Chemotherapy-Induced Nausea and Vomiting

Clinical Snapshot

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.

Recognize the Condition

The 5 clinical patterns of CINV

Correct identification of which pattern is occurring changes the management approach entirely.

Acute CINV

Starts within minutes to hours after chemotherapy administration and typically resolves within 24 hours. Serotonin (5-HT3) is the dominant neurotransmitter: chemotherapy and radiation cause enterochromaffin cells lining the GI tract to release serotonin, activating 5-HT3 receptors that stimulate the vomiting centre in the medulla oblongata, with dopamine (D2) and NK-1 receptors also contributing. Patient-related risk factors include younger age, low past alcohol intake, poor symptom control in a prior cycle, a history of motion sickness or nausea in pregnancy, and female sex.^[2]

Delayed CINV

Begins at least 24 hours after chemotherapy and can last 6-7 days. Serotonin is less important in this phase — substance P/NK-1 signalling plays the dominant role, which is why NK-1 receptor antagonists and multi-day dexamethasone specifically target delayed rather than acute symptoms. Cisplatin and cyclophosphamide are classic causes of both acute and delayed emesis, often with a symptom-free interval in between.

Anticipatory CINV

A conditioned (learned) response to previously poorly-controlled nausea and vomiting, occurring before, during, or immediately after chemotherapy administration — before acute symptoms would be physiologically expected. It typically worsens with each subsequent cycle and, left unaddressed, can lead a patient to refuse further chemotherapy. The single best way to prevent it is excellent acute and delayed symptom control starting with the very first cycle — anticipatory CINV is essentially a preventable complication of inadequate earlier-cycle prophylaxis, not primarily a psychological problem to be treated in isolation.^[3]

Breakthrough CINV

Nausea or vomiting occurring within 5 days of treatment despite an optimized, guideline-concordant prophylactic antiemetic regimen. It requires rescue therapy with an antiemetic from a pharmacologic class different from what was already used for prophylaxis, and should prompt reassessment of the prophylactic regimen for the next cycle rather than being treated as an isolated event.

Refractory CINV

Nausea or vomiting occurring in a chemotherapy cycle after antiemetic prophylaxis has already failed to control symptoms in an earlier cycle. This pattern demands escalation of the prophylactic regimen for subsequent cycles — repeating the same regimen that already failed is not appropriate.

Risk Factors

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.

Red Flags & Refer

Most CINV is managed with scheduled prophylactic and rescue antiemetics in the outpatient setting, but escalate promptly for any of the following:

Signs of severe dehydration or electrolyte derangement from refractory vomiting — marked orthostatic hypotension, confusion, minimal urine output, or profound weakness — needs urgent assessment for IV fluid and electrolyte replacement, not another oral antiemetic trial.
Inability to tolerate any oral intake, including oral antiemetics — switch immediately to a rectal, subcutaneous, or IV route rather than continuing to prescribe oral therapy the patient cannot keep down.
QTc-prolongation risk — a patient started on ondansetron, granisetron, palonosetron, or haloperidol who also has hypokalemia, hypomagnesemia, a personal or family history of long QT syndrome, other QTc-prolonging drugs, or significant bradycardia needs ECG monitoring or an antiemetic-class switch before continuing.
Hematemesis, severe or worsening abdominal pain, or abdominal distension — evaluate urgently for a Mallory-Weiss tear, bowel obstruction, or another surgical cause rather than assuming ongoing CINV.
New neurologic signs (headache, altered mental status, focal deficits) — evaluate for brain metastases or another CNS cause rather than attributing vomiting to chemotherapy alone.
Vomiting that persists or worsens despite a correctly-dosed, guideline-concordant regimen given on schedule — reassess the diagnosis and regimen with the oncology team rather than repeatedly escalating the same drug class.^[4]

