Nausea and vomiting during cancer treatment

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Treatment-related nausea is often more persistent and disabling than counted vomiting. Ask separately about nausea hours, retching, vomits, oral intake and rescue medicine. Acute symptoms occur during the first day and are strongly mediated by serotonin; delayed symptoms occur over subsequent days and involve substance P. Breakthrough symptoms occur despite prophylaxis, refractory symptoms recur in later cycles and anticipatory symptoms start before exposure after conditioning.

Prevention starts with the regimen rather than the patient’s first vomit. Classify the combined treatment, including dose and schedule, into high, moderate, low or minimal emetogenic risk and add individual susceptibility. High-risk regimens use several non-overlapping mechanisms before treatment and through the delayed period. Under-prescribing dexamethasone or later-day antiemetics, or failing to dispense them before the appointment, creates apparent drug failure that is actually delivery failure.

When symptoms break through, verify adherence and route, replace fluid and electrolytes and add a different antiemetic class. Repeating more ondansetron during marked constipation or QT risk may worsen the situation. Olanzapine is effective for breakthrough nausea but sedation matters. Metoclopramide can help non-obstructed upper-gut stasis but is unsuitable in complete obstruction and carries extrapyramidal risk. A benzodiazepine may reduce a conditioned anticipatory response but is not primary treatment for biochemical emesis.

Cancer treatment is not the only cause. Abdominal examination, bowel history, neurological review, medication reconciliation and calcium, sodium, renal and infection assessment are guided by the phenotype. A patient receiving immunotherapy with vomiting and hypotension may have cortisol deficiency; a patient with distension and obstipation may have obstruction. Changing the antiemetic without investigating these branches can turn a treatable emergency into a crisis.

Key points

Classify symptoms as acute within 24 hours, delayed after 24 hours, breakthrough despite prophylaxis, refractory in later cycles or anticipatory before treatment.
First-line prevention is chosen from the complete regimen’s emetogenic risk, not from the most familiar drug or the severity of symptoms after they begin.
Before every cycle, review what was prescribed, what was actually taken, timing, vomiting count, nausea burden, rescue use, constipation, sedation and cycle-specific control.
Highly emetogenic chemotherapy generally requires prophylaxis with an NK1 antagonist, a 5-HT3 antagonist, dexamethasone and olanzapine before treatment, followed by scheduled delayed cover.
Anthracycline–cyclophosphamide and high-risk carboplatin regimens need protocol-specific NK1-containing combination prevention; do not treat them as simple single-agent moderate risk.
Moderately emetogenic treatment commonly uses a 5-HT3 antagonist plus dexamethasone, with an NK1 antagonist or olanzapine added according to the exact regimen and individual risk.
Low-risk treatment usually needs one prophylactic drug and minimal-risk treatment no routine prophylaxis, while always providing a rescue plan.
Give prophylaxis before the anticancer exposure and write the delayed days explicitly; an as-required prescription started after vomiting is not adequate prevention.
Breakthrough emesis requires hydration assessment and a medicine from a different mechanism, such as olanzapine, dopamine antagonist or benzodiazepine for a selected anticipatory component.
Persistent vomiting makes oral rescue unreliable; change to intravenous, subcutaneous, buccal or rectal delivery where appropriate and reassess the diagnosis.
Ondansetron is effective but can cause constipation and QT prolongation; correct potassium and magnesium and review other QT-risk drugs.
Aprepitant inhibits CYP3A4 and requires a reduced dexamethasone dose in standard antiemetic protocols plus review of warfarin, contraception and other interactions.
Olanzapine improves nausea as well as vomiting but causes sedation, postural effects, glucose disturbance and anticholinergic burden; use a lower dose in frailty when protocol permits.
Anticipatory nausea is best prevented by excellent first-cycle control; behavioural desensitisation, relaxation and selected short-acting benzodiazepine support later cycles.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Emetogenic anticancer exposure

Cytotoxic drug, dose, route, combination and fractionated schedule determine intrinsic acute and delayed risk, while upper-abdominal or total-body radiotherapy adds site-dependent emesis.

Patient susceptibility

Younger age, female sex, little habitual alcohol, previous motion or pregnancy sickness, anxiety and poor control in an earlier cycle increase risk independently of regimen.

Conditioned anticipatory response

Smells, rooms and procedures can trigger nausea before later cycles after poorly controlled earlier vomiting, through learned autonomic and cortical associations.

