Emiston8 mg/4 ml

Established / FDA-approved uses

• Prevention of chemotherapy-induced nausea and vomiting (CINV) — for initial and repeat courses of highly and moderately emetogenic cancer chemotherapy.
• Prevention of radiotherapy-induced nausea and vomiting — including total body irradiation, single high-dose fractions, and daily fractionated radiotherapy to the abdomen.
• Prevention and treatment of postoperative nausea and vomiting (PONV).

Off-label / commonly used, non-approved indications

• Nausea and vomiting due to acute gastroenteritis (particularly in children), based on clinical practice guidance rather than a formal approved indication.
• Nausea and vomiting in other clinical settings (e.g. hyperemesis gravidarum) used per clinician judgment when standard first-line options are inadequate; this use requires individualized risk-benefit discussion (see Pregnancy and Lactation).

Emiston is not indicated for routine prevention or treatment of nausea unrelated to the above settings.

Ondansetron is available (as ondansetron or ondansetron hydrochloride) in several dosage forms and strengths, including:

• Film-coated tablets: 4 mg, 8 mg
• Orally disintegrating tablets (ODT): 4 mg, 8 mg
• Oral solution/syrup: 4 mg/5 mL
• Injection (IV/IM): 2 mg/mL, commonly supplied as 4 mg/2 mL ampoules

Exact available strengths and formulations may vary by manufacturer and market.

Emiston is a selective serotonin 5-HT3 receptor antagonist used mainly as an antiemetic to preventand treat nausea and vomiting associated with cancer chemotherapy, radiotherapy, and surgery. It works by blockingserotonin receptors both in the central nervous system (chemoreceptor trigger zone) and peripherally on vagal nerveendings in the gastrointestinal tract, interrupting the reflex pathway that triggers vomiting.

Emiston does not stimulate gastrointestinal motility and is not a substitute for nasogastricsuction where that is clinically indicated.

Antiemetic — Selective serotonin 5-HT3 receptor antagonist

Pharmacodynamics

Ondansetron is a potent, highly selective antagonist of the 5-HT3 (serotonin type 3) receptor. Cytotoxicchemotherapy and radiotherapy cause release of serotonin from enterochromaffin cells in the small intestine, whichstimulates vagal afferents via 5-HT3 receptors, triggering the vomiting reflex; Ondansetron blocks this pathway bothperipherally and centrally at the chemoreceptor trigger zone. Ondansetron has no effect on dopamine receptors anddoes not have significant prokinetic activity.

Pharmacokinetics

• Absorption: Well absorbed orally; bioavailability is increased somewhat by a first-pass effect saturating with repeated dosing.
• Distribution: Approximately 70–76% plasma protein bound.
• Metabolism: Extensively metabolized in the liver, primarily via cytochrome P450 enzymes (CYP3A4, CYP2D6, CYP1A2); Ondansetron itself does not significantly induce or inhibit these enzymes.
• Elimination half-life: Approximately 3–4 hours in healthy adults, longer in hepatic impairment.
• Excretion: Mainly as metabolites in urine; renal clearance of unchanged drug accounts for a small fraction of total elimination.

• Tablets/oral solution: May be taken with or without food. Swallow tablets with water.
• Orally disintegrating tablets (ODT): Take with dry hands, place on the tongue, allow to dissolve, then swallow with saliva; no water is needed.
• Injection: Administered by a healthcare professional via slow intravenous or intramuscular injection; IV doses are typically diluted and given over at least 15 minutes when higher single doses are used.
• Timing: The first dose is generally given 30 minutes to 2 hours before the emetogenic stimulus (chemotherapy, radiotherapy, or anaesthesia induction), with further doses at defined intervals as above.
• If a dose of Emiston used for a scheduled course is missed, take it as soon as remembered unless it is almost time for the next dose; do not double the dose.