Assessment & Diagnosis

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

Emetogenic risk	Representative agents
High (over 90%)	Anthracycline/cyclophosphamide (AC) combinations, carmustine, cisplatin, cyclophosphamide (over 1500 mg/m²), dacarbazine, sacituzumab govitecan, streptozocin, trastuzumab deruxtecan
Moderate (30-90%)	Alemtuzumab, azacitidine, bendamustine, busulfan, carboplatin, cyclophosphamide (under 1500 mg/m²), cytarabine (over 1000 mg/m²), cytarabine/daunorubicin liposome, daunorubicin, dinutuximab, doxorubicin, epirubicin, idarubicin, ifosfamide, irinotecan, methotrexate (dose-dependent), oxaliplatin, temozolomide, trastuzumab deruxtecan
Low (10-30%)	Abemaciclib, alpelisib, amivantamab, axicabtagene ciloleucel, brentuximab vedotin, brexucabtagene autoleucel, cabazitaxel, carfilzomib, ciltacabtagene autoleucel, cytarabine (under 1000 mg/m²), docetaxel, doxorubicin liposomal, enfortumab vedotin, eribulin, etoposide, 5-fluorouracil, gemcitabine, gemtuzumab ozogamicin, idecabtagene vicleucel, isatuximab, L-asparaginase, lisocabtagene maraleucel, melphalan, mitomycin, mitoxantrone, mogamulizumab, paclitaxel, pemetrexed, polatuzumab vedotin, pralatrexate, raltitrexed, regorafenib, tebentafusp, thiotepa, tisagenlecleucel, topotecan, trastuzumab emtansine, tremelimumab
Minimal (under 10%)	Alemtuzumab, atezolizumab, avelumab, bevacizumab, bleomycin, bortezomib, busulfan, cemiplimab, cetuximab, cladribine, daratumumab, decitabine, dexrazoxane, dostarlimab, durvalumab, epcoritamab, fludarabine, glofitamab, ipilimumab, nivolumab, obinutuzumab, panitumumab, pembrolizumab, pertuzumab, ramucirumab, rituximab, siltuximab, trastuzumab, vinblastine, vincristine, vindesine, vinorelbine

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

Emetogenic risk	Representative agents
High (over 90%)	Procarbazine
Moderate (30-90%)	Azacitidine, binimetinib, bosutinib, cabozantinib, ceritinib, crizotinib, cyclophosphamide, dabrafenib, encorafenib, etoposide, fedratinib, imatinib, lenvatinib, lomustine, midostaurin, mitotane, niraparib, olaparib, selinexor, temozolomide
Low (10-30%)	Acalabrutinib, afatinib, alectinib, axitinib, bosutinib, brigatinib, capecitabine, dasatinib, everolimus, etoposide, fludarabine, ibrutinib, idelalisib, lapatinib, larotrectinib, lenalidomide, lorlatinib, mercaptopurine, nilotinib, osimertinib, palbociclib, pazopanib, ponatinib, regorafenib, ribociclib, selpercatinib, sonidegib, sunitinib, tegafur-uracil, tepotinib, thalidomide, trametinib, tucatinib, vandetanib, venetoclax, vorinostat, zanubrutinib
Minimal (under 10%)	Asciminib, belzutifan, busulfan, chlorambucil, erlotinib, gefitinib, hydroxyurea, L-phenylalanine mustard, melphalan, methotrexate, pomalidomide, ruxolitinib, 6-thioguanine, sorafenib, vemurafenib, vismodegib

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]

Treatment Targets

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.

Choose Initial Treatment

Direct treatment rule

Match prophylaxis to emetogenic-risk tier

Classify the regimen (by its single most emetogenic component) into one of the 4 tiers below, then give the corresponding prophylactic regimen before chemotherapy starts and on a fixed schedule through the risk period — never PRN for prophylaxis.^[2]

Prophylactic regimen by emetogenic-risk tier

High emetogenic risk (over 90%) — e.g. cisplatin, cyclophosphamide over 1500 mg/m², anthracycline/cyclophosphamide combinations

Day 1, before chemotherapy: a 5-HT3 receptor antagonist (e.g. ondansetron 16-24 mg PO) + an NK-1 receptor antagonist (aprepitant 125 mg PO, fosaprepitant 150 mg IV, or netupitant/palonosetron 300 mg/0.5 mg PO as a combined single dose) + dexamethasone 12 mg PO/IV (reduce to 8-12 mg when combined with an NK-1 receptor antagonist, since aprepitant, fosaprepitant, and netupitant all inhibit CYP3A4) + olanzapine 10 mg PO (5 mg if sedation is a concern).^[2]

Anthracycline/cyclophosphamide (AC) regimens: continue only olanzapine 10 mg (or 5 mg) once daily on Days 2-4 — dexamethasone is not needed beyond Day 1.

Non-AC highly emetogenic regimens (e.g. cisplatin): continue dexamethasone 8 mg once daily on Days 2-3 and olanzapine 10 mg (or 5 mg) once daily through Day 4; continue the NK-1 receptor antagonist per its own labelled course (aprepitant 80 mg once daily Days 2-3; a single dose of fosaprepitant or netupitant/palonosetron already covers the full course).

Moderate emetogenic risk (30-90%) — e.g. carboplatin, oxaliplatin, most anthracyclines outside an AC combination, irinotecan

Standard-risk MEC a 5-HT3 receptor antagonist + dexamethasone 8-12 mg PO/IV on Day 1; continue dexamethasone 8 mg once daily on Days 2-3 for delayed-phase coverage, or substitute olanzapine on Days 2-4 as a dexamethasone-sparing option.

High-risk MEC — add an NK-1 receptor antagonist (triple therapy) for carboplatin at an AUC of 5 or greater, oxaliplatin-based regimens in women age 50 or younger, and select antibody-drug conjugates including sacituzumab govitecan and trastuzumab deruxtecan.^[5]

Low emetogenic risk (10-30%)

A single agent on Day 1 only — dexamethasone 8 mg PO/IV, a 5-HT3 receptor antagonist, or a low-dose dopamine antagonist (e.g. metoclopramide) — is sufficient for acute prevention. Routine delayed-phase (multi-day) prophylaxis is not needed.^[6]

Minimal emetogenic risk (under 10%)

No routine prophylactic antiemetic is recommended. Treat symptomatically with a PRN agent (e.g. metoclopramide or prochlorperazine) only if nausea or vomiting actually occurs.

Multi-day and high-dose chemotherapy

Multi-day regimens (e.g. multi-day cisplatin): give antiemetics on each day chemotherapy is given — a 5-HT3 receptor antagonist once daily + dexamethasone + aprepitant + olanzapine 5 mg once daily is the preferred combination; for highly emetogenic multi-day regimens, dexamethasone and olanzapine may be continued for up to 2 days after the last chemotherapy dose, and for moderately emetogenic multi-day regimens, olanzapine alone may be continued for up to 2 days after the last dose.^[7]

High-dose chemotherapy (e.g. pre-stem-cell-transplant conditioning): use a 5-HT3 receptor antagonist + dexamethasone + an NK-1 receptor antagonist; olanzapine can be added to this regimen as well.

Managing each phase of CINV

Acute and delayed CINV are prevented, not rescued — use the risk-tier-matched regimen above exactly as scheduled; do not wait for symptoms to appear before dosing.

Breakthrough CINV (occurring despite an adequate prophylactic regimen): give a rescue agent from a pharmacologic class different from what was already used for prophylaxis, dosed on a fixed schedule rather than PRN once started. Preferred olanzapine 10 mg PO once daily for 3 days if olanzapine was not already part of the prophylactic regimen; alternatives include adding a dopamine antagonist (metoclopramide or prochlorperazine) or a different-class 5-HT3 receptor antagonist. Reassess and escalate the prophylactic regimen itself for the next cycle — breakthrough symptoms mean the current prophylaxis was inadequate, not just that this one episode needs treating.^[7]^[8]

Anticipatory CINV: prevent it by optimizing acute/delayed control starting with the first cycle. Once established, add a benzodiazepine — Alternative lorazepam 0.5-2 mg PO/SL starting the night before or the morning of the next chemotherapy cycle — alongside behavioural techniques (systematic desensitization, relaxation training), and escalate the antiemetic prophylaxis regimen for the next cycle rather than treating the anticipatory symptom in isolation.^[3]

Refractory CINV (recurring in a later cycle despite prior antiemetic prophylaxis): escalate rather than repeat the regimen that already failed — move to a full 4-drug regimen if not already using one, switch to palonosetron for its longer coverage, add olanzapine if it was not already included, and consider nabilone as an add-on for genuinely refractory symptoms.

Non-Pharmacologic Treatment

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.

Pharmacologic Treatment Options

Drug / intervention	Role	Dose / use	Important adverse effects	Teaching points
Ondansetron Preferred	5-HT3RA, acute-phase backbone for HEC/MEC/LEC prophylaxis	16-24 mg PO once daily, or up to 16 mg IV (max single IV dose 8 mg if age 75 or older)	Headache, constipation, dose-dependent QTc prolongation	Equivalent efficacy to granisetron. Avoid combining with other QTc-prolonging drugs.
Granisetron Preferred	5-HT3RA, alternative acute-phase backbone	2 mg PO once daily or 1 mg PO BID; 0.01 mg/kg IV (max 1 mg) once daily	Headache, constipation, dose-dependent QTc prolongation	Equivalent efficacy to ondansetron.
Palonosetron Preferred	2nd-generation 5-HT3RA — single dose covers acute and delayed MEC phases	0.25 mg IV single dose before chemotherapy starts	Headache, constipation, dose-dependent QTc prolongation	Substantially longer half-life than 1st-generation agents. Preferred when multi-day 5-HT3RA dosing is impractical.
Aprepitant Preferred	NK-1RA, HEC and high-risk MEC	125 mg PO Day 1, 80 mg PO once daily Days 2-3	Asthenia/fatigue, diarrhea, hiccups	Not used as monotherapy. Reduce dexamethasone dose by about half when co-administered — CYP3A4 inhibition.
Fosaprepitant Alternative	IV NK-1RA — single-dose alternative to 3-day oral aprepitant	150 mg IV once, Day 1 only, about 30 minutes before chemotherapy	Asthenia/fatigue, diarrhea, hiccups	Rapidly converted to aprepitant after infusion. Same dexamethasone dose-reduction rule applies.
Netupitant / palonosetron Preferred	Fixed NK-1RA + 5-HT3RA combination, single oral dose	300 mg netupitant / 0.5 mg palonosetron PO, single dose 1 hour before chemotherapy Day 1	Headache, constipation, fatigue	Simplifies HEC or high-risk-MEC prophylaxis to one dose. Same dexamethasone dose-reduction rule applies.
Dexamethasone Preferred	Corticosteroid backbone of every risk-tier regimen	12 mg PO/IV Day 1 (reduce to 8-12 mg if combined with an NK-1RA); 8 mg once daily Days 2-3 for non-AC HEC delayed phase	Insomnia, hyperglycemia, GI irritation, mood change	Limit to Day 1 only after an AC-based highly emetogenic regimen — a multi-day course is not needed there.
Olanzapine Preferred	4th agent in the HEC quadruple regimen; preferred breakthrough monotherapy	10 mg (or 5 mg) PO Day 1, continued Days 2-4; 10 mg PO once daily for 3 days for breakthrough	Sedation, orthostatic hypotension, weight gain	Additive CNS/respiratory depression with benzodiazepines. Avoid combining with metoclopramide — increased tardive dyskinesia risk.
Metoclopramide Alternative	Dopamine antagonist, LEC prophylaxis or breakthrough/refractory rescue	10-20 mg PO/IV Q4-6H PRN; high dose 1-3 mg/kg IV Q4-6H for refractory symptoms	Sedation, dose-related diarrhea, extrapyramidal effects	High-dose regimen is more effective than low dose but carries higher extrapyramidal risk.
Prochlorperazine Alternative	Dopamine antagonist, LEC or rescue — widest range of dosage forms	5-10 mg PO TID-QID; 25 mg PR Q12H; 2.5-10 mg IV/IM (not to exceed 40 mg/day)	Sedation, anticholinergic effects, extrapyramidal effects	Useful for outpatients who cannot reliably tolerate oral dosing.
Haloperidol Special situation	Refractory CINV — limited randomized-trial evidence but commonly used	1-2 mg PO Q4-6H PRN	Sedation, extrapyramidal effects, QTc prolongation	Avoid combining with other QTc-prolonging drugs. May be less effective than metoclopramide.
Lorazepam Special situation	Anticipatory CINV adjunct — never antiemetic monotherapy	0.5-2 mg PO/SL Q4-6H, or scheduled starting the night before the next chemotherapy cycle	Sedation	Always paired with behavioural technique and optimizing the prophylactic regimen for the next cycle.
Nabilone Special situation	Refractory CINV add-on	0.5 mg PO BID starting dose, titrated to 1-2 mg PO BID (max 6 mg/day)	Sedation, dizziness, psychotropic effects, tachycardia	Oral formulation only. First dose given the night before chemotherapy.
Dimenhydrinate Avoid	Not an effective CINV agent	Not recommended for CINV at any dose	Sedation	Effective for motion sickness only — no better than placebo for chemotherapy-induced nausea and vomiting.