Competing cancer and treatment causes

Bowel obstruction, brain disease, hypercalcaemia, uraemia, infection, opioid, constipation, gastritis and immune endocrine toxicity can coexist with chemotherapy timing.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Acute serotonin signalling
Enterochromaffin-cell serotonin activates vagal 5-HT3 pathways after cytotoxic injury, driving vomiting predominantly in the first 24 hours.
2
Delayed substance-P signalling
Neurokinin-1 receptor activation by substance P becomes prominent after the first day and explains benefit from NK1 antagonists in high-risk regimens.
3
Central pattern integration
Area postrema, nucleus tractus solitarius, vestibular, cortical and visceral inputs converge on brainstem motor networks coordinating nausea, retching and vomiting.
4
Conditioning recruits higher centres
Repeated pairing of treatment cues with emesis allows sight, smell and expectation to generate symptoms before a drug reaches the circulation.
5
Vomiting causes self-amplifying injury
Fluid, chloride, potassium and hydrogen loss produces alkalosis, renal impairment and delayed drug clearance, while poor intake worsens weakness and anticipatory fear.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Acute emesis

Nausea, retching or vomiting begins during treatment or within 24 hours, commonly reflecting serotonin-mediated vagal activation and inadequate immediate prophylaxis.

Delayed emesis

Symptoms peak beyond the first day after cisplatin, cyclophosphamide and other regimens and require scheduled later-day prevention, not acute rescue alone.

Breakthrough or refractory pattern

Symptoms despite correct prophylaxis in the current cycle are breakthrough; recurrence despite an improved plan in later cycles is refractory.

Anticipatory nausea

Symptoms triggered by travel, smell, clinic or cannulation before treatment indicate conditioning and need behavioural care plus stronger prevention.

Dehydration and electrolyte lossRed flag

Postural dizziness, tachycardia, dry mouth, oliguria, weakness or arrhythmia requires urgent renal, potassium and magnesium assessment and replacement.

Red flags requiring action

Fever, rigors, hypotension, confusion or new oxygen requirement after systemic anticancer treatment is neutropenic sepsis until treated immediately.
Colicky pain, abdominal distension, obstipation, faeculent vomiting or peritonism suggests malignant obstruction, ischaemia or perforation and needs urgent CT and surgical or acute-oncology review.
Progressive headache, focal deficit, seizure, papilloedema or falling consciousness can reflect brain metastasis, haemorrhage or raised intracranial pressure and needs emergency imaging.
Persistent vomiting with oliguria, postural hypotension, acute kidney injury, severe potassium or magnesium loss or QT prolongation requires monitored intravenous correction.
Haematemesis, coffee-ground vomit, melaena or falling haemoglobin requires an upper-gastrointestinal-bleeding pathway rather than routine chemotherapy antiemesis.
Severe headache, agitation, clonus, hyperreflexia and fever during serotonergic combinations raises serotonin toxicity and requires immediate medicine review.
Vomiting after immunotherapy may accompany adrenal crisis, hypophysitis, hepatitis, pancreatitis, colitis or neurological toxicity and needs organ-specific emergency assessment.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
First-line structured symptom and regimen reviewFirst stepFirst line
Why
Classify timing, severity, emetogenic risk, actual prophylaxis, adherence, rescue use, bowel pattern and individual susceptibility.
Interpretation and limitations
Use the exact treatment protocol and daily symptom record; nausea without vomiting still represents poor control and may require escalation next cycle.
02
Hydration, renal and electrolyte assessment
Why
Identify hypovolaemia, acute kidney injury, potassium, magnesium, sodium and acid–base disturbance caused by losses or another illness.
Interpretation and limitations
Use observations, weight, fluid balance and bloods; correct deficits before repeating QT-active antiemetics or nephrotoxic anticancer treatment.
03
FBC, infection and organ-toxicity tests
Why
Detect neutropenic sepsis, hepatic, pancreatic or immune endocrine disease when systemic illness accompanies vomiting.
Interpretation and limitations
Fever or deterioration after systemic treatment receives immediate sepsis care without waiting for neutropenia; select cortisol, glucose, liver or lipase from the syndrome.
04
ECG before or during QT-risk treatment
Why
Assess repolarisation when electrolyte loss, cardiac disease or several QT-prolonging antiemetics increase arrhythmia risk.
Interpretation and limitations
Correct potassium and magnesium and remove avoidable combinations; a previously normal ECG does not protect during new dehydration or medicine exposure.
05
CT abdomen and pelvis
Why
Identify malignant bowel obstruction, perforation, inflammation, ascites or other structural causes when pain, distension or obstipation occurs.
Interpretation and limitations
Do not use prokinetic metoclopramide across complete mechanical obstruction; imaging also guides drainage, stenting, surgery or symptom-focused care.
06
Brain imaging
Why
Detect metastasis, haemorrhage, oedema or hydrocephalus when headache, seizure, focal deficit or declining consciousness accompanies vomiting.
Interpretation and limitations
Use emergency CT for acute deterioration and contrast MRI for definitive intracranial mapping once stable; avoid lumbar puncture with mass effect.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Mechanical bowel obstruction

Colic, distension, reduced stool or flatus, altered bowel sounds and faeculent vomiting require CT and decompressive or palliative obstruction treatment.

