Trastuzumab may cause side effects, although many of these will become less severe over time. Trastuzumab may also be used alongside chemotherapy medicines which can cause other types of side effects.
Common side effects
These common side effects of trastuzumab happen in up to 1 in 10 people. There are things you can do to help cope with them:
Feeling tired and difficulty sleeping (insomnia)
Avoid caffeine, alcohol, heavy meals and exercise for a few hours before going to bed. Relax before bedtime by taking a warm bath or listening to calming music.
Do not drive, ride a bike, or use tools or machinery if you're feeling tired.
Diarrhoea or vomiting
Drink plenty of fluids, such as water or squash, to avoid dehydration. Signs of dehydration include peeing less than usual or having dark strong-smelling pee.
If you take the combined pill or progestogen-only pill and you're being sick (vomiting), or have had diarrhoea for more than 24 hours, your contraception may not protect you from pregnancy. Check the pill packet for advice.
Constipation
Try to get more fibre into your diet such as fresh fruit and vegetables and cereals. Drinking plenty of water each day can also help. If you can, try to exercise more regularly, for example, by going for a daily walk.
It's safe to use a laxative if your constipation does not go away. Check with a pharmacist or doctor which laxative would be best for you.
Loss of appetite and weight loss
You may lose your appetite while on trastuzumab as it can affect your taste or make you feel sick. This may cause you to lose weight.
Try to choose foods you normally enjoy but avoid rich or spicy food. Try eating smaller meals but more often. Talk to your doctor if your symptoms do not improve or get worse.
Pain in your muscles, joints or stomach
Using a heat pad or covered hot water bottle may help. Speak to a pharmacist about painkillers for mild to moderate pain. Talk to your doctor if the pain does not go away or is severe.
A runny nose
Tell your doctor or nurse who may recommend an antihistamine for you to take.
Sore, red eyes (conjunctivitis) or watery eyes
Tell your doctor or nurse as you may need treatment.
Shaking (tremors)
Speak to your doctor.
Feeling dizzy
If trastuzumab makes you feel dizzy when you stand up, try getting up very slowly or stay sitting down until you feel better. If you begin to feel dizzy, lie down so you do not faint, then sit until you feel better.
Do not drive, ride a bike, or use tools or machinery if you feel dizzy.
Hair loss
Your hair may thin but you're unlikely to lose all your hair. It can start after your first or second cycle of treatment and is usually temporary. Your hair will grow back after you finish your treatment.
Speak to your doctor if the advice on how to cope does not help and a side effect is bothering you or does not go away.
Serious side effects
Call a doctor or call 111 straight away if:
- you have symptoms of an infection such as a high temperature, feeling shivery or you feel unwell even though your temperature is normal – trastuzumab can reduce the number of white blood cells in your blood which increases your risk of severe infections
- you have swollen feet or ankles, or stomach or lower back pain – these can be signs of heart problems
Immediate action required: Call 999 or go to A&E now if:
- you have chest pain – this could be a sign of heart problems
- you have difficulty breathing
Do not drive to A&E. Ask someone to drive you or call 999 and ask for an ambulance.
Bring all the medicines you take with you.
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction to trastuzumab (anaphylaxis).
Immediate action required: Call 999 now if:
- your lips, mouth, throat or tongue suddenly become swollen
- you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
- your throat feels tight or you're struggling to swallow
- your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
- you suddenly become very confused, drowsy or dizzy
- someone faints and cannot be woken up
- a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)
You or the person who's unwell may also have a rash that's swollen, raised, itchy, blistered or peeling.
These can be signs of a serious allergic reaction and may need immediate treatment in hospital.
Do not drive yourself to A&E.
The person you speak to at 999 will give you advice about what to do.
Other side effects
These are not all the side effects of trastuzumab. For a full list, see the leaflet inside your medicine packet.
Reporting side effects
You can report any suspected side effect using the Yellow Card safety scheme.
Visit the Yellow Card website for more information about reporting side effects.