Oseltamivir (Tamiflu®)

Section 1.1

Midwives may independently prescribe, order and administer this drug.

Neuraminidase inhibitors anti-viral agents oseltamivir (Tamiflu®) and zanamivir (Relenza®) are moderately effective for the treatment of infections with susceptible viruses of influenza strains including H1N1. More safety data is available on oseltamivir than zanamivir in pregnancy. Thus oseltamivir is the treatment of choice for the prevention and treatment of influenza. Oseltamivir reduces the spread of influenza by blocking the action of the enzyme neuraminidase and prevents the spread of virus from cell to cell reducing the duration and severity of symptoms particularly when treatment is initiated early after onset of symptoms. The neuraminidase inhibitors also reduce the duration of shedding and viral titer.

Indications and Clinical Use:

Oseltamivir is recommended during pregnancy when influenza-like illness(ILI) develops, especially those in their second and third trimesters or within 2-4 weeks post-partum. There are significant increased risks for morbidity and mortality related to influenza infection during pregnancy. ILI is defined as the acute onset of respiratory illness with fever and cough and one or more of the following: sore throat, muscle pain, joint pain, exhaustion or prostration. Treatment is most effective if started early, within 48 hours of illness onset, however initiating treatment after 48 hours may still be worthwhile if the illness is progressive in severity. On average, oseltamivir may reduce the duration of symptoms by one and a half days.

Prompt initiation is recommended in initiation of antiviral therapy for individuals with suspected or confirmed influenza infection and any of the following:

  • Illness requiring hospitalization
  • Progressive, severe, or complicated illness, regardless of previous health or vaccination status
  • During pregnancy and up to two weeks postpartum

Treatment should not be delayed while awaiting the results of diagnostic testing, nor should it be withheld in patients with indications for therapy who present >48 hrs after the onset of symptoms, particularly among patients requiring hospitalization. Patients with a negative rapid antigen test for influenza whom present with symptoms that are progressive in severity should be treated with antivirals since the sensitivity of these tests is generally low.

In addition, instructions to remain hydrated and manage fever with acetaminophen should be provided.

Those who are pregnant or postpartum recovering from influenza generally do not require antiviral therapy. The decision to initiate antiviral therapy should be based on the clinician’s judgment and on what is known about the potential benefits of therapy for seasonal influenza versus the potential risks.

Patients with mild uncomplicated influenza infections who do not have risk factors for severe or complicated illness are not likely to benefit from antiviral therapy if it is initiated more than 48 hours after symptom onset.

Given concerning trends of increasing resistance with neuraminidase inhibitors, the risk of promoting antiviral drug resistance should be considered. Overuse of neuraminidase inhibitors will promote further development of resistance and could lead to these agents becoming ineffective.

Contraindications:

Known allergy to any antiviral component; previous severe reactions and/or allergic reactions such as difficulty breathing; tightness in the chest; wheezing; hives; confusion; hallucinations. Zanamivir is administered by oral inhalation and is contraindicated in patients with underlying asthma or other chronic respiratory conditions.

Warnings and Precautions:

Information about the increased risk of complications with influenza illness during pregnancy should be provided, including H1N1 virus, and the need for a prompt assessment. This is especially important information for those who are pregnant and have young children with ILI.

Pregnancy:

Compatible – Limited reports during human pregnancy do not suggest a significant risk of developmental toxicity.  Maternal benefit outweighs the unknown risk if any to the embryo or fetus.

Lactation:

Category L2 – Limited Data – Probably Compatible

Due to breastmilk’s anti-infective benefits and the low dosages of antiviral passed through breastfeeding, it is recommended that breastfeeding be continued when taking antiviral medications. Oseltamivir is not usually prescribed for administration to children under one year of age.

If a significant infection including H1N1 is confirmed or strongly suspected, consultation with a physician is required, even if antiviral therapy has been commenced unless otherwise indicated by a symptom-based protocol established between the midwives and physician consultants in a given community.

In a pandemic situation, how the consultation process takes place may be guided by this specific community-based protocol that take into account the severity of the signs and symptoms and available medical resources.

Based on such protocols, the midwife should do an assessment to determine if referral for a telephone assessment by a physician, or an in-person physician assessment or an immediate referral for hospital admission is required.

If a specific infection has not been confirmed by a positive swab, advise that if another ILI develops, a second course of antiviral therapy may be recommended because immunity to infection cannot be documented.

Adverse Reactions:

Nausea, vomiting, diarrhea, bronchitis, abdominal pain, headache and dizziness.

There are no known interactions between oseltamivir and other drugs. Oseltamivir does not interact with the flu vaccine so both vaccinated and unvaccinated individuals can use oseltamivir.

Tamiflu® may increase the risk for self-injury and confusion in people who have the flu.

Any odd behaviour should be reported.

Please refer to the website below for a list of Reportable Adverse Reactions to Antiviral Drugs.

Dosage and Administration:

Oseltamivir (Tamiflu®): One 75 mg capsule orally every 12 hours (bid) for 5 days or prescribe Zanamivir if nausea and vomiting.
Zanamivir (Relenza®): Two 5 mg inhalations (10 mg total) every 12 hours (bid) for 5 days. More information can be located in the appropriate product monograph.
May be after meals to reduce nausea.

Dose reduction is advised for pharmacokinetic reasons when creatinine clearance of <10 ml/min is present.