Medical Oncologist
Trastuzumab side effects
Fatigue, Chills and Flu-Like Symptoms — After a Trastuzumab Infusion
Flu-like symptoms after trastuzumab are common and usually not dangerous. They are most likely an infusion reaction — your body responding to the drug — and in most cases settle with rest. A small number of reactions do need urgent attention, and this page tells you which.
Medically reviewed by Dr. Bharati Devi Gorantla, Medical Oncologist, MBBS · MD · DM (Adyar, Chennai) · ECMO · MRCP SCE (UK) · Last reviewed August 2026
- Most common after your first dose — Infusion reactions happen most often during or shortly after the first trastuzumab infusion. Later doses are usually better tolerated.
- Usually settles with rest — Mild fever, chills, and fatigue from an infusion reaction typically ease within a day without specific treatment.
- Breathing changes are the warning sign — New shortness of breath, chest tightness, or wheezing after any trastuzumab dose needs same-day urgent assessment.
- Always tell your team — Even a mild reaction should be reported before your next cycle so the team can plan pre-medication or a slower infusion rate.
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Flu-like symptoms — fever, chills, and fatigue — are a well-recognised reaction to trastuzumab infusions, most common after your first dose. NCCN and ASCO guidance classifies mild reactions as expected and manageable with rest. Symptoms that worsen rapidly, cause breathing difficulty, or include chest pain need same-day emergency assessment.
How do you tell a normal infusion reaction from something more serious?
| Feature | Expected infusion reaction | Concerning — needs urgent review |
|---|---|---|
| Fever | Mild, settles with paracetamol and rest within a day | High, does not respond to paracetamol, or keeps returning |
| Chills and shivering | Come on during or just after the infusion and ease within hours | Severe rigors, or chills that worsen after the infusion has ended |
| Breathing | Unchanged, or very briefly uncomfortable and quickly settling | New shortness of breath, wheeze, or chest tightness at any point |
| Skin changes | Mild flushing or redness | Spreading hives, swelling of face or lips, or a rash with breathing difficulty |
| Response to pausing the infusion | Symptoms ease when the rate is reduced or the drip is stopped | Symptoms continue or worsen after the infusion has completely ended |
| Typically starts | During the first infusion or within a few hours after; much less likely with later doses | Can occur with any dose; severe reactions are rare but not impossible after early cycles |
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Not sure whether this counts as an emergency?
Call the helpline. It is always better to check than to wait.
Is this dangerous, and what can you do at home?
A mild infusion reaction — low-grade fever, chills, muscle aches, and tiredness — is not dangerous in itself. It is your body recognising an infused protein and reacting to it. For most people it eases within hours.
Rest and fluids are the most useful things you can do at home. Paracetamol in the dose your doctor has recommended can help with fever and aching. Do not take anti-inflammatory medicines such as ibuprofen without asking your oncology team first, as these can mask worsening that your team needs to see.
Report any reaction, even a mild one, before your next infusion. Your team may give you pre-medication — antihistamines or paracetamol before the drip starts — or slow the infusion rate, which reduces the chance of a reaction happening again.
Did you know?
Infusion-related reactions to trastuzumab are most common during the very first dose. NCCN guidance notes that the likelihood of a reaction falls significantly with each subsequent infusion, which is why oncology teams observe patients more closely during the first cycle.
Telling your team about any reaction — however mild — is the single thing that most reduces the risk of it happening again.
Source: NCCN Guidelines: HER2-Positive Breast Cancer, Management of Infusion-Related Reactions
Questions people ask after a trastuzumab infusion
Can I take paracetamol or ibuprofen for the fever and aching?
Paracetamol is generally safe to take in the dose your doctor has recommended, and it helps with the fever and muscle aches that come with a mild infusion reaction. Ibuprofen and other anti-inflammatory medicines are a different matter — they can interact with other medicines in your treatment plan or mask a worsening that your team needs to know about. Ask your oncology team before taking anything other than paracetamol. If they have already given you a list of medicines that are safe for you, follow that guidance.
The symptoms are mild. Do I still need to call my team?
