Oseltamivir comes as capsules or a syrup. You will need to take one capsule twice a day for five days to treat flu. Doctors prescribe lower doses for children, depending on how much they weigh. To prevent flu, you will need to take a capsule once a day for 10 days after exposure to the virus or for up to six weeks during an epidemic.
Zanamivir comes as an inhaler (puffer), similar to the type used to treat asthma. Each puff contains a small amount of the medicine. To treat flu (once you have symptoms), you need to use the puffer twice a day for five days. To prevent flu after you’ve been exposed to someone with the illness, you will need to use it once a day for 10 days. If there is a flu epidemic, you may be prescribed zanamivir for up to 28 days.
For oseltamivir and zanamivir to be effective, you need to start taking them within 48 hours of your symptoms first appearing. In children, zanamivir needs to be taken within 36 hours.
Special care
If you’re a woman and are pregnant or breastfeeding, your doctor may advise you to take either oseltamivir or zanamivir during a flu pandemic. Oseltamivir is the preferred medicine for women who are breastfeeding.
If you have advanced kidney disease, you may not be able to take oseltamivir. Always ask your GP for advice and read the patient information leaflet that comes with your medicine.
Side-effects of antiviral flu medicines
Zanamivir comes as an inhaler (puffer), similar to the type used to treat asthma. Each puff contains a small amount of the medicine. To treat flu (once you have symptoms), you need to use the puffer twice a day for five days. To prevent flu after you’ve been exposed to someone with the illness, you will need to use it once a day for 10 days. If there is a flu epidemic, you may be prescribed zanamivir for up to 28 days.
For oseltamivir and zanamivir to be effective, you need to start taking them within 48 hours of your symptoms first appearing. In children, zanamivir needs to be taken within 36 hours.
Special care
If you’re a woman and are pregnant or breastfeeding, your doctor may advise you to take either oseltamivir or zanamivir during a flu pandemic. Oseltamivir is the preferred medicine for women who are breastfeeding.
If you have advanced kidney disease, you may not be able to take oseltamivir. Always ask your GP for advice and read the patient information leaflet that comes with your medicine.
Side-effects of antiviral flu medicines
- feeling sick
- vomiting
- abdominal (tummy) pain
- diarrhoea
- headache
- conjunctivitis
These side-effects usually happen after you have taken the first dose of your medicine and will usually stop as you continue the course.
Side-effects of zanamivir are uncommon, but include:
- rashes
- difficulty breathing
- swelling of your face, mouth or throat
Because zanamivir can cause breathing difficulties, it isn't usually recommended if you have an underlying medical condition that affects your breathing system. Examples of such conditions include asthma or chronic obstructive pulmonary disease (COPD). Ask your GP for more advice.
