Relenza vs Tamiflu

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For patients diagnosed with influenza, the antiviral medications Relenza and Tamiflu have been shown to effectively reduce the severity and duration of flu symptoms. Both drugs work by inhibiting an enzyme (neuraminidase) that is critical for the replication of influenza virus within a host body – thus lessening the viral load. However, these two drugs differ in their mode of administration and side effects profile. Relenza (Zanamivir) is administered via inhalation which makes it more suitable for older children and adults but not recommended for people with respiratory diseases like asthma or chronic obstructive pulmonary disease (COPD). On the other hand, Tamiflu (Oseltamivir) can be taken orally making it accessible to a wider range of patients including infants over 2 weeks old; although gastrointestinal upset has been reported as one common side effect.

What is Relenza?

Zanamivir (the generic name for Relenza) was one of the first neuraminidase inhibitors approved by the FDA in 1999. It disrupted a major development within antiviral medications, which marked it as distinctive from prior treatments such as amantadine and rimantadine that were no longer effective due to resistance. Zanamivir works by blocking the action of viral neuraminidase, an enzyme that releases viruses from infected cells so they can spread throughout the body. It is prescribed primarily for the treatment and prevention of influenza A and B.

Relenza has a selective influence on viral neuraminidase with minimal systemic absorption, which results in having fewer side effects than other antiviral drugs like Oseltamivir (Tamiflu) which are absorbed systemically and therefore may have stronger effects on other systems within the body. However, Relenza must be administered via inhalation while Tamiflu can be taken orally - an important factor when considering patient compliance or ability to inhale medication effectively.

What conditions is Relenza approved to treat?

Relenza has been approved for the treatment and prevention of certain types of influenza:

  • Influenza A and B: Relenza is used to treat symptoms caused by these viruses in people 7 years of age or older who have had symptoms for no more than two days.
  • Prevention of influenza A and B: It can also be used to prevent flu in people one year old or older.

How does Relenza help with these illnesses?

Relenza helps manage and combat the influenza virus by inhibiting the action of neuraminidase, an enzyme found on the surface of influenza viruses. This enzyme allows newly formed viruses to detach from infected cells and spread throughout the body. By blocking neuraminidase, Relenza prevents new viral particles from leaving infected cells, thus limiting the spread of infection in your body. Just like how serotonin plays a crucial role in mood regulation, neuraminidase is vital for flu virus propagation. Similar to Prozac increasing serotonin levels to mitigate depression symptoms, Relenza inhibits neuraminidase activity to control flu progression and alleviate associated symptoms.

What is Tamiflu?

Tamiflu, or oseltamivir, is a neuraminidase inhibitor that works by blocking the action of viral neuraminidase enzyme. This prevents the influenza virus from spreading within your body, effectively reducing the duration and severity of flu symptoms. Tamiflu was first approved by FDA in 1999 for treating influenza A and B in patients one year or older who have had flu-like symptoms for less than two days. Unlike Relenza which is administered via inhalation, Tamiflu comes as an orally administered capsule or liquid suspension making it simpler to use especially for those with respiratory problems. Furthermore, while both are used to shorten illness length when taken soon after symptom onset, only Tamiflu has been approved as a preventive measure against influenza following exposure to someone with the virus - showcasing its broader application scope compared to Relenza. Its side effects may include nausea and vomiting; however these can be mitigated if taken with food.

What conditions is Tamiflu approved to treat?

Tamiflu is authorized for the treatment of conditions such as:

  • Influenza A and B in people aged two weeks and older
  • Prophylaxis, or prevention, of influenza in people one year of age and older

It's important to note that Tamiflu is most effective if started within 48 hours of onset of flu symptoms.

How does Tamiflu help with these illnesses?

Tamiflu, known generically as oseltamivir, is an antiviral medication that inhibits the action of influenza viruses types A and B in the body. This agent interrupts viral replication by blocking the enzyme neuraminidase, which allows newly formed virus particles to leave infected cells and spread within the body. Tamiflu can both prevent flu infection after exposure and reduce symptoms for those already ill with flu. While Relenza also works on these principles, its use is typically limited because it must be inhaled rather than taken orally like Tamiflu. In this regard, patients often find Tamiflu more convenient and easier to administer especially for children or people with breathing problems where using an inhaler might be challenging or ineffective.

How effective are both Relenza and Tamiflu?

Both zanamivir (Relenza) and oseltamivir (Tamiflu) have been recognized as effective antiviral drugs against influenza virus, with their approval by the FDA occurring in 1999 and 1998 respectively. They are both neuraminidase inhibitors, acting on the same viral protein to prevent new virions from exiting infected cells. Both medications were found to be effective when administered within two days of symptom onset in a series of double-blind clinical trials carried out during the late '90s; these studies demonstrated similar efficacy in reducing flu symptoms duration and severity.

A systematic review carried out by Cochrane Collaboration in 2014 indicated that while Tamiflu can reduce symptoms duration slightly more effectively than Relenza due to its systemic action, it also seems to carry a greater risk for nausea, vomiting and psychiatric adverse events. Conversely, Relenza is generally better tolerated but its delivery via inhalation may not be suitable for everyone especially those with underlying respiratory conditions like asthma or chronic obstructive pulmonary disease.

Despite their differences, both zanamivir (Relenza) and oseltamivir (Tamiflu) are considered important tools for managing seasonal influenza outbreaks as well as potential pandemic situations. However, they should ideally complement rather than replace other preventive measures such as vaccination given that resistance could develop over time.

abstract image of a researcher studying a bottle of drug.

At what dose is Relenza typically prescribed?

Inhaled dosages of Relenza (zanamivir) for adults and children 7 years or older are two inhalations (10 mg) twice daily (20 mg/day total) for five days. Tamiflu (oseltamivir), in contrast, is taken orally with dosages typically at 75mg twice a day for five days in adults and adolescents who have been symptomatic for no more than 48 hours. Dosing adjustments may need to be made based on body weight for children under the age of 13, or those who may not weigh much. It's important that these medications are started as soon as flu symptoms appear or after exposure to the flu virus occurs.

At what dose is Tamiflu typically prescribed?

Tamiflu treatment for the flu typically starts with a dosage of 75 mg twice daily, taken orally for adults and children over 13 years old. For children between ages one to twelve, dosages are often weight-dependent; it's recommended that those weighing less than 15 kg take a dose of 30 mg twice daily, while those between 15-23 kg should have a dose of 45 mg twice daily. Dosage can be increased based on the patient's response and severity of symptoms. The course usually lasts five days but could be extended if necessary under doctor supervision. Remember, Tamiflu is most effective when started within two days from the onset of flu symptoms.

What are the most common side effects for Relenza?

Side effects that are commonly associated with Relenza and Tamiflu include:

  • Nausea
  • Vomiting
  • Diarrhea
  • Dizziness, headache
  • Sinusitis (inflammation of the sinus cavities in the head)
  • Bronchitis
  • Coughing
  • Ear, nose, or throat infections
  • Abdominal pain
  • Fatigue (general weakness)

These anti-viral medications for influenza may also cause serious side effects such as delirium and self-injury. If you experience any severe symptoms while taking these drugs, it's important to seek medical attention immediately.

abstract image of a patient experiencing side effect

Are there any potential serious side effects for Relenza?

Relenza and Tamiflu are both antiviral drugs used to treat influenza, but they can have different side effects. When using Relenza some people may experience:

  • Allergic reactions such as hives, difficulty breathing or swallowing, swelling of the face or throat
  • Bronchospasm (tightness in the chest, trouble breathing)
  • Skin rash or blisters

While taking Tamiflu, some individuals might encounter:

  • Severe skin reaction - fever, sore throat, swelling in your face or tongue, burning in your eyes
  • Behavior changes: confusion, hallucinations (hearing voices), unusual thoughts or behavior
  • Sudden dizziness and severe weakness
  • Stomach pain and vomiting

In case you observe any of these symptoms while taking either medication seek immediate medical attention.

What are the most common side effects for Tamiflu?

Common side effects of Tamiflu can include:

  • Nausea and vomiting (which usually occur in the first 2 days of taking the medication)
  • Headache
  • Fatigue, lack of energy
  • Cough or stuffy nose
  • Sleep problems (insomnia)
  • Mild rash or skin redness On rare occasions, some people may experience severe nausea, vomiting, or diarrhea. It's also worth noting that there have been reports of confusion and self-injury in patients with influenza who are taking Tamiflu, although these cases are extremely rare.

Are there any potential serious side effects for Tamiflu?

