Chemotherapy-Induced Nausea and Vomiting

Chemotherapy-induced nausea and vomiting (CINV) results from chemotherapy triggering enterochromaffin cells lining the GI tract to release serotonin, which activates 5-HT3 receptors and, via vagal afferents, the vomiting centre in the medulla oblongata; dopamine (D2) and neurokinin-1 (NK-1)/substance P pathways contribute alongside serotonin, with NK-1/substance P signalling playing the larger role once symptoms move into the delayed phase.^[1] CINV is not one problem but 5 distinct clinical patterns — acute, delayed, anticipatory, breakthrough, and refractory — each requiring a different management approach. The single most important management principle in this chapter is that prevention is far more effective than rescue: an antiemetic regimen matched to the emetogenic-risk tier of the chemotherapy regimen, given on a fixed schedule rather than PRN, and optimized starting with the very first cycle, is what keeps a patient able to tolerate a full course of curative or life-prolonging treatment.

• Patient-related: age under 50 years, female sex, low past alcohol intake, and a history of motion sickness or nausea/vomiting in pregnancy.
• Poor nausea/vomiting control in a previous chemotherapy cycle — the strongest predictor of anticipatory and refractory CINV in later cycles.
• High pre-treatment anxiety or expectation of nausea.
• The emetogenic potential, dose, and infusion rate of the specific chemotherapy agent(s) — slowing the infusion rate of some agents (e.g. cisplatin) can reduce emesis.
• Combination chemotherapy regimens — risk is driven by the single most emetogenic agent in the combination, not an average of its components.
• Multi-day chemotherapy regimens and high-dose chemotherapy (e.g. pre-stem-cell-transplant conditioning).
• Concurrent radiation therapy, particularly to the abdomen, pelvis, or craniospinal axis.
• Other nausea-provoking drugs taken concurrently — opioids, digoxin, and some antibiotics can cause or worsen nausea and vomiting independent of the chemotherapy itself.

History

• Onset, duration, and timing of nausea, retching, and vomiting relative to chemotherapy administration — this is what distinguishes acute from delayed from anticipatory CINV.
• Effect on the patient — oral intake, weight change, functional status (asthenia).
• A full description of the vomiting episodes and a complete medication history, since other drugs (opioids, digoxin, antibiotics) can cause or worsen nausea and vomiting independent of chemotherapy.

Physical examination

• Orthostatic vital signs to assess volume status.
• Abdominal examination for pain, distension, constipation, or signs of hemorrhage.
• Neurologic assessment, including cranial nerves, vestibular and pupillary function, and screening for extrapyramidal signs (relevant if the patient is already on a dopamine antagonist).

Investigations

• Electrolytes — urea, creatinine, sodium, potassium, and chloride to assess hydration status; calcium and albumin to screen for hypercalcemia as an alternative cause.
• Targeted drug-level screening (e.g. digoxin) if a specific drug is suspected as a contributing cause.

Medication is the most likely cause of nausea and vomiting in a patient receiving cancer treatment, but always consider and rule out other potential causes — fluid/electrolyte abnormalities, partial or complete bowel obstruction, brain or hepatic metastases, infection, and radiation therapy — rather than assuming every episode is CINV. Routine imaging or endoscopy is not indicated for straightforward acute or delayed CINV that responds to escalation of antiemetic therapy — reserve further workup for atypical features (see Red Flags).

Risk stratification: classify the regimen's emetogenic potential first

Antiemetic selection is driven entirely by the emetogenic potential of the chemotherapy regimen — classify every regimen before choosing a prophylactic antiemetic plan, and for a combination regimen, base the plan on the single most emetogenic agent in the combination, not an average of its components.^[4]

Table 1: Emetogenic Potential of Injectable Anti-Cancer Agents

Slowing the infusion rate of certain agents (e.g. cisplatin) may decrease emesis. Some agents (e.g. alemtuzumab, busulfan) appear in more than one tier because classification depends on the specific dose or schedule used.

