Tamiflu (oseltamivir phosphate)

Dosage of oseltamivir phosphate is expressed in terms of oseltamivir.

Oseltamivir phosphate is administered orally without regard to meals, although administration with meals may improve GI tolerability.

Oseltamivir phosphate is commercially available as 30-, 45-, and 75-mg capsules and as a powder for oral suspension that is reconstituted to provide an oral suspension containing 6 mg of oseltamivir per mL.

Reconstituted oseltamivir phosphate oral suspension is preferred for patients who cannot swallow capsules. Alternatively, if the powder for oral suspension is not available from the manufacturer or wholesaler, the appropriate strength of commercially available oseltamivir capsules can be administered by opening the capsules and mixing the contents with a sweet liquid (e.g., regular or sugar-free chocolate syrup, corn syrup, caramel topping, light brown sugar dissolved in water).

During emergency situations if the powder for oral suspension is not available and the appropriate strength of oseltamivir capsules is not available to mix with sweetened liquids, an emergency supply of oseltamivir phosphate oral suspension can be prepared extemporaneously by a pharmacist using the commercially available 75-mg capsules of the drug. (See Extemporaneous Oral Suspensions under Dosage and Administration.)

There is no enhanced messaging for this drug.

Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

Selected Antiviral Agents/Influenza Virus Vaccine Live

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: Amantadine,(1) oseltamivir,(2) rimantadine,(3) zanamivir,(4) and baloxavir,(5) may inactivate the intranasal live influenza virus vaccine, preventing the body from developing an immune response.

CLINICAL EFFECTS: Administration of amantadine,(1) oseltamivir,(2) rimantadine,(3) zanamivir,(4) and baloxavir,(5) may render the intranasal live influenza virus vaccine ineffective.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The US manufacturers of amantadine,(1) oseltamivir,(2) rimantadine,(3) zanamivir(4), baloxavir(5), and the intranasal live influenza virus vaccine(6) state that these agents should not be initiated within 2 weeks of the administration of the intranasal live influenza virus vaccine and that the vaccine should not be administered within 48 hours of the discontinuation of these agents. Inactivated influenza vaccine may be used at any time.(1)

DISCUSSION: Because antiviral drugs such as amantadine,(1) oseltamivir,(2) rimantadine,(3) zanamivir,(4) and baloxavir (5) inhibit the replication of live viruses, these agents may interfere with the efficacy of the intranasal live influenza virus vaccine.

There are no severe interactions for this drug.

There are no moderate interactions for this drug.

There is no enhanced messaging for this drug.

There are no contraindication contraindications for this drug.

• Chronic kidney disease stage 3A (moderate) GFR 45-59 ml/min
• Chronic kidney disease stage 3B (moderate) GFR 30-44 ml/min
• Chronic kidney disease stage 4 (severe) GFR 15-29 ml/min
• Chronic kidney disease stage 5 (failure) GFr<15 ml/min

• Acute cognitive impairment
• Delirium
• Kidney disease with likely reduction in glomerular filtration rate (GFr)
• Suicidal ideation

There is no enhanced messaging for this drug.

Rare or Very Rare

• Abnormal hepatic function tests
• Accidental injury
• Acute cognitive impairment
• Anaphylaxis
• Behavioral disorders
• Cardiac arrhythmia
• Delirium
• Erythema multiforme
• Facial edema
• Gastrointestinal hemorrhage
• Hallucinations
• Hemorrhagic colitis
• Hepatitis
• Hypothermia
• Seizure disorder
• Stevens-johnson syndrome
• Tongue swelling
• Toxic epidermal necrolysis
• Urticaria

More Frequent

• Headache disorder
• Nausea
• Vomiting

Less Frequent

• Diarrhea

Rare or Very Rare

• Agitation
• Allergic dermatitis
• Delusional disorder
• Eczema
• Nightmares
• Pain
• Skin inflammation
• Skin rash
• Symptoms of anxiety

No enhanced messaging available.

No enhanced messaging available.

There are no adequate and well-controlled studies using oseltamivir in pregnant women to inform a drug-associated risk of adverse developmental outcomes. Available published epidemiological data suggest that oseltamivir administered during any trimester of pregnancy is not associated with an increased risk of birth defects; however, these studies had various limitations (e.g., small sample sizes, use of different comparison groups, lack of dosage information) which preclude a definitive assessment of the risk. Although data are insufficient to make a definitive assessment of the risk, prospective and retrospective observational studies that included approximately 5000 women exposed to oseltamivir during pregnancy (including approximately 1000 women exposed during the first trimester) suggest that the observed rate of congenital malformations following oseltamivir exposures during any trimester was not greater than that reported in the general population.

In animal reproduction studies, no adverse embryofetal effects were observed in pregnant rats and rabbits treated with oral oseltamivir at dosages resulting in clinically relevant exposures. There was a dose-dependent increase in the incidence rates of a variety of minor skeletal abnormalities and variants in offspring of rats and rabbits exposed to maternally toxic dosages (approximately 190 and at least 8 times usual human exposure, respectively). No adverse maternal or embryofetal effects were observed in rats exposed to maternally toxic dosages (approximately 44 times usual human exposure).

Pregnant women are at increased risk for severe complications from influenza, which may lead to adverse pregnancy and/or fetal outcomes including maternal death, still births, birth defects, preterm delivery, low birthweight, and small size for gestational age.

Oseltamivir is the preferred antiviral for the treatment of suspected or confirmed influenza or prevention of influenza in women who are pregnant or up to 2 weeks postpartum.

Limited data indicate that oseltamivir and its active metabolite, oseltamivir carboxylate, are distributed into human milk in low concentrations that are considered unlikely to cause toxicity in nursing infants.

The benefits of breast-feeding and the importance of oseltamivir to the woman should be considered along with potential adverse effects on the breast-fed child from the drug or from the underlying maternal condition.

Dosage adjustments are not needed in geriatric patients. (See Geriatric Precautions under Cautions.)