NK1 Receptor Antagonists
NK1 receptor antagonists (NK1 RAs) block the binding of substance P at neurokinin-1 receptors in both the central nervous system and the GI tract. Substance P is the primary mediator of the delayed phase of CINV (24 to 120 hours after chemotherapy), though NK1 RAs also enhance control of the acute phase when added to 5-HT3 RA–based regimens. NK1 RAs are a cornerstone of antiemetic prophylaxis for both highly emetogenic chemotherapy (HEC) and, in select situations, moderately emetogenic chemotherapy (MEC).
Aprepitant (Oral)
| Parameter | Detail |
|---|
| Brand name | Emend |
| Mechanism | Selective, high-affinity NK1 receptor antagonist; crosses the blood-brain barrier |
| Dosing — HEC | Day 1: 125 mg PO given 1 hour before chemotherapy; Days 2–3: 80 mg PO once daily each morning |
| Dosing — MEC | Day 1: 125 mg PO; Days 2–3: 80 mg PO once daily (when NK1 RA is included) |
| Half-life | 9–13 hours |
| Metabolism | CYP3A4 substrate and moderate inhibitor; CYP2C9 inducer |
| Key drug interactions | Dexamethasone: reduces dexamethasone dose by ~50% when co-administered (e.g., from 20 mg to 12 mg on Day 1); Warfarin: may decrease INR — monitor closely for 2 weeks after aprepitant initiation; Oral contraceptives: may reduce efficacy — recommend backup contraception; Benzodiazepines metabolized by CYP3A4 (midazolam, triazolam): increased benzodiazepine levels |
| Common adverse effects | Fatigue, hiccups, diarrhea, constipation, headache, anorexia |
| Availability | 40 mg, 80 mg, 125 mg capsules; also available as oral suspension |
Fosaprepitant (Intravenous)
| Parameter | Detail |
|---|
| Brand name | Emend IV |
| Mechanism | Water-soluble phosphoryl prodrug of aprepitant; rapidly converted to aprepitant by phosphatases after IV administration |
| Dosing | 150 mg IV over 20–30 minutes on Day 1 only, given 30 minutes before chemotherapy. This single-dose replaces the 3-day oral aprepitant regimen. |
| Half-life | Fosaprepitant itself: ~2 minutes (rapid conversion); aprepitant: 9–13 hours |
| Drug interactions | Same as aprepitant (CYP3A4-mediated) |
| Common adverse effects | Infusion-site reactions (pain, erythema, thrombophlebitis), fatigue, headache, hiccups |
| Availability | 150 mg single-use vial for IV infusion |
Netupitant (Available as Fixed-Dose Combination)
| Parameter | Detail |
|---|
| Brand name | AKYNZEO (netupitant 300 mg + palonosetron 0.5 mg oral capsule); AKYNZEO IV (fosnetupitant 235 mg + palonosetron 0.25 mg IV formulation) |
| Mechanism | Highly selective NK1 receptor antagonist with extended duration of action |
| Dosing — Oral | 1 capsule (netupitant 300 mg/palonosetron 0.5 mg) PO, given approximately 1 hour before chemotherapy on Day 1 only |
| Dosing — IV | Fosnetupitant 235 mg/palonosetron 0.25 mg IV over 30 minutes, given approximately 30 minutes before chemotherapy on Day 1 only |
| Half-life | Netupitant: ~88 hours (long half-life; single dose provides coverage through the delayed period) |
| Metabolism | CYP3A4 substrate and moderate inhibitor |
| Drug interactions | Same class-effect interactions as aprepitant. Dexamethasone dose reduction required. |
| Common adverse effects | Headache, constipation, fatigue |
| Advantages | Single-dose administration covers both acute and delayed phases; fixed-dose combination with palonosetron simplifies regimen |
Rolapitant (Oral)
| Parameter | Detail |
|---|
| Brand name | Varubi |
| Mechanism | Selective, long-acting NK1 receptor antagonist |
| Dosing | 180 mg PO given 1–2 hours before chemotherapy on Day 1 only. No repeat dosing needed due to long half-life. |
| Half-life | ~180 hours (approximately 7 days) |
| Metabolism | Primarily CYP2D6; does not inhibit or induce CYP3A4 |
| Key drug interactions | Does NOT require dexamethasone dose reduction (unlike aprepitant and netupitant). However, it is a moderate CYP2D6 inhibitor — avoid co-administration with CYP2D6 substrates with narrow therapeutic indices (thioridazine). |
| Common adverse effects | Dizziness, headache, hiccups, decreased appetite |
| Advantages | No CYP3A4 interaction (no dexamethasone dose adjustment); ultra-long half-life for single-dose convenience |
| Availability | 90 mg tablets (2 tablets = 180 mg dose). Note: IV formulation was previously available but withdrawn due to anaphylaxis and infusion site reactions. |
5-HT3 Receptor Antagonists
5-HT3 receptor antagonists (5-HT3 RAs) block serotonin binding at 5-HT3 receptors on vagal afferents in the GI tract and in the CTZ. They are the primary agents for prevention of acute CINV and form the backbone of antiemetic regimens across all emetogenic risk levels.