Clinically significant interactions

• Apomorphine: Concurrent use is contraindicated — reports of profound hypotension and loss of consciousness when apomorphine was given with Emiston.
• QT-prolonging drugs (e.g. certain antiarrhythmics, antipsychotics, some antibiotics such as fluoroquinolones or macrolides): Additive risk of QT prolongation and torsade de pointes; avoid combining where possible and use ECG monitoring if co-administration is necessary (see Precautions and Warnings).
• Serotonergic drugs (e.g. SSRIs, SNRIs, MAO inhibitors, tramadol, triptans): Increased risk of serotonin syndrome when combined with Emiston; monitor for agitation, hyperreflexia, autonomic instability, and altered mental status.
• Tramadol: May reduce the analgesic effect of tramadol and has been associated with increased patient-controlled tramadol use post-operatively.
• Potent CYP3A4 inducers (e.g. phenytoin, carbamazepine, rifampicin): May increase the metabolic clearance of Emiston, potentially reducing its effect; clinical dose adjustment is not routinely required but reduced efficacy should be watched for.

Common

• Headache
• Constipation
• Diarrhea
• Fatigue/malaise

Less common

• Dizziness
• Transient elevations in liver enzymes
• Flushing, hiccups

Rare but serious

• Hypersensitivity reactions, including anaphylaxis, angioedema, and bronchospasm
• QT interval prolongation and, rarely, torsade de pointes (see Precautions and Warnings)
• Transient visual disturbances, including temporary blindness (usually reversible)
• Extrapyramidal reactions (e.g. oculogyric crisis) without persistent sequelae
• Serious skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis) — rare

Pregnancy

Emiston should be used during pregnancy only if clearly needed and if the potential benefit justifies thepotential risk to the fetus; a physician should always be consulted before use in pregnancy. Some observationalstudies have suggested a small increased risk of certain birth defects (such as orofacial clefts) with first-trimesteruse of Emiston, although data are not entirely consistent and a definite causal relationship has not beenestablished. Animal reproduction studies have not shown harm to the fetus, but adequate, well-controlled studies inpregnant women are limited.

Lactation

Emiston is excreted in animal breast milk; it is not known whether it is excreted in human breast milk.Caution is advised, and a physician should be consulted to weigh the benefits of treatment against any potential riskto a breastfeeding infant.

• QT prolongation: Emiston can prolong the QT interval in a dose-dependent manner. Avoid in patients with congenital long QT syndrome. Use with caution in patients with electrolyte abnormalities (hypokalemia, hypomagnesemia), congestive heart failure, bradyarrhythmias, or those taking other QT-prolonging medications; ECG monitoring may be considered in at-risk patients.
• Serotonin syndrome: Risk increases when Emiston is combined with other serotonergic drugs (see Interactions); discontinue if symptoms occur and seek medical attention.
• Masking of underlying conditions: Emiston can mask progressive ileus or gastric distension following abdominal surgery or with chemotherapy-induced nausea; it is not a substitute for nasogastric suction when clinically indicated.
• Hypersensitivity: Use with caution in patients known to be hypersensitive to other selective 5-HT3 receptor antagonists, due to possible cross-sensitivity.
• Hepatic impairment: Dose should not exceed 8 mg/day in severe hepatic impairment (see Dosage and Administration).

There is no specific antidote for Emiston overdose. Reported effects of overdose include sudden transientblindness, severe constipation, hypotension, and a vasovagal episode with transient second-degree AV block; QTprolongation has also been reported. If overdose is suspected, seek immediate medical attention or contact a poisoncontrol center; management is supportive and symptomatic, with ECG monitoring where appropriate. Do not attemptspecific home treatment for a suspected overdose of Emiston.

Store at room temperature (below 30°C), away from light and moisture. Keep out of reach of children.

• Pediatric use: Safety and efficacy of Emiston are established for chemotherapy-induced nausea and vomiting in children 6 months and older (age/weight-based dosing) and for postoperative nausea and vomiting in children over 1 month of age (limited data); safety and efficacy in children below these age thresