Medical Oncologist
Rituximab side effects
Rituximab Infusion Reactions: — Why the First Infusion Is Different
A reaction during or after a rituximab infusion is not the same as a drug allergy. It is your immune system responding to the treatment, and your infusion team is prepared for it. Knowing what is expected helps you recognise the few signs that need urgent attention.
Medically reviewed by Dr. T. Raghavender Reddy, Medical Oncologist, MBBS · DM (Medical Oncology) · MD (Radiation Oncology) · Last reviewed August 2026
- The first infusion carries the highest risk — Reactions are most common during or within a few hours of the first dose. Later infusions are usually better tolerated.
- Your team prepares for this — Pre-medication — paracetamol and an antihistamine — is given before every rituximab infusion as standard care.
- Most reactions are mild — Chills, fever, and flushing during the infusion are common and managed by slowing the drip.
- A few signs need emergency care — Difficulty breathing, throat tightening, or sudden collapse after leaving the clinic means go to emergency now.
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Infusion reactions are expected with rituximab, especially on the first dose. Most are mild — chills, fever, flushing — managed by your team slowing the drip. The signs that need emergency care are difficulty breathing, throat tightening, or sudden collapse. If any occur after you leave the clinic, go to emergency — do not wait for a callback.
Why does a reaction happen at all?
Rituximab attaches to a protein called CD20 on the surface of B cells. When it triggers cell death, your immune system releases signalling chemicals — cytokines — that can cause fever, chills, flushing and other symptoms.
This is called a cytokine release reaction. It is not the same as a drug allergy, and it does not mean the drug is harming you or failing to work.
The infusion team manages these reactions by slowing or briefly stopping the drip. Once symptoms settle, the infusion is usually restarted at a slower rate, and most people complete their first dose.
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Which symptoms are expected and which need urgent review?
| Symptom | Expected — managed by your team during infusion | Needs urgent review after leaving clinic |
|---|---|---|
| Chills or shivering | Very common, especially early in the infusion | Severe or ongoing once you are home |
| Fever | Mild fever during infusion — managed with paracetamol | Fever that rises or persists several hours after leaving |
| Flushing or skin redness | Common — settles as infusion slows | Spreading hives, especially with any breathing difficulty |
| Headache or nausea | Common mild side effects | Severe, sudden, or with confusion or vision changes |
| Difficulty breathing | Not expected at any point | Emergency — go now, do not call first |
| Swelling of face or throat | Not expected at any point | Emergency — go now, do not call first |
| Typically starts | During infusion or in the first few hours after the first dose | Rarely, several hours after leaving — watch throughout infusion day |
What should you do at home after your first rituximab infusion?
- Do not return home alone — stay with someone for several hours after your first infusion.
- Do not drive yourself home if you experienced any reaction during the infusion.
- Keep the clinic emergency contact number with you for the rest of the day.
- Note the time the infusion ended so you can tell emergency staff if you need to go to hospital later.
- If you develop mild chills, low-grade fever or flushing, rest and take paracetamol as your team has advised, and monitor whether symptoms settle.
- If symptoms worsen rather than settle, or any red flag appears, go to emergency — do not call the clinic and wait for a callback.
Did you know?
Reactions to rituximab are most common with the first infusion. NCCN and ESMO guidance notes that subsequent infusions are typically better tolerated, and many patients who had a mild first reaction complete their full course without further incidents.
Pre-medication before each infusion — not just the first — is standard precisely because this risk does not disappear entirely.
Source: NCCN Guidelines for B-Cell Lymphomas; ESMO Clinical Practice Guidelines
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Common questions
Frequently asked questions
Is a reaction to rituximab the same as a drug allergy?
No, and the distinction matters for your treatment. Most rituximab reactions are cytokine release reactions — your immune system responding to the rapid breakdown of B cells — rather than a true drug allergy. A true allergic reaction is much rarer. The difference is important because a cytokine release reaction usually means the infusion is slowed or paused and restarted, whereas a confirmed allergy may mean the drug cannot be used again. Your team will document which type of reaction you had.
Will I have a reaction every time I receive rituximab?
Not necessarily. Reactions are most likely during the first infusion, and NCCN guidance notes that subsequent infusions are generally better tolerated. Pre-medication is given before each dose, and the infusion rate can be adjusted based on how you responded previously. If you had a mild reaction first time, your team will plan accordingly for the next dose. Many people who react on the first infusion go on to complete their full course without further problems.
How long after the infusion can a reaction still happen?
Most reactions occur during the infusion or in the first few hours after it ends. This is why your team monitors you before discharge, and why staying with someone on infusion day is advised. Delayed reactions beyond that window are uncommon but possible. If new symptoms develop the following day, contact your oncology team to discuss whether they are likely to be related to the infusion.
Can I take antihistamines at home if I get hives after leaving the clinic?
Call your team first. If hives are mild and settling, your team may advise an antihistamine that is safe alongside your other medications. If hives are spreading rapidly or you have any breathing difficulty, that is not a situation for a tablet — go to emergency immediately. An antihistamine does not treat anaphylaxis, and taking one at home can delay care you may urgently need.
What does the infusion team do when a reaction happens during the drip?
The infusion is slowed or stopped, and you may be given additional medication — which can include a steroid, a stronger antihistamine, or other support — depending on how severe your symptoms are. Once they settle, the infusion is usually restarted at a slower rate. Your infusion suite has the equipment and medication to manage reactions, which is why rituximab is always given in a supervised clinical setting. You will not be sent home while actively reacting.