While Tamiflu is generally well-tolerated, certain side effects may arise. Here are some signs to watch out for:

  • Symptoms of an allergic reaction such as hives, difficulty breathing, swelling in your face or throat
  • Severe skin reactions: blisters or peeling rash, itching, redness
  • Behavioral changes: being more outgoing or aggressive than normal; confusion; agitation; panic attacks; hallucinations; paranoia; extreme fear
  • Sudden discomfort or illness: nausea and vomiting (severe); sudden dizziness or loss of consciousness
  • Unusual bleeding/bruising
  • Heart disturbances: chest pain with irregular heartbeats.

If you notice any of these symptoms after taking Tamiflu stop the medication immediately and call a healthcare professional right away. It's important to remember that while this list includes some potential side effects it does not mean everyone will experience them. Always discuss risks versus benefits with your healthcare provider before starting any new medication regimen.

Contraindications for Relenza and Tamiflu?

Both Relenza and Tamiflu, as with most antiviral medications, may cause side effects in some people. If you notice worsening of flu symptoms or an increase in unusual behavior (especially in children), please seek immediate medical attention.

Neither Relenza nor Tamiflu should be taken if you are allergic to oseltamivir phosphate (for Tamiflu) or zanamivir (for Relenza). Always inform your physician about any allergies or other medications you are taking; this includes herbal supplements and over-the-counter drugs.

Relenza is administered via inhalation, which might not be suitable for individuals with respiratory diseases such as asthma or chronic obstructive pulmonary disease due to the risk of bronchospasm. On the other hand, Tamiflu can be ingested orally making it a more appropriate choice for these patients.

Both these medicines should ideally be started within two days of flu symptom onset. However, they can also reduce complications even when initiated after this window period.

How much do Relenza and Tamiflu cost?

For the brand name versions of these drugs:

  • The price for a single dose pack (20mg) of Relenza averages around $66, which works out to about $33/day, as it is typically administered twice daily.
  • The price for 10 capsules of Tamiflu (75 mg) averages around $153, working out to approximately $30.60/day when taken twice daily or roughly half that at once-daily dosing.

So, if you are in the higher dosage range for Tamiflu (i.e., 150 mg/day), then brand-name Relenza could be less expensive on a per-day treatment basis. However, cost should not be your primary consideration in determining which of these influenza drugs is right for you.

As of now there are no generic versions available for either drug so costs remain significantly high compared with many other medications:

  • Relenza remains at its current pricing without an alternative option.
  • Oseltamivir (the active component in Tamiflu) does have a generic version available and may present some savings depending upon where purchased and insurance coverage. Prices can vary widely based on location and availability but do offer potential options given the lack of alternatives with these specific antiviral medications.

Popularity of Relenza and Tamiflu

Zanamivir, which is also known by the brand name Relenza, and oseltamivir, commonly referred to as Tamiflu, are both antiviral drugs prescribed for the treatment of influenza.

In 2020, it was estimated that around 2.5 million prescriptions were filled for Tamiflu in the US. This accounted for approximately 60% of all influenza antiviral prescriptions in the country. Oseltamivir's popularity has been relatively steady over recent years due to consistent annual outbreaks of influenza and its ease-of-use through oral administration.

On the other hand, Zanamivir or Relenza saw fewer than half a million prescriptions filled during that same period - accounting for just under 10% of all flu-related antiviral medication prescription fills. Its lower prevalence might be attributed to its mode of delivery; unlike Tamiflu which can be taken orally via pill form or liquid suspension, Zanamivir must be administered via inhalation using a special device (Diskhaler), making it less convenient for some patients.


Both Relenza (zanamivir) and Tamiflu (oseltamivir) are antiviral drugs that serve as integral components in the treatment of influenza A and B. They have been demonstrated to be effective through several clinical trials and research studies, showing greater efficacy than placebo treatments. Both medications work by inhibiting an enzyme called neuraminidase which is critical for the virus' replication process.

Relenza takes the form of a powder that is inhaled, whereas Tamiflu is taken orally. The route of administration chosen can depend on patient preference or specific circumstances such as difficulty swallowing pills.

Relenza may not be recommended for those with respiratory illnesses like asthma or chronic obstructive pulmonary disease due to its delivery mechanism, while Tamiflu has broader indications including prophylactic use in high-risk individuals exposed to flu.

Both drugs are available in generic forms, offering cost savings particularly for patients who must pay out-of-pocket. One might experience side effects from either drug; common ones include nausea and vomiting but these tend to be mild and transient.

It's crucial for patients to start taking these medications within 48 hours of symptom onset for optimal effectivity against the flu virus. Hence if you suspect flu infection it's important to seek medical help immediately.