Intracranial disease

Morning vomiting, headache, papilloedema, focal deficit or seizure suggests oedema, hydrocephalus, metastasis or haemorrhage requiring urgent brain imaging.

Metabolic and endocrine disturbance

Hypercalcaemia, hyponatraemia, uraemia, ketoacidosis, adrenal insufficiency and thyroid dysfunction cause nausea and cognitive or haemodynamic features beyond an antiemetic problem.

Infection or inflammation

Neutropenic sepsis, gastroenteritis, hepatitis, pancreatitis and immunotherapy-related organ inflammation may begin with vomiting and need immediate cause-directed tests.

Medicine and mucosal toxicity

Opioids, antibiotics, iron, NSAIDs, radiotherapy gastritis, mucositis and constipation can dominate symptoms even when the anticancer regimen has low emetogenicity.

Additional chapter-specific clues

Alternative-cause pattern

Fever, abdominal distension, obstipation, focal neurological signs, jaundice or hypotension points away from isolated treatment emesis and changes the pathway.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Before treatmentBuild prophylaxis from emetogenic riskFirst stepA systemic or radiation treatment course with potential emesis is prescribed.

1Classify the complete regimen and radiation field, then add age, sex, alcohol history, motion sickness, pregnancy sickness, anxiety and previous-cycle control.
2Prescribe the protocol combination before exposure with exact delayed-day doses, rescue from a different class and constipation, sedation and interaction counselling.
3Confirm dispensing and patient understanding before the first dose and arrange a 24-hour contact route and next-cycle review using an individual symptom record.

02Breakthrough symptomsChange mechanism and route while checking physiologyNausea or vomiting occurs despite the planned prophylaxis.

1Assess ABCDE stability, temperature, hydration, electrolytes, bowel and neurological signs, actual adherence and whether oral medicine remained absorbed.
2Replace fluid and electrolytes and give a rescue medicine from a different mechanism by a reliable route, avoiding duplicate toxicity such as QT prolongation or severe sedation.
3EscalationEscalate persistent symptoms to acute oncology for imaging or organ tests and rewrite the remaining delayed cover and next-cycle prophylaxis rather than merely renewing the failed regimen.

03Anticipatory symptomsBreak the conditioned cycleNausea begins before treatment in response to clinic, smell, travel or procedure cues.

1Confirm that current biological causes are controlled and reconstruct which previous cycle, cue and fear established the response.
2Optimise prophylaxis so no further post-treatment emesis reinforces conditioning and use relaxation, systematic desensitisation, psychological support and environmental modification.
3EscalationConsider a protocol short-acting benzodiazepine before the trigger when safe, reviewing driving, falls, respiratory and opioid co-exposure and avoiding indefinite escalation.

04Dangerous alternativeTreat the cause, not just the symptomAlternativeVomiting accompanies fever, peritonism, obstipation, neurological change, jaundice, hypotension or severe biochemical disturbance.

1Use ABCDE care and immediate sepsis, endocrine, obstruction, intracranial or bleeding pathway while withholding unsafe oral treatment and prokinetics when obstruction is possible.
2Obtain targeted bloods, ECG and CT or MRI without delaying antibiotics, corticosteroid for confirmed emergency indications, decompression or surgical and acute-oncology review.
3DefinitiveContinue parenteral symptom relief and hydration while definitive treatment and goals are agreed, then revise future antiemesis only after the competing cause is addressed.

Key medicines and prescribing safety3 treatments · regimens, roles and cautions

Blocks 5-HT3-mediated acute emesis and contributes to combination prophylaxis selected by treatment risk.

Ondansetron

For moderately emetogenic chemotherapy, a licensed oral schedule is 8 mg one to two hours before treatment, 8 mg twelve hours later, then 8 mg twice daily for up to five days; follow the regimen-specific protocol.

Moderate or severe hepatic impairment limits total daily dose to 8 mg; monitor QT and electrolyte risk, constipation or ileus and serotonergic combinations and avoid duplicating the same mechanism for breakthrough treatment.