Special Populations

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.

Monitoring & Follow-Up

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.

Treatment Failure / Next Step

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).
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.
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.
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.
For anticipatory symptoms, add a benzodiazepine before the next cycle and refer for behavioural techniques (systematic desensitization).
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.

Common Errors to Avoid

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.

Clinical Decision Algorithm

Selecting prophylaxis by emetogenic-risk tier

New chemotherapy regimen ordered; identify the regimen's single most emetogenic component

High risk (over 90%)

Day 1: 5-HT3RA + NK-1RA + dexamethasone 12 mg + olanzapine 10 mg

AC-based regimen

Days 2-4: olanzapine only; stop dexamethasone after Day 1

Non-AC regimen (e.g. cisplatin)

Days 2-4: continue dexamethasone + olanzapine; NK-1RA per its own course

Moderate risk (30-90%)

Day 1: 5-HT3RA + dexamethasone

High-risk MEC: carboplatin AUC 5+, oxaliplatin in women 50 or younger, select ADCs

Add an NK-1RA — triple therapy

Standard-risk MEC

Double therapy is sufficient; consider Days 2-3 dexamethasone or olanzapine for delayed phase

Low risk (10-30%)

Single agent, Day 1 only — dexamethasone, a 5-HT3RA, or a dopamine antagonist; no routine delayed-phase prophylaxis

Minimal risk (under 10%)

No routine prophylaxis; treat symptomatically only if symptoms occur

Managing symptoms that occur despite prophylaxis

Nausea or vomiting despite an antiemetic regimen already in place

Red flags present (dehydration, cannot tolerate oral therapy, QTc risk)

Escalate to IV antiemetics/fluids and urgent oncology assessment

Breakthrough — within 5 days despite optimal prophylaxis

Add a rescue agent from a different class, dosed on schedule; consider olanzapine 10 mg daily x 3 days if not already used

Reassess and escalate the prophylactic regimen for the next cycle

Anticipatory — before/at chemotherapy administration

Add lorazepam or alprazolam starting the night before/morning of the next cycle

Refer for systematic desensitization/behavioural therapy; optimize prophylaxis for next cycle

Refractory — recurs in later cycles despite prior adequate prophylaxis

Step up: ensure a full 4-drug HEC regimen, switch to palonosetron, add olanzapine if absent

Consider nabilone; consider haloperidol; refer to supportive oncology if still uncontrolled