Yes, and for two reasons. First, infusion reactions can worsen over a few hours rather than improve, and calling means your team knows to follow up. Second, even a mild reaction changes how they plan your next dose — pre-medication before the drip starts, or a slower infusion rate, can prevent a stronger reaction next time. A call today is much easier than managing a worse reaction at your next appointment. If symptoms are worsening rather than settling, do not wait at all.
I had no reaction to my first infusion. Does that mean I am safe from reactions now?
A trouble-free first infusion is a good sign, and reactions do become less likely with later doses for most people. However, a reaction can occur at any dose — including ones you have had without trouble before. The symptoms to stay alert to — particularly any new breathing difficulty, chest tightness, or a rash that spreads — apply at every infusion, not just the first. This is why your team still monitors you each time, even when your early doses went smoothly.
I am also taking an Ayurvedic or herbal supplement. Could it be causing this?
It is possible, and your oncology team needs to know about everything you are taking — prescription medicines, supplements, herbal preparations, and anything bought without a prescription. Some herbal products affect how the body processes cancer medicines, or can cause reactions that look like infusion side effects. There is no judgement in telling your team what you are taking — they need the full picture to care for you safely. Please mention it at your next appointment, or call and tell them now if your symptoms are anything other than very mild.
Will an infusion reaction mean trastuzumab has to be stopped permanently?
A mild infusion reaction does not usually lead to trastuzumab being stopped. Most people continue treatment after pre-medication and a slower infusion rate are introduced, and many complete their full course without further reactions. A severe reaction — particularly one involving breathing difficulty or a significant drop in blood pressure — may lead your oncologist to pause treatment while it is assessed and managed. The decision is made based on the severity of the reaction and how you respond to treatment for it, weighing both against how important trastuzumab is to your overall plan.
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Common questions
Frequently asked questions
How long do flu-like symptoms after trastuzumab usually last?
For most people, mild fever, chills, and fatigue from an infusion reaction ease within a few hours to a day. If symptoms are still present and not improving after 24 hours, or if they worsen at any point, call your oncology team the same day rather than waiting for your next appointment. Symptoms that persist beyond a day are worth reporting even when they feel mild, because your team may want to rule out something other than a straightforward infusion reaction.
Is trastuzumab harder on the body than chemotherapy?
Trastuzumab targets a specific protein on cancer cells rather than broadly affecting dividing cells, so its side effect profile is different from chemotherapy. Infusion reactions and the flu-like symptoms that sometimes follow are among the most common effects. Chemotherapy-typical effects such as significant hair loss or severe nausea are not usually caused by trastuzumab alone. That said, trastuzumab requires monitoring of heart function over time, which is why your team arranges regular heart scans throughout treatment — something worth asking your oncologist to explain at your next visit.
Can the reaction be worse the second time than the first?
Reactions more commonly ease with later doses rather than worsen, and once a reaction has occurred, most oncology teams introduce pre-medication before the next infusion and run the drip more slowly. However, a reaction at a later dose is possible, which is why monitoring continues at every cycle. Reporting your first reaction promptly is exactly what allows your team to take steps that reduce the risk of a stronger one next time. Do not wait until your next scheduled appointment to mention it.
What is the difference between an infusion reaction and an allergic reaction?
An infusion reaction is a broad term for any symptom that occurs during or shortly after the drip. Most are not true allergic reactions — they are the immune system responding to an infused protein in a way that causes temporary inflammation. A true severe allergic reaction, or anaphylaxis, involves the immune system responding in a way that can rapidly affect breathing and blood pressure. Swelling of the face or throat, severe breathing difficulty, and a spreading rash together are signs of anaphylaxis rather than a routine reaction — go to emergency care immediately for those signs.
Is there anything specific to avoid at home on the day of the infusion?
Rest and staying well hydrated are the most useful things on the day of the infusion and the day after. Avoid strenuous physical activity until the flu-like symptoms have settled. There are no foods that specifically interact with trastuzumab, but your team may have specific guidance based on what other medicines you are taking alongside it. If you are also receiving chemotherapy, your team will give you separate guidance for those medicines, which have their own considerations that are distinct from trastuzumab.