Oseltamivir (Tamiflu)

Generic Name: Oseltamivir

TAMIFLU (oseltamivir phosphate), an influenza neuraminidase inhibitor (NAI), is available as:

  • Capsules containing 30 mg, 45 mg, or 75 mg of oseltamivir for oral use, in the form of oseltamivir phosphate, and
  • A powder for oral suspension, which when constituted with water as directed contains 6 mg per mL oseltamivir base.

In addition to the active ingredient, each capsule contains croscarmellose sodium, povidone K30, pregelatinized starch, sodium stearyl fumarate and talc. The 30 mg capsule shell contains gelatin, red iron oxide, titanium dioxide, and yellow iron oxide. The 45 mg capsule shell contains black iron oxide, gelatin, and titanium dioxide. The 75 mg capsule shell contains black iron oxide, gelatin, red iron oxide, titanium dioxide, and yellow iron oxide. Each capsule is printed with blue ink, which includes FD&C Blue No. 2 as the colorant.

In addition to the active ingredient, the powder for oral suspension contains monosodium citrate, saccharin sodium, sodium benzoate, sorbitol, titanium dioxide, tutti-frutti flavoring, and xanthan gum.

Oseltamivir phosphate is 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 chemical formula is C16H28N2O4 (free base). The molecular weight is 312.4 for oseltamivir free base and 410.4 for oseltamivir phosphate salt. The structural formula is as follows:

TAMIFLU® (oseltamivir phosphate) - Structural Formula  - Illustration

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Oseltamivir is a neuraminidase inhibitor, a competitive inhibitor of influenza's neuraminidase enzyme. The enzyme cleaves the sialic acid which is found on glycoproteins on the surface of human cells that helps new virions to exit the cell. Thus oseltamivir prevents new viral particles from being released.

Oseltamivir is used for the prevention and treatment of influenza caused by influenza A and B viruses. It is on the complementary list of the World Health Organization's List of Essential Medicines, the most important medications needed in a basic health system. Oseltamivir's risk-benefit ratio is controversial.

The most frequent side effects of oseltamivir are:

  • Nausea
  • Vomiting
  • Diarrhea
  • Bronchitis
  • Abdominal pain
  • Headache
  • Dizziness

Administering oseltamivir after meals helps reduce nausea.

Other reported adverse events include:

  • Allergic reactions
  • Skin reactions
  • Seizures
  • Behavioural disturbances
  • Aggravation of diabetes

Adult

Dosage Forms & Strengths

capsule

  • 30mg
  • 45mg
  • 75mg

powder for oral suspension

  • 6mg/mL

Influenza A and B Prophylaxis

75 mg PO qDay for at least 10 days

Dosing considerations

  • Initiate within 48 hours of exposure
  • For community outbreak, may administer for up to 6 weeks

Influenza A and B Treatment

75 mg PO q12hr x5 days

Dosing considerations

  • Initiate within 48 hours of influenza symptom onset

H1N1 Influenza A (Swine Flu) Prophylaxis (Off-label)

75 mg PO qDay

Dosing considerations

  • Postexposure prophylaxis: Initiate within 7 days of exposure and continue for at least 10 days
  • Preexposure prophylaxis (community outbreak): Initiate during potential exposure period and continue for 10 days after last known exposure

H1N1 Influenza A (Swine Flu) Treatment (Off-label)

75 mg PO q12hr x5 days

Dosing considerations

  • Initiate within 48 hours of influenza symptom onset

Dosing Modifications

Renal impairment

  • Treatment
    • CrCl >60 mL/min: No dosage adjustment necessary
    • CrCl >30 to 60 mL/min: 30 mg PO BID
    • CrCl >10 to 30 mL/min: 30 mg PO qDay
    • End-stage renal disease (not undergoing dialysis): Not recommended (not studied)
  • Prophylaxis
    • CrCl >60 mL/min: No dose adjustment necessary
    • CrCl >30 to 60 mL/min: 30 mg PO qDay
    • CrCl >10 to 30 mL/min: 30 mg PO every other day
    • End-stage renal disease (not undergoing dialysis): Not recommended (not studied)

Pediatric

Dosage Forms & Strengths

capsule

  • 30mg
  • 45mg
  • 75mg

powder for oral suspension

  • 6mg/mL

Influenza A and B Prophylaxis

<1 year: Safety and efficacy not established for prophylaxis

≥1 year

  • <15 kg: 30 mg PO qDay x10 days
  • 15-23 kg: 45 mg PO qDay x10 days
  • 23-40 kg: 60 mg PO qDay x10 days
  • >40 kg: 75 mg PO qDay x10 days

Dosing considerations

  • Start within 2 days of exposure

Influenza A and B Treatment

<2 weeks: Safety and efficacy not established for treatment

Aged 2 weeks to <1 year

  • 3 mg/kg PO BID x5 days

≥1 year

  • <15 kg: 30 mg PO q12hr x5 days
  • 15-23 kg: 45 mg PO q12hr x5 days
  • 23-40 kg: 60 mg PO q12hr x5 days
  • >40 kg: 75 mg PO q12hr x5 days

Dosing considerations

  • Start within 24-48 hours of symptom onset

H1N1 Influenza A (Swine Flu) Prophylaxis (Off-label)

