a single-dose medication, getting the full effect of that one pill is critical.
Timeline at a Glance
- Peak blood levels: roughly 4 hours after taking the dose
- Half-life: about 79 hours (3.3 days), meaning half the drug is gone by then
- Virus shedding stops: within about 2 days for most patients
- Substantially cleared: 13 to 17 days, when less than 5% of the original dose remains
If you’re wondering about Xofluza for a drug test or a medical procedure, the relevant number is that 13-to-17-day window. For practical purposes like returning to work or gauging when you’re no longer contagious, the first 2 to 3 days after your dose are when the drug does most of its heavy lifting against the virus.