Nat-Oseltamivir

Brand Name

Nat-Oseltamivir

Common Name

oseltamivir

In this drug factsheet:

• How does this medication work? What will it do for me?
• How should I use this medication?
• What form(s) does this medication come in?
• Who should NOT take this medication?
• What side effects are possible with this medication?
• Are there any other precautions or warnings for this medication?
• What other drugs could interact with this medication?

How does this medication work? What will it do for me?

Oseltamivir belongs to the family of medications called antivirals. It is used to treat the influenza viruses that cause the flu. It works by inhibiting an enzyme the flu virus needs to spread through your body. If it is used within 2 days of the start of flu symptoms, oseltamivir can reduce the time it takes for flu symptoms to improve by about one day.

Oseltamivir is also used to prevent influenza following close contact with an infected person.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

How should I use this medication?

The recommended adult (13 years of age and above) dose of oseltamivir for treatment of influenza is 75 mg, taken twice a day starting within 2 days of the onset of flu symptoms and continuing for 5 days. It can be taken with or without food. If stomach upset occurs, take it with food.

For children (1 to 12 years) the dosage is based on the body weight of the child. The appropriate dose is taken twice a day.

To prevent influenza, oseltamivir should be started within 2 days of close contact with an infected person, after symptoms start appearing. The usual dose of oseltamivir for the prevention of influenza in adults is 75 mg, taken once a day for 10 days. The dosage for children is based on body weight, taken once a day. Children and seniors should take oseltamivir for at least 10 days, though they may often continue therapy for up to 14 days.

If you are using the liquid form of this medication, use an oral syringe to measure each dose, as it gives a more accurate measurement than household teaspoons. If the liquid is not available, the capsules may be opened and mixed with a small amount of a sweetened liquid, such as chocolate syrup.

Finish all this medication, even if you have started to feel better.

Many things can affect the dose of a medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important that this medication be taken exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature and keep it out of the reach of children. The oral suspension may be stored at room temperature for 10 days from the day of mixing, or in the refrigerator for 17 days from the day of mixing.  Shake well before each use.

Do not dispose of medications in wastewater (e.g. down the sink or in the toilet) or in household garbage. Ask your pharmacist how to dispose of medications that are no longer needed or have expired.

What form(s) does this medication come in?

Capsules

30 mg
Each white-to-off-white, powder-filled, size 4 capsule, with yellow cap imprinted with "30 mg" with blue ink and yellow body imprinted with "NAT" with blue ink, contains 30 mg of oseltamivir as oseltamivir phosphate. Nonmedicinal ingredients: pregelatinized starch, croscarmellose sodium, povidone K30, sodium stearyl fumarate, and talc; capsule shell: gelatin, red iron oxide, yellow iron oxide, and titanium dioxide; blue ink: shellac, propylene glycol, and FD&C Blue No. 2 Aluminum Lake as a colorant.

45 mg
Each white-to-off-white, powder-filled, size 4 capsule, with grey cap imprinted with "45 mg" with blue ink and grey body imprinted with "NAT" with blue ink, contains 45 mg of oseltamivir as oseltamivir phosphate. Nonmedicinal ingredients: pregelatinized starch, croscarmellose sodium, povidone K30, sodium stearyl fumarate, and talc; capsule shell: gelatin, black iron oxide, and titanium dioxide; blue ink: shellac, propylene glycol, and FD&C Blue No. 2 Aluminum Lake as a colorant.

75 mg
Each white-to-off-white, powder-filled, size 2 capsule, with yellow cap imprinted with "75 mg" with blue ink and grey body imprinted with "NAT" with blue ink, contains 75 mg of oseltamivir as oseltamivir phosphate. Nonmedicinal ingredients: pregelatinized starch, croscarmellose sodium, povidone K30, sodium stearyl fumarate, and talc; capsule shell: gelatin, black iron oxide, red iron oxide, yellow iron oxide, and titanium dioxide; blue ink: shellac, propylene glycol, and FD&C Blue No. 2 Aluminum Lake as a colorant.

Powder for Oral Suspension

6 mg/mL
Each bottle of white-to-off-white granular powder blend for reconstitution to a white-to-off-white tutti-frutti-flavoured suspension, contains 390 mg of oseltamivir as oseltamivir phosphate, which when reconstituted, contains 65 mL of suspension at a final concentration of 6 mg/mL of oseltamivir. Nonmedicinal ingredients: monosodium citrate, saccharin sodium, sodium benzoate, sorbitol, titanium dioxide, tutti-frutti flavouring, xanthan gum, and colloidal silicon dioxide.

Who should NOT take this medication?

Do not use this medication if you are allergic to oseltamivir or any ingredients of the medication.

Do not give this medication to children less than 1 year old.

What side effects are possible with this medication?

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• abdominal pain
• headache
• nausea
• vomiting

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not check with your doctor or seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• signs of liver damage (e.g., yellowing of skin or whites of eyes, abdominal pain, loss of appetite, dark urine, light-coloured stools, tiredness, or weakness)

Stop taking the medication and seek immediate medical attention if any of the following occur:

• delirium, confusion, abnormal behavior leading to self-injury, delusions, hallucinations, agitation, anxiety, nightmares
• symptoms of a severe allergic reaction such as rash, itching, flushing, swelling, breathing difficulties, facial swelling, and dizziness
• signs of a severe skin reaction (e.g., blistering, peeling, a rash covering a large area of the body, a rash that spreads quickly, or a rash combined with fever or discomfort)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Are there any other precautions or warnings for this medication?

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Effectiveness: The benefit of oseltamivir has not been evaluated for the treatment of flu symptoms that have been present for more than 2 days.

Flu shots: Oseltamivir is not a substitute for the flu shot. Continue to receive an annual flu shot as advised by your doctor.

Fructose intolerance: The liquid suspension form of this medication contains sorbitol, making it inappropriate for people with hereditary fructose intolerance. If you have fructose intolerance, you should not take the liquid form of oseltamivir. 

Kidney function: Kidney disease or reduced kidney function may cause this medication to build up in the body, causing side effects. If you have reduced kidney function or kidney disease, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Liver function: Oseltamivir may also cause decreased liver function, and liver failure in rare cases. If you experience symptoms of liver problems such as fatigue, feeling unwell, loss of appetite, nausea, yellowing of the skin or whites of the eyes, dark urine, pale stools, abdominal pain or swelling, and itchy skin, contact your doctor immediately.

Neurological effects: There have been rare reports of people who have experienced neurological and psychological problems while taking oseltamivir. These included hallucinations, delusions, delirium, abnormal behaviour, and self-injury. If you experience any of these symptoms, seek immediate medical attention. If you have any concerns about this medication, contact your doctor.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: This medication passes into breast milk. If you are breast-feeding and are taking oseltamivir, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding. Those who are breast-feeding children under 1 year of age should not take this medication.

Children: The safety and effectiveness of using this medication have not been established for children under one year of age.

What other drugs could interact with this medication?

There may be an interaction between oseltamivir and any of the following:

• influenza virus nasal spray vaccine
• clopidogrel
• leflunomide
• probenecid
• teriflunomide

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.

All material copyright MediResource Inc. 1996 – 2025. Terms and conditions of use (opens in a new window). The contents herein are for informational purposes only. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Source: www.medbroadcast.com/drug/getdrug/Nat-Oseltamivir (opens in a new window)