Oseltamivir Phosphate

Medically Reviewed by Dr. Harshi Dhingra, M.D.

Last Reviewed: Jul 07, 2023

Warnings

Oseltamivir Phosphate (Tamiflu) Risks, Warnings, and Complications

Oseltamivir can cause or worsen health problems in some people. Talk to your doctor or pharmacist about other ways to treat flu symptoms if you are at an increased risk of adverse reactions or complications from this medication. Some of the risks of taking oseltamivir include:

ALLERGIC REACTIONS: There are reports of anaphylaxis (throat closing) and serious skin reactions after taking oseltamivir. Call your doctor immediately or seek emergency medical care if you develop signs and symptoms of an allergic reaction, such as rash, hives, itching, swelling of the face or tongue, or difficulty breathing or swallowing. Tell your doctor if you have a history of hypersensitivity to this medicine.
UNUSUAL BEHAVIOR: A small number of people, especially children, have developed unusual behavior, such as delirium, after taking oseltamivir. This abnormal behavior can lead to injuries that may be fatal in some cases. The unusual behaviors can start and stop suddenly. It is unclear if oseltamivir is responsible for these events because flu viruses themselves can be associated with neurologic and behavioral symptoms such as delirium and hallucinations. Call your doctor without delay if you notice any abnormal behavior early during treatment with this medicine.
RISK OF SECONDARY BACTERIAL INFECTIONS: Tamiflu capsules and oral suspension cannot treat illnesses caused by pathogens other than the influenza A and B viruses. Sometimes, serious bacterial infections cause influenza-like symptoms or occur as complications of influenza. Tell your doctor if you have worsening or new symptoms of infection such as fever, chills, cough, sore throat, nasal congestion, runny nose, headache, or body ache during treatment with this medicine.
PATIENTS WITH HEREDITARY FRUCTOSE INTOLERANCE: Oseltamivir oral suspension is sweetened with sorbitol. One 75 mg dose of the oral suspension contains 2 grams of sorbitol, which is above the recommended daily maximum limit of sorbitol for patients with a medical condition called hereditary fructose intolerance. Tell your doctor if you have hereditary fructose intolerance. Your doctor may recommend against taking the oral suspension, which may lead to dyspepsia and diarrhea.

Precautions Before Starting Oseltamivir Phosphate (Tamiflu)

Tell your doctor if you have ever had an allergic reaction to oseltamivir phosphate, any of the active or inactive ingredients in oseltamivir capsules or oral suspension, or any other drugs. Your pharmacy can give you a list of ingredients.

Give your doctor and pharmacist a complete list of your medications, including prescription medications, over-the-counter medicines, dietary supplements, vitamins, and herbal remedies. This can help avoid possible drug interactions between oseltamivir phosphate and your other medications.

Give your doctor a complete medical history. Oseltamivir phosphate may not be right for people with certain medical conditions, such as human immunodeficiency virus (HIV) and AIDS, lung disease, heart disease, kidney disease, or hereditary fructose intolerance. There is no clinical data about the safety and efficacy of this medicine in people with respiratory disease or chronic cardiac disease.

Tell your health care professional if you have previously taken oseltamivir to prevent or treat flu symptoms.

Inform your doctor if you are pregnant, may be pregnant, are planning a pregnancy in the near future, or are nursing an infant with breast milk. Keep in mind that pregnant women are at a higher risk of complications from an influenza infection, including adverse outcomes such as preterm delivery, low birth weight, birth defects, and stillbirth.

Precautions During Use of Oseltamivir Phosphate (Tamiflu)

Keep all your healthcare appointments during treatment for flu symptoms with oseltamivir. Call your doctor if you develop any worsening or new symptoms.

People taking this medicine, especially children and adolescents who have the flu, may develop unusual behavior or symptoms such as confusion, agitation, anxiety, hallucinations, seizures, and thoughts of harming or killing themselves. These symptoms can develop even if you are not taking oseltamivir if you have the flu. Watch carefully for any unusual behavior and call the doctor immediately if it occurs. Family members and caregivers should know which symptoms to look for and how to contact the doctor if the person taking the medicine is unable to call their doctor themselves.

Talk to your doctor about receiving the annual flu shot, which is recommended for all healthy adults, children, and babies 6 months of age and older. Oseltamivir cannot replace early influenza vaccination as a preventive measure. Tell your doctor if you have already received or will receive FluMist (intranasal flu vaccine). Oseltamivir can make this type of flu vaccine less effective if you take the medicine up to 2 days before or 2 weeks after you get the vaccine.

Tell your doctor if you become pregnant while taking oseltamivir.

Tell all your healthcare providers you are on oseltamivir, especially if you are having a procedure, including dental procedures.

Oseltamivir Phosphate (Tamiflu) Drug Interactions

Other drugs can affect how oseltamivir phosphate works. Possible interactions with other medicines can increase the risk of severe adverse effects.

The following medications can have interactions with oseltamivir phosphate:

Cancer chemotherapy drugs
Antimetabolites such as methotrexate (Rheumatrex)
Drugs that affect the immune system, such as azathioprine (Imuran), cyclosporine (Neoral, Sandimmune), sirolimus (Rapamune), and tacrolimus (Prograf)
Oral steroids such as prednisone (Deltasone), dexamethasone (Decadron, Dexone), and methylprednisolone (Medrol)

Give your doctor or pharmacist a complete list of your medications, including prescription drugs, nonprescription drugs, dietary supplements, and herbal remedies to prevent potentially dangerous interactions. Also, tell your healthcare professional if you smoke, drink alcohol, or use recreational drugs because some of these substances can cause serious health complications when used with prescription medications.

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