Drug Tables

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.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Ondansetron	Acute, oral: 16-24 mg PO once daily Acute, IV: Up to 16 mg IV infused over at least 15 minutes; maximum single IV dose 8 mg if age 75 or older; subsequent IV doses up to 8 mg, may repeat 4 and 8 hours after the initial dose Pediatric: Weight-based dosing per institutional pediatric oncology antiemetic protocol	Bradycardia, constipation, diarrhea, dizziness, headache, dose-dependent QTc prolongation, transient LFT elevation	Avoid other QTc-prolonging drugs; avoid other serotonergic drugs or monitor closely for serotonin syndrome	Equivalent efficacy and toxicity to granisetron for acute-phase prevention.
Granisetron	Oral: 2 mg once daily, or 1 mg PO BID IV: 0.01 mg/kg (maximum 1 mg) once daily Pediatric: Weight-based dosing per institutional pediatric oncology antiemetic protocol	Bradycardia, constipation, diarrhea, dizziness, headache, dose-dependent QTc prolongation, transient LFT elevation	Avoid other QTc-prolonging drugs; avoid other serotonergic drugs or monitor closely for serotonin syndrome	Equivalent efficacy and toxicity to ondansetron for acute-phase prevention.
Palonosetron	IV, single dose per cycle: 0.25 mg IV once, before chemotherapy starts Pediatric: Weight-based dosing per institutional pediatric oncology antiemetic protocol	Bradycardia, constipation, diarrhea, dizziness, headache, dose-dependent QTc prolongation, transient LFT elevation	Avoid other QTc-prolonging drugs; avoid other serotonergic drugs or monitor closely for serotonin syndrome	Substantially longer half-life than first-generation 5-HT3 receptor antagonists, giving effective single-dose-per-cycle coverage into the delayed phase of MEC; preferred when multi-day first-generation dosing is impractical.^[9]

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.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Aprepitant	Day 1: 125 mg PO, 1 hour before chemotherapy Days 2-3: 80 mg PO once daily Pediatric: Weight-based dosing per institutional pediatric oncology antiemetic protocol	Asthenia/fatigue, diarrhea, dizziness, dyspepsia, hiccups	CYP3A4 substrate/inhibitor — reduce dexamethasone dose by about half; contraindicated with pimozide; may reduce hormonal contraceptive efficacy	Oral NK-1 receptor antagonist.
Fosaprepitant	Day 1 only: 150 mg IV infused over 20-30 minutes, about 30 minutes before chemotherapy Pediatric: Weight-based dosing per institutional pediatric oncology antiemetic protocol	Asthenia/fatigue, diarrhea, dizziness, dyspepsia, hiccups	Rapidly converted to aprepitant after infusion — same interaction profile; reduce dexamethasone dose by about half; contraindicated with pimozide	Single-dose IV alternative that may replace the entire 3-day oral aprepitant course.

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

Drug	Dosage	Adverse effects	Drug interactions	Comments
Netupitant / palonosetron	Day 1, single dose: 300 mg netupitant / 0.5 mg palonosetron PO, 1 hour before chemotherapy Pediatric: Not established — use individual-component dosing per pediatric oncology protocol instead	Headache, constipation, fatigue	Reduce dexamethasone dose by about half; contraindicated with pimozide; avoid other QTc-prolonging drugs, electrolyte-lowering drugs, or CYP3A4 inhibitors	Fixed-dose oral combination — simplifies HEC or high-risk-MEC prophylaxis to a single dose.

Corticosteroids

Drug	Dosage	Adverse effects	Drug interactions	Comments
Dexamethasone	Acute, Day 1: 12 mg PO/IV single dose (increase to 20 mg for HEC or MEC only if not combined with an NK-1 receptor antagonist; reduce to 8-12 mg when combined with aprepitant, fosaprepitant, or netupitant) Delayed, non-AC HEC: 8 mg PO once daily, Days 2-3 Delayed, AC-based HEC: None required — limited to Day 1 only Pediatric: Weight-based dosing per institutional pediatric oncology antiemetic protocol	Mood changes, increased appetite, GI irritation/ulceration, fluid retention, weight gain, may mask signs of infection	CYP3A4 substrate — inhibitors decrease its metabolism, inducers and antacids increase its metabolism; aprepitant/fosaprepitant/netupitant increase its serum concentration	Limit to Day 1 only after an AC-based highly emetogenic regimen; a multi-day course remains appropriate for non-AC highly emetogenic regimens.