Table 2: Emetogenic Potential of Oral Anti-Cancer Agents

Carboplatin is formally classified as moderately emetogenic, but a dose at an AUC of 5 or greater is treated as requiring triple therapy (adding an NK-1 receptor antagonist) under current risk-adapted moderately-emetogenic-chemotherapy recommendations — see Choose Initial Treatment. Some centres also manage higher-dose carboplatin regimens as fully highly emetogenic in practice; confirm the local institutional antiemetic protocol.^[5]

• Prevent or minimize acute, delayed, anticipatory, breakthrough, and refractory nausea and vomiting to maintain quality of life and support adherence to active cancer treatment.
• Achieve a complete response — no emesis and no rescue-medication use — in the current cycle and in every subsequent cycle, since inadequate control predicts worse control later unless the regimen is escalated.
• Avoid chemotherapy dose reductions or treatment delays caused by poorly controlled nausea and vomiting.
• Prevent complications of uncontrolled vomiting — esophageal tears, dehydration, anorexia, malnutrition, weight loss, pathological fracture from severe retching, metabolic alkalosis, and chloride/potassium depletion.

• Diet: small, light meals several times daily; avoid foods that are high in fat or have a heavy aroma; try dry, starchy foods such as crackers; if solid food cannot be tolerated, try ice chips and small sips of clear liquids; avoid food preparation, since the smell of food cooking often worsens nausea.
• Behavioural techniques: relaxation training to reduce physiologic arousal and anxiety; individualized exercise programs; systematic desensitization (a behavioural therapy that gradually conditions a relaxation response in place of the nausea response to chemotherapy-associated stimuli) specifically to prevent or reduce anticipatory nausea and vomiting.
• Other measures: keep movement to a minimum during active symptoms to avoid vestibular stimulation; acupuncture or acupressure at the P6 point; prioritize sleep, since sleeping through the highest-risk window reduces reported emesis.
• Administration route: use the oral route whenever the patient can tolerate it. Rectal antiemetics (e.g. prochlorperazine suppositories) are especially useful for outpatients who are vomiting or otherwise unable to take oral medication at home. For hospitalized patients who are actively vomiting, use the IV route.
• Scheduled, not PRN, dosing: give prophylactic antiemetics on a fixed schedule rather than in response to symptoms — regularly scheduled dosing is consistently more effective at preventing CINV than reactive dosing.

Pregnancy

Chemotherapy during pregnancy is uncommon and always managed by a specialist multidisciplinary team. When antiemetic therapy is needed, ondansetron is the best-studied and most commonly used agent. Dexamethasone can be used short-term but needs specialist input given fetal corticosteroid-exposure concerns. Data supporting NK-1 receptor antagonists and olanzapine in pregnancy are limited — avoid unless the treating specialist judges the benefit clearly outweighs the unknown risk. Avoid nabilone and other cannabinoids in pregnancy.

Breastfeeding

Ondansetron is considered compatible with breastfeeding. Data on the other antiemetics used for CINV in lactation are limited — involve the treating oncology team and a lactation-safety resource before continuing to breastfeed through a chemotherapy cycle.

Pediatrics

Pediatric antiemetic dosing for chemotherapy is weight-based and follows dedicated pediatric oncology protocols rather than the fixed adult doses in this chapter — consult the institutional pediatric oncology antiemetic protocol rather than extrapolating an adult mg dose.

Older adults

Reduce the maximum single IV ondansetron dose to 8 mg in patients age 75 or older because of dose-dependent QTc prolongation. Older adults are also more susceptible to olanzapine-related sedation and orthostatic hypotension — consider the 5 mg dose over the 10 mg dose when sedation risk is a concern.

Renal and hepatic impairment

5-HT3 receptor antagonists generally do not require dose adjustment in renal impairment. Use corticosteroids cautiously in patients with poorly controlled diabetes or active infection, given dexamethasone's metabolic and immunosuppressive effects. Use olanzapine and NK-1 receptor antagonists cautiously with closer monitoring in significant hepatic impairment given hepatic metabolism.

Track control as a "complete response" — no emesis and no rescue-medication use — separately for the acute (first 24 hours) and delayed (Days 2-5) phases of every cycle, and ask specifically about anticipatory symptoms starting from the second cycle onward. Check hydration status and electrolytes when vomiting has been significant. Reinforce that scheduled antiemetics must be taken on the fixed schedule given, not held in reserve for PRN use. Reassess the adequacy of the prophylactic regimen after every single cycle — inadequate control in one cycle predicts worse control in the next unless the regimen is escalated, making this the single highest-yield monitoring action a pharmacist can take in this condition.

1. Confirm the antiemetic regimen was actually given on schedule (not PRN) and matched to the true emetogenic-risk tier of the regimen — including using the single most emetogenic component of a combination regimen and applying the correct high-risk-MEC triple-therapy criteria (carboplatin at an AUC of 5 or greater, oxaliplatin-based regimens in women age 50 or younger, or select antibody-drug conjugates).
2. Rule out a non-chemotherapy cause — bowel obstruction, brain or hepatic metastases, electrolyte disturbance, infection, radiation therapy, or another emetogenic drug (opioids, digoxin, antibiotics) — before assuming the antiemetic regimen itself has failed.
3. For breakthrough symptoms, add a rescue agent from a pharmacologic class different from what was already used, dosed on a fixed schedule once started, and consider olanzapine 10 mg once daily for 3 days if it was not already part of the prophylactic regimen.
4. Escalate the prophylactic regimen for the next cycle rather than only treating the current episode — complete a full 4-drug regimen, switch to palonosetron, or add olanzapine if it is missing.
5. For anticipatory symptoms, add a benzodiazepine before the next cycle and refer for behavioural techniques (systematic desensitization).
6. For true refractory CINV despite a maximized 4-drug regimen, add nabilone; if nabilone fails, medical cannabis may be considered per Canadian family-physician guidance; refer to supportive/palliative oncology for ongoing uncontrolled symptoms.

• Dosing antiemetics PRN instead of on a fixed schedule for prophylaxis — scheduled dosing is consistently more effective.
• Selecting prophylaxis based on the least emetogenic drug in a combination regimen instead of its single most emetogenic component.
• Missing the high-risk-MEC triple-therapy triggers — carboplatin at an AUC of 5 or greater, oxaliplatin-based regimens in women age 50 or younger, and select antibody-drug conjugates — and under-treating these as standard double-therapy MEC.
• Continuing dexamethasone through Day 4 after an AC-based highly emetogenic regimen, when current evidence supports Day 1 only.
• Forgetting to reduce the dexamethasone dose by about half when co-administering an NK-1 receptor antagonist (aprepitant, fosaprepitant, or netupitant) — all 3 inhibit CYP3A4.
• Treating breakthrough symptoms by repeating or increasing the same drug class instead of switching to a genuinely different pharmacologic class.
• Missing anticipatory CINV as a preventable complication of inadequate first-cycle control, and responding to it with more acute antiemetic instead of a benzodiazepine plus behavioural referral.
• Relying on dimenhydrinate or scopolamine for CINV — effective for motion sickness, not for chemotherapy-induced nausea and vomiting.
• Missing a QTc-prolongation risk factor (electrolyte disturbance, other QTc-prolonging drugs, cardiac history) in a patient being started on ondansetron, granisetron, palonosetron, or haloperidol.
• Treating every episode of vomiting in a chemotherapy patient as CINV without considering bowel obstruction, metastatic disease, or another cause.

How to use this table: Doses are adult doses and require patient-specific confirmation, including renal/hepatic adjustment and the current institutional chemotherapy antiemetic protocol. Select any drug name to open its complete Pharmasist Drug Database page.

Serotonin 5-HT3 Receptor Antagonists

First-generation agents (ondansetron, granisetron) have equivalent efficacy and toxicity for acute-phase prevention; palonosetron is a second-generation agent with a substantially longer half-life.

Neurokinin-1 (NK-1) Receptor Antagonists

Not used as monotherapy. Aprepitant, fosaprepitant, and netupitant all inhibit CYP3A4 — reduce the co-administered dexamethasone dose by about half.

NK-1 Receptor Antagonist / 5-HT3 Receptor Antagonist Combination

Corticosteroids

Atypical Antipsychotic

Dopamine Antagonists

Both agents block dopaminergic receptors in the chemoreceptor trigger zone; the main practical limitation of this class is extrapyramidal side effects.

Benzodiazepines

Adjuncts only — never used as antiemetic monotherapy. Most useful for anticipatory CINV alongside behavioural techniques.^[3]

Cannabinoid

Reserved for refractory CINV or as an add-on given its side-effect burden and oral-only formulation. Medical cannabis (dried plant or oil extract) may be considered per Canadian family-physician guidance only in refractory CINV that has failed standard therapy and a trial of nabilone — it is not a routine antiemetic and is not recommended in standard antiemesis guidelines.