Ondansetron
| Parameter | Detail |
|---|
| Brand name | Zofran |
| Dosing — IV | 8 mg or 0.15 mg/kg (max 16 mg) IV over 15 minutes, given 30 minutes before chemotherapy. Maximum single IV dose: 16 mg (FDA-mandated dose cap due to QTc prolongation risk at 32 mg doses). |
| Dosing — Oral | 8 mg PO twice daily on Day 1 (or 16 mg PO once, given 30 minutes before chemotherapy); 8 mg PO twice daily on Days 2–3 for delayed prophylaxis when used without NK1 RA |
| Half-life | 3–6 hours |
| Metabolism | CYP3A4, CYP1A2, CYP2D6 |
| Key adverse effects | Headache (most common; 10–25%), constipation, dizziness, QTc prolongation (dose-dependent; avoid IV doses >16 mg), serotonin syndrome (rare, with concurrent serotonergic agents) |
| Warnings | ECG monitoring recommended in patients with electrolyte abnormalities, congestive heart failure, bradyarrhythmias, or concurrent use of other QTc-prolonging medications |
| Availability | IV: 4 mg/2 mL vials; Oral: 4 mg, 8 mg tablets; 4 mg/5 mL oral solution; 4 mg, 8 mg orally disintegrating tablets (ODT) |
Granisetron
| Parameter | Detail |
|---|
| Brand name | Kytril (IV/oral); Sancuso (transdermal patch); Sustol (extended-release subcutaneous injection) |
| Dosing — IV | 1 mg IV (or 0.01 mg/kg, max 1 mg) over 30 seconds to 5 minutes, given 30 minutes before chemotherapy |
| Dosing — Oral | 2 mg PO once daily or 1 mg PO twice daily, starting 1 hour before chemotherapy |
| Dosing — Transdermal | One 3.1 mg/24-hour patch applied to the upper outer arm 24–48 hours before chemotherapy; worn for up to 7 days |
| Dosing — Extended-release SC | 10 mg SC injected into the abdomen at least 30 minutes before chemotherapy on Day 1; provides sustained release for ≥5 days |
| Half-life | IV/oral: 5–9 hours; Extended-release SC: ~24 hours (with sustained release from polymer) |
| Metabolism | CYP3A4, CYP1A1 |
| Key adverse effects | Headache, constipation, asthenia, QTc prolongation (generally less than ondansetron), injection site reactions (SC formulation) |
| Advantages | Transdermal formulation useful for multi-day regimens and patients with nausea/vomiting or poor oral intake; extended-release SC provides 5-day coverage with single injection |
Palonosetron
| Parameter | Detail |
|---|
| Brand name | Aloxi (IV); also available in AKYNZEO fixed-dose combination |
| Dosing — IV | 0.25 mg IV push over 30 seconds, given 30 minutes before chemotherapy on Day 1 only |
| Dosing — Oral | 0.5 mg PO given 1 hour before chemotherapy on Day 1 (available in AKYNZEO combination) |
| Half-life | ~40 hours (significantly longer than other 5-HT3 RAs) |
| Mechanism advantages | Higher 5-HT3 receptor binding affinity (~100-fold greater than ondansetron); allosteric binding and receptor internalization; exhibits positive cooperativity; activity against both acute and delayed CINV |
| Metabolism | CYP2D6 (primarily), CYP3A4, CYP1A2 |
| Key adverse effects | Headache, constipation, QTc prolongation (less risk than ondansetron) |
| Advantages | Preferred 5-HT3 RA for MEC regimens and when a single-day 5-HT3 RA is desired. Randomized trials have demonstrated superiority over ondansetron and granisetron in the delayed phase for MEC. |
Comparative Summary — 5-HT3 Receptor Antagonists
| Agent | Route | Day 1 Dose | Half-Life | Repeat Dosing Needed? | Relative 5-HT3 Affinity |
|---|
| Ondansetron | IV | 8 mg or 0.15 mg/kg (max 16 mg) | 3–6 h | Yes (q12h Days 2–3) | 1× (reference) |
| Ondansetron | PO | 8 mg q12h or 16 mg once | 3–6 h | Yes | 1× |
| Granisetron | IV | 1 mg | 5–9 h | Yes (may repeat on Days 2–3) | ~3× |
| Granisetron | PO | 2 mg once or 1 mg q12h | 5–9 h | Yes | ~3× |
| Granisetron | Patch | 3.1 mg/24 h | Sustained | No (worn up to 7 days) | ~3× |
| Granisetron | SC (ER) | 10 mg | Sustained ≥5 d | No | ~3× |
| Palonosetron | IV | 0.25 mg | ~40 h | No (single dose) | ~100× |
Corticosteroids
Dexamethasone
Dexamethasone is the most widely used corticosteroid in antiemetic regimens and is included in prophylactic protocols for all emetogenic risk levels except minimal risk. Its antiemetic mechanism is incompletely understood but likely involves inhibition of prostaglandin synthesis, reduction of serotonin release from the GI tract, and anti-inflammatory effects on the blood-brain barrier.
| Parameter | Detail |
|---|
| Dosing — HEC (with NK1 RA) | Day 1: 12 mg IV or PO (dose reduced from 20 mg due to CYP3A4 inhibition by aprepitant/netupitant); Days 2–4: 8 mg PO once daily |
| Dosing — HEC (with rolapitant) | Day 1: 20 mg IV or PO (no dose reduction needed — rolapitant does not inhibit CYP3A4); Days 2–4: 8 mg PO twice daily |
| Dosing — MEC | Day 1: 8 mg IV or PO; Days 2–3: 8 mg PO once daily (if delayed prophylaxis indicated) |
| Dosing — LEC | 8 mg IV or PO on Day 1 only (alternative: 4 mg) |
| Half-life | Biological half-life: 36–54 hours |
| Key adverse effects (short-term use) | Insomnia (very common; consider morning dosing), hyperglycemia (monitor in diabetic patients), mood changes (agitation, anxiety, euphoria), dyspepsia, increased appetite, facial flushing |
| Key adverse effects (prolonged/repeated use) | Immunosuppression, adrenal suppression, myopathy, osteoporosis, hyperglycemia, weight gain |
| Drug interactions | Reduced clearance when co-administered with CYP3A4 inhibitors (aprepitant, netupitant) — dose adjustment required; increased clearance with CYP3A4 inducers (phenytoin, rifampin) |
| Special considerations | Dexamethasone may be omitted from regimens for patients receiving concurrent corticosteroids as part of their chemotherapy (e.g., prednisone-containing lymphoma regimens such as R-CHOP). In patients with diabetes, close glucose monitoring and possible insulin dose adjustment are required. |
Olanzapine
Olanzapine is an atypical antipsychotic that blocks multiple receptor types implicated in the emetic pathway, including dopamine D1, D2, D3, and D4 receptors; serotonin 5-HT2a, 5-HT2c, 5-HT3, and 5-HT6 receptors; histamine H1 receptors; and muscarinic M1–M3 receptors. Its broad receptor blockade profile makes it uniquely effective for both nausea and vomiting. A landmark randomized, double-blind, placebo-controlled trial demonstrated that adding olanzapine 10 mg to a standard three-drug regimen (NK1 RA + 5-HT3 RA + dexamethasone) significantly improved the proportion of patients with no nausea in both the acute and delayed periods after HEC.