Blocks NK1 signalling to prevent acute and particularly delayed nausea and vomiting from highly and selected moderately emetogenic chemotherapy.

Aprepitant

Give aprepitant 125 mg orally one hour before chemotherapy on day 1, then 80 mg once daily on days 2 and 3 as part of the licensed combination regimen.

CYP3A4 inhibition requires protocol dexamethasone reduction and interaction review; counsel about reduced hormonal-contraceptive efficacy and monitor warfarin, immunosuppressant and other narrow-therapeutic-index exposure.

Adds multi-receptor anti-nausea efficacy to 5-HT3, NK1 and corticosteroid prophylaxis and treats breakthrough symptoms through a different mechanism.

Olanzapine antiemetic use

Use 5 to 10 mg orally once daily on protocol days 1 to 4 for high-risk prophylaxis or selected breakthrough symptoms, with the lower dose often preferred in older or sedation-prone adults.

Monitor somnolence, postural hypotension, falls, glucose, anticholinergic burden and delirium; reconcile opioids and benzodiazepines and avoid driving when sedated.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Dehydration and kidney injury

Repeated losses and poor intake reduce renal perfusion, concentrate nephrotoxic drugs and may delay treatment or precipitate admission and organ failure.

Electrolyte and rhythm disturbance

Potassium and magnesium depletion increases weakness, ileus and ventricular arrhythmia risk, especially when several antiemetics prolong the QT interval.

Malnutrition and medicine failure

Persistent nausea reduces energy and protein intake and makes oral anticancer, antimicrobial, analgesic and endocrine medicines unreliable.

Aspiration and mucosal injury

Forceful or impaired-consciousness vomiting can cause aspiration pneumonitis, oesophageal tears, bleeding, dental damage and painful mucosal inflammation.

Anticipatory and treatment avoidance

Poor early control conditions future symptoms, heightens anxiety and can lead a patient to omit oral therapy or decline a potentially beneficial cycle.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Use a daily record of nausea duration, retching, vomits, intake, rescue dose, stool pattern and functional interference through the full acute and delayed risk window.
At each cycle verify that prophylaxis and delayed doses were dispensed and taken at the planned time; distinguish adherence failure from biological failure.
Monitor weight, orthostatic symptoms, urine output, renal function, potassium and magnesium when losses or reduced intake persist.
Review QT, constipation, extrapyramidal, sedative, glucose and steroid effects created by the antiemetic combination rather than attributing every symptom to chemotherapy.
Escalate any fever, focal neurological sign, abdominal distension, obstipation, bleeding, jaundice or haemodynamic change through the relevant emergency pathway.
Before the next cycle, upgrade prophylaxis after any breakthrough event and document the successful rescue class so the same inadequate plan is not repeated.
For anticipatory symptoms, track trigger intensity, procedural anxiety and response to behavioural intervention as well as post-treatment vomiting control.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Nausea is an endpoint

A patient can have no recorded vomit yet spend days unable to eat or function; prophylaxis should address both outcomes.

Delayed cover must leave with the patient

A perfect day-one infusion prescription fails when days two to four tablets were never dispensed, explained or tolerated.

Use a different rescue mechanism

Repeating the same saturated receptor class adds toxicity; breakthrough treatment usually gains more from a complementary pathway.

Constipation can masquerade as drug failure

Ondansetron and opioid combinations slow bowel function, creating nausea that worsens when further 5-HT3 antagonist is prescribed.

Anticipatory nausea is learned biology

It is neither fabricated nor best treated by reassurance alone; preventing initial emesis and desensitising cues targets its mechanism.

A low-risk regimen can coexist with a high-risk cause

Severe vomiting after minimally emetogenic treatment should increase suspicion for obstruction, infection, brain disease or metabolic toxicity.

11Common pitfallsFrequent interpretation and management errors.

01
Waiting for the first vomit before prescribing prophylaxis.
02
Classifying emetogenicity from one drug while ignoring the combined regimen, dose and schedule.
03
Omitting written delayed-day doses after excellent infusion-centre control.
04
Treating breakthrough symptoms by repeating only the same antiemetic mechanism.
05
Continuing oral rescue while repeated vomiting makes absorption unreliable.
06
Using metoclopramide despite complete mechanical obstruction or Parkinsonism.
07
Ignoring constipation and QT risk when combining ondansetron, opioid and electrolyte loss.
08
Missing adrenal insufficiency, neutropenic sepsis or immune toxicity during treatment.
09
Calling anticipatory nausea psychological in a dismissive way rather than treating conditioning.
10
Repeating an unsuccessful prophylaxis unchanged at the next cycle.