Anti-infective
Influenza antivirals
Oseltamivir and related drugs — Reduce the duration of flu and protect high-risk people — most useful started early.
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
What it is
These antivirals treat and sometimes prevent influenza ("the flu"). They are mainly used for people at higher risk of complications and when flu is known to be circulating.
How it works
They block an enzyme (neuraminidase) the influenza virus needs to spread from cell to cell, limiting how far the infection gets — which is why starting early, before the virus has multiplied, matters most.
In practice
In practice the benefit is modest and time-critical: these antivirals shorten flu by roughly a day and may reduce complications in those at risk, but only if started within about 48 hours of symptoms, so they are used selectively — chiefly for at-risk patients and during recognised influenza circulation, often guided by national alerts rather than given to everyone with a cough. The dose is reduced in renal impairment, nausea is the common side-effect, and they complement rather than replace vaccination, which remains the main preventive measure.
Examples
Practical use
How to take it & use it well
- Take oseltamivir as soon as possible after flu symptoms start, ideally within the first day or two, as antivirals work best when started early.
- Take it with food to reduce the chance of nausea.
- Complete the full course as prescribed, even if you start to feel better, to give the best chance of benefit.
- Space your doses evenly and keep well hydrated and rested while you recover.
- Tell your clinician if you have reduced kidney function, as the dose may need adjusting.
- Seek urgent advice if breathing becomes difficult, symptoms suddenly worsen, or you do not improve as expected.
Common uses
- Treatment of influenza in at-risk patients
- Post-exposure prevention in some high-risk situations
- Outbreak control (e.g. care homes)
Monitoring
- Symptom course and any complications
- Renal function for dosing
- Tolerability (nausea)
Weighing it up
Advantages & disadvantages
Advantages
- Started early, it can shorten the duration of flu symptoms.
- It may reduce the risk of complications in people who are more vulnerable.
- It can be used to help prevent flu after close contact in certain situations.
- It is taken as a convenient oral medicine.
Disadvantages
- It works much less well if started more than a day or two after symptoms begin.
- Nausea and vomiting are common, especially without food.
- The dose needs adjusting in people with reduced kidney function.
- It is not a substitute for the flu vaccine and does not give lasting protection.
Key safety principles
What to watch for
- Most effective started within about 48 hours of symptoms; benefit is modest.
- Reduce the dose in renal impairment (oseltamivir).
- Nausea and vomiting are common; they complement but do not replace vaccination.
Key interactions
What to avoid or check alongside
- Oseltamivir has relatively few significant medicine interactions compared with many antivirals.
- Live attenuated flu vaccines, such as the nasal spray, may be less effective if given close to the antiviral.
- Reduced kidney function affects how the medicine is cleared, so dosing is adjusted accordingly rather than because of another drug.
- Other medicines that cause nausea can add to the stomach upset some people feel.
- Always tell your pharmacist about all your medicines, as advice can change with your overall health and kidney function.
Patient & carer advice
- Start as soon as possible after symptoms begin
- Take with food to reduce nausea
- The yearly flu vaccine is still the best protection
Use with
Related clinical calculators
Dose and risk decisions for this class often depend on renal function, weight or bleeding/stroke risk. These tools help:
Answers
Influenza antivirals: frequently asked questions
Why must I start oseltamivir quickly?
Antivirals for flu work by slowing the virus's spread in the body, which is most active early in the illness. Starting within the first day or two gives the best chance of shortening symptoms; started later, the benefit is much smaller.
Does oseltamivir replace the flu vaccine?
No. The flu vaccine helps prevent flu and gives lasting seasonal protection, while oseltamivir treats or, in some cases, helps prevent flu after a specific exposure. The vaccine remains the main way to protect against flu.
Why does it sometimes make people feel sick?
Nausea and vomiting are the most common side effects of oseltamivir, particularly when taken on an empty stomach. Taking it with food can help reduce this. Tell your clinician if vomiting is severe or you cannot keep doses down.
Do I need a dose change if my kidneys are not working well?
Possibly. Oseltamivir is cleared by the kidneys, so people with reduced kidney function may need an adjusted dose. Tell your clinician about any kidney problems so your treatment can be set correctly.
Can oseltamivir be used to prevent flu?
In certain situations, such as after close contact with someone who has flu, oseltamivir may be used to help prevent infection in people at higher risk. This is decided by a clinician based on the individual circumstances.
Authoritative sources
Always verify against the source
This overview is for orientation. For doses, interactions, contra-indications and the full monograph, use:
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