| Parameter | Detail |
|---|
| Dosing — As part of 4-drug HEC prophylaxis | 5 mg or 10 mg PO once daily on Days 1–4. The 5 mg dose is increasingly recommended to reduce sedation while maintaining efficacy, supported by randomized non-inferiority data. |
| Dosing — Breakthrough CINV | 10 mg PO once daily for 3 days |
| Half-life | 21–54 hours (mean ~33 hours) |
| Key adverse effects | Sedation/somnolence (most significant; occurs in 35–70% at 10 mg dose, substantially less at 5 mg); weight gain (with repeated use); dizziness; dry mouth; hyperglycemia (monitor in diabetic patients); rare: QTc prolongation, neuroleptic malignant syndrome |
| Contraindications and cautions | Use with caution in elderly patients (fall risk from sedation), patients with Parkinson’s disease, patients with dementia (boxed warning for increased mortality in elderly patients with dementia-related psychosis), and patients with diabetes |
| Practical considerations | Administer at bedtime to minimize daytime sedation. The 5 mg dose is preferred for most patients and is endorsed by updated guideline recommendations. Available as 2.5 mg, 5 mg, 7.5 mg, 10 mg, 15 mg, 20 mg tablets. |
Dopamine Receptor Antagonists
Metoclopramide
| Parameter | Detail |
|---|
| Brand name | Reglan |
| Mechanism | D2 receptor antagonist (central and peripheral); also has weak 5-HT3 antagonism at high doses; prokinetic effects via 5-HT4 agonism |
| Dosing — Breakthrough/rescue | 10–20 mg PO or IV every 4–6 hours as needed (max 60 mg/day for standard dosing) |
| Dosing — High-dose (historical) | 1–2 mg/kg IV every 2–4 hours (largely replaced by 5-HT3 RAs but occasionally used in refractory settings) |
| Half-life | 5–6 hours |
| Key adverse effects | Extrapyramidal symptoms (EPS): acute dystonia (more common in young patients), akathisia, parkinsonism; tardive dyskinesia (FDA boxed warning with chronic use >12 weeks); sedation, diarrhea |
| Warnings | FDA boxed warning for tardive dyskinesia with prolonged use. Avoid in patients with Parkinson’s disease. Prophylactic diphenhydramine (25–50 mg) may be administered to reduce EPS risk when using high doses. |
Prochlorperazine
| Parameter | Detail |
|---|
| Brand name | Compazine |
| Mechanism | Phenothiazine; D2 receptor antagonist in the CTZ |
| Dosing — Oral | 5–10 mg PO every 6–8 hours as needed |
| Dosing — IV | 5–10 mg IV every 6–8 hours (max 40 mg/day) |
| Dosing — Rectal | 25 mg suppository every 12 hours |
| Half-life | 6–8 hours |
| Key adverse effects | EPS (dystonia, akathisia), sedation, hypotension, anticholinergic effects |
| Role | Primarily used for breakthrough CINV; limited role in primary prophylaxis in the era of modern antiemetics |
Haloperidol
| Parameter | Detail |
|---|
| Mechanism | Butyrophenone; potent D2 receptor antagonist |
| Dosing | 0.5–2 mg PO or IV every 4–6 hours as needed for breakthrough/refractory CINV |
| Key adverse effects | EPS, QTc prolongation, sedation |
| Role | Rescue/breakthrough setting only |
Benzodiazepines
Benzodiazepines enhance GABAergic inhibition in the CNS and are used primarily for anticipatory CINV, as anxiolytics during chemotherapy, and as adjuncts to standard antiemetic regimens. They have limited intrinsic antiemetic efficacy and should not be used as monotherapy for CINV prophylaxis.