Atypical Antipsychotic

Drug	Dosage	Adverse effects	Drug interactions	Comments
Olanzapine	Prophylaxis, Day 1: 10 mg PO before chemotherapy (5 mg if sedation is a concern) Prophylaxis, Days 2-4: 10 mg (or 5 mg) PO once daily Breakthrough monotherapy: 10 mg PO once daily for 3 days, if not already used for prophylaxis Pediatric: Not established for routine pediatric CINV dosing — specialist-directed only	Dizziness, constipation, postural hypotension, akathisia, somnolence, dry mouth; rare Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS)	Additive CNS/respiratory depression with benzodiazepines; increased tardive dyskinesia risk with metoclopramide; strong CYP1A2 inhibitors decrease its metabolism; may reduce antiparkinsonian-drug efficacy	Now a fixed 4th component of the standard highly-emetogenic-chemotherapy prophylactic regimen, and the single most evidence-supported agent for breakthrough CINV monotherapy.^[2]^[8]

Dopamine Antagonists

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

Drug	Dosage	Adverse effects	Drug interactions	Comments
Metoclopramide	Standard dose: 10-20 mg PO/IV Q4-6H PRN High dose (refractory/breakthrough): 1-3 mg/kg IV Q4-6H PRN, under close monitoring for extrapyramidal effects Pediatric: Weight-based dosing per institutional pediatric oncology antiemetic protocol; extrapyramidal-effect risk is higher in children — use cautiously	Sedation, dose-related diarrhea, extrapyramidal effects	Additive sedation with other sedating medications (opioids, hypnotics, alcohol); anticholinergic agents antagonize its effect on GI motility	High-dose regimen is significantly more effective than low dose but carries higher extrapyramidal risk.
Prochlorperazine	Oral: 5-10 mg PO TID-QID Rectal: 25 mg PR Q12H IV: 2.5-10 mg IV, not to exceed 40 mg/day IM: 5-10 mg IM initial dose, may repeat Q3-4H, not to exceed 40 mg/day Pediatric: Not established for routine pediatric use — specialist-directed only	Sedation, anticholinergic effects (dry mouth, blurred vision, constipation, nasal congestion, urinary retention), extrapyramidal effects, hypotension, rare pancytopenia	Additive sedation with other sedating medications (opioids, hypnotics, alcohol)	Widest range of dosage forms of any agent in this table — especially useful for outpatients who cannot reliably tolerate oral dosing.
Haloperidol	Oral: 1-2 mg PO Q4-6H PRN Pediatric: Not established for routine pediatric use — specialist-directed only	Sedation, extrapyramidal effects	Additive sedation with other sedating medications; avoid combining with other QTc-prolonging drugs when possible; CYP2D6/CYP3A4 inhibitors decrease its metabolism (avoid or monitor for toxicity), CYP3A4 inducers increase its metabolism (avoid or monitor for reduced effect)	Reasonable evidence for refractory CINV despite limited randomized-trial data; may be less effective than metoclopramide.

Benzodiazepines

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

Drug	Dosage	Adverse effects	Drug interactions	Comments
Lorazepam	Oral/sublingual: 0.5-2 mg PO/SL Q4-6H, or scheduled starting the night before or morning of the next chemotherapy cycle Pediatric: Not established for routine pediatric CINV use — specialist-directed only	Sedation	Additive sedation with other sedating medications (opioids, hypnotics, alcohol) — avoid or minimize concurrent use	Preferred benzodiazepine for anticipatory CINV given the stronger evidence base for this specific indication.
Alprazolam	Oral: 0.25-0.5 mg PO, standard anxiolytic dosing, starting before the next chemotherapy cycle Pediatric: Not established for pediatric CINV use	Sedation	Additive sedation with other sedating medications (opioids, hypnotics, alcohol) — avoid or minimize concurrent use	An alternative to lorazepam for anticipatory CINV; less first-line, since lorazepam has the stronger evidence base for this specific indication.