<1 year

  • <3 months: Data limited; not recommended unless situation judged critical
  • 3-5 months: 20 mg PO qDay x10 days
  • 6-11 months: 25 mg PO qDay x10 days

≥1 year

  • <15 kg: 30 mg PO qDay x10 days
  • 15-23 kg: 45 mg PO qDay x10 days
  • 23-40 kg: 60 mg PO qDay x10 days
  • >40 kg: Administer as in adults

H1N1 Influenza A (Swine Flu) Treatment (Off-label)

Acute illness and age <1 year

  • <3 months: 12 mg PO q12hr x5 days
  • 3-5 months: 20 mg PO q12hr x5 days
  • 6-11 months: 25 mg PO q12hr x5 days

Acute illness and age ≥1 year

  • <15 kg: 30 mg PO q12hr x5 days
  • 15-23 kg: 45 mg PO q12hr x5 days
  • 23-40 kg: 60 mg PO q12hr x5 days
  • >40 kg: Administer as in adults

Live Attenuated Influenza Vaccine

The concurrent use of TAMIFLU with live attenuated influenza vaccine (LAIV) intranasal has not been evaluated. However, because of the potential for TAMIFLU to inhibit replication of live vaccine virus and possibly reduce the efficacy of LAIV, avoid administration of LAIV within 2 weeks before or 48 hours after TAMIFLU administration, unless medically indicated.

Inactivated Influenza Vaccine

Inactivated influenza vaccine can be administered at any time relative to use of TAMIFLU.

Drugs Without Clinically Significant Drug Interaction With TAMIFLU

No dose adjustments are needed for either oseltamivir or the concomitant drug when coadministering oseltamivir with amoxicillin, acetaminophen, aspirin, cimetidine, antacids (magnesium and aluminum hydroxides and calcium carbonates), rimantadine, amantadine, or warfarin.

Some people using oseltamivir have had sudden unusual changes in mood or behavior, most often in children. It is not certain that oseltamivir is the exact cause. Even without using oseltamivir, anyone with influenza can have neurologic or behavioral effects that may lead to confusion or hallucinations. Call your doctor right away if the person using this medicine has any signs of unusual thoughts or behavior.

Serious Skin/Hypersensitivity Reactions

Cases of anaphylaxis and serious skin reactions including toxic epidermal necrolysis, Stevens-Johnson Syndrome, and erythema multiforme have been reported in postmarketing experience with oseltamivir phosphate capsules. Stop oseltamivir phosphate capsules and institute appropriate treatment if an allergic-like reaction occurs or is suspected. The use of oseltamivir phosphate capsules is contraindicated in patients with known serious hypersensitivity to oseltamivir phosphate.

Neuropsychiatric Events

​There have been postmarketing reports of delirium and abnormal behavior leading to injury, and in some cases resulting in fatal outcomes, in patients with influenza who were receiving oseltamivir phosphate. Because these events were reported voluntarily during clinical practice, estimates of frequency cannot be made but they appear to be uncommon based on oseltamivir phosphate usage data. These events were reported primarily among pediatric patients and often had an abrupt onset and rapid resolution. The contribution of oseltamivir phosphate to these events has not been established. Influenza can be associated with a variety of neurologic and behavioral symptoms that can include events such as hallucinations, delirium, and abnormal behavior, in some cases resulting in fatal outcomes. These events may occur in the setting of encephalitis or encephalopathy but can occur without obvious severe disease. Closely monitor oseltamivir phosphate capsules-treated patients with influenza for signs of abnormal behavior. If neuropsychiatric symptoms occur, evaluate the risks and benefits of continuing oseltamivir phosphate capsules for each patient.

Risk of Bacterial Infections

There is no evidence for efficacy of oseltamivir phosphate capsules in any illness caused by pathogens other than influenza viruses. Serious bacterial infections may begin with influenza-like symptoms or may coexist with or occur as complications during the course of influenza. Oseltamivir phosphate capsules has not been shown to prevent such complications. Prescribers should be alert to the potential for secondary bacterial infections and treat them as appropriate.

Adverse Reactions

The following serious adverse reactions are discussed below and elsewhere in the labeling:
• Serious skin and hypersensitivity reactions.
• Neuropsychiatric events.

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

Adverse Reactions from Treatment and Prophylaxis Trials in Adult and Adolescent Subjects (13 years of age and older)
The overall safety profile of oseltamivir phosphate is based on data from 2,646 adult and adolescent subjects that received the recommended dosage of 75 mg orally twice daily for 5 days for treatment of influenza and 1,943 adult and adolescent subjects that received the recommended dosage of 75 mg orally once daily for up to 6 weeks for prophylaxis of influenza in clinical trials.
The most common adverse reactions in the pooled treatment and pooled prophylaxis trials in adults and adolescents are displayed in Table 5. The majority of these adverse reactions were reported on a single occasion, occurred on either the first or second treatment day and resolved spontaneously within 1-2 days. This summary includes otherwise healthy adults/adolescents and subjects “at risk” (subjects at higher risk of developing complications associated with influenza, e.g., elderly patients and patients with chronic cardiac or respiratory disease). In general, the safety profile in the subjects “at risk” was qualitatively similar to that in otherwise healthy adults/adolescents.

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