Lorazepam
| Parameter | Detail |
|---|
| Brand name | Ativan |
| Dosing | 0.5–2 mg PO, IV, or sublingual every 4–6 hours as needed; for anticipatory CINV, 0.5–2 mg PO the night before and morning of chemotherapy |
| Half-life | 10–20 hours |
| Metabolism | Glucuronidation (no CYP450 involvement — advantage in polypharmacy) |
| Key adverse effects | Sedation, amnesia, dizziness, respiratory depression (especially with opioids), dependence with chronic use |
| Role | Primary agent for anticipatory CINV; adjunct to standard prophylactic regimens |
Alprazolam
| Parameter | Detail |
|---|
| Dosing | 0.25–0.5 mg PO two to three times daily starting the day before chemotherapy |
| Half-life | 6–12 hours |
| Role | Alternative to lorazepam for anticipatory CINV; less commonly used |
Cannabinoids
Cannabinoids activate CB1 and CB2 receptors in the CNS, including in the dorsal vagal complex and area postrema. They are recommended for breakthrough and refractory CINV when standard agents have failed. They are not recommended as first-line prophylaxis.
Dronabinol
| Parameter | Detail |
|---|
| Brand name | Marinol |
| Mechanism | Synthetic delta-9-tetrahydrocannabinol (THC); CB1 receptor agonist |
| Dosing | 5 mg/m² PO given 1–3 hours before chemotherapy, then every 2–4 hours as needed (max 6 doses/day); alternatively, 2.5–5 mg PO twice daily |
| Half-life | 25–36 hours (extensive tissue distribution) |
| Key adverse effects | Sedation/drowsiness, euphoria/dysphoria, dizziness, disorientation, impaired concentration, dry mouth, orthostatic hypotension, tachycardia |
| Cautions | Psychotomimetic effects (hallucinations, paranoia) more common in elderly and cannabinoid-naive patients; Schedule III controlled substance |
Nabilone
| Parameter | Detail |
|---|
| Brand name | Cesamet |
| Mechanism | Synthetic cannabinoid; CB1 receptor agonist |
| Dosing | 1–2 mg PO twice daily; first dose given 1–3 hours before chemotherapy; may be given the night before. Maximum: 6 mg/day in divided doses. |
| Half-life | ~2 hours (parent compound); active metabolites: longer |
| Key adverse effects | Sedation, vertigo, euphoria, dysphoria, dry mouth, visual disturbances, concentration difficulty |
| Advantages over dronabinol | Better oral bioavailability, more predictable pharmacokinetics |
Other Agents Used in CINV Management
Scopolamine (Transdermal)
| Parameter | Detail |
|---|
| Dosing | 1.5 mg transdermal patch applied behind the ear every 72 hours |
| Mechanism | Muscarinic M1 receptor antagonist; primarily effective against vestibular and motion-related components of nausea |
| Adverse effects | Dry mouth, blurred vision, urinary retention, confusion (especially in elderly) |
| Role | Adjunct for refractory nausea, particularly when a vestibular component is suspected |
Promethazine
| Parameter | Detail |
|---|
| Dosing | 12.5–25 mg PO, IV, IM, or rectal every 4–6 hours |
| Mechanism | Phenothiazine with H1 antihistamine and anticholinergic properties |
| Adverse effects | Sedation, EPS (less common than with prochlorperazine), tissue necrosis with extravasation (IV) |
| Warnings | FDA boxed warning regarding IV administration: severe tissue injury with inadvertent perivascular or intra-arterial injection. Preferred routes are PO, IM, or rectal. |
Gabapentin
| Parameter | Detail |
|---|
| Dosing | 300 mg PO on the night before chemotherapy, then 300 mg PO three times daily on Days 1–5 (studied doses) |
| Mechanism | Calcium channel alpha-2-delta subunit modulator; mechanism of antiemetic effect not fully elucidated |
| Evidence | Limited evidence suggests benefit as an adjunct, particularly for delayed nausea. Not yet incorporated into major guideline recommendations as standard therapy. |
References