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.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Nabilone	Oral: 0.5 mg PO BID starting dose, titrated to 1-2 mg PO BID as tolerated, maximum 6 mg/day; first dose the night before chemotherapy, second dose 1-3 hours before chemotherapy Pediatric: Not established for routine pediatric use — specialist-directed only	Sedation, dizziness, ataxia, psychotropic effects, tachycardia, orthostatic hypotension, dry mouth	Additive sedation with other sedating medications (opioids, hypnotics, alcohol) — avoid or minimize concurrent use	Oral formulation only. Higher doses carry a higher risk of side effects.

Not effective for CINV: the antihistamine dimenhydrinate and the antimuscarinic scopolamine are useful for motion sickness but are no more effective than placebo for chemotherapy-induced nausea and vomiting specifically — do not substitute either for a guideline-concordant antiemetic regimen.

References

Antiemetics: ASCO Guideline Update — Journal of Clinical Oncology, American Society of Clinical Oncology (Hesketh PJ, Kris MG, Basch E, et al.). J Clin Oncol 2020;38(24):2782-2797
2023 updated MASCC/ESMO consensus recommendations: prevention of nausea and vomiting following high-emetic-risk antineoplastic agents — Supportive Care in Cancer, Multinational Association of Supportive Care in Cancer / European Society for Medical Oncology (Herrstedt J, Celio L, Hesketh PJ, et al.). Support Care Cancer 2023;32(1):47
Anticipatory nausea and vomiting — Supportive Care in Cancer (Roscoe JA, Morrow GR, Aapro MS, Molassiotis A, Olver I). Support Care Cancer 2011;19(10):1533-1538
Emetic risk classification and evaluation of the emetogenicity of antineoplastic agents—updated MASCC/ESMO consensus recommendation — Supportive Care in Cancer, Multinational Association of Supportive Care in Cancer / European Society for Medical Oncology (Jordan K, Chan A, Gralla RJ, et al.). Support Care Cancer 2023;32(1):53
2023 updated MASCC/ESMO consensus recommendations: prevention of nausea and vomiting following moderately emetic risk antineoplastic agents — Supportive Care in Cancer, Multinational Association of Supportive Care in Cancer / European Society for Medical Oncology (Scotté F, Schwartzberg L, Iihara H, et al.). Support Care Cancer 2023;32(1):45
2023 updated MASCC/ESMO consensus recommendations: controlling nausea and vomiting with chemotherapy of low or minimal emetic potential — Supportive Care in Cancer, Multinational Association of Supportive Care in Cancer / European Society for Medical Oncology (Olver I, Clark-Snow R, Ruhlmann CH, et al.). Support Care Cancer 2023
2023 updated MASCC/ESMO consensus recommendations: prevention of nausea and vomiting following multiple-day chemotherapy, high-dose chemotherapy, and breakthrough nausea and vomiting — Supportive Care in Cancer, Multinational Association of Supportive Care in Cancer / European Society for Medical Oncology (Rapoport BL, Herrstedt J, Snow RC, et al.). Support Care Cancer 2023;32(1):36
Olanzapine for the prevention and treatment of cancer-related nausea and vomiting in adults — Cochrane Database of Systematic Reviews (Sutherland A, Naessens K, Plugge E, et al.). Cochrane Database Syst Rev 2018;9(9):CD012555
Improved prevention of moderately emetogenic chemotherapy-induced nausea and vomiting with palonosetron, a pharmacologically novel 5-HT3 receptor antagonist: results of a phase III, single-dose trial versus dolasetron — Cancer (Eisenberg P, Figueroa-Vadillo J, Zamora R, et al.). Cancer 2003;98(11):2473-2482

Professional reference only. Apply clinical judgment and verify patient-specific decisions against current authoritative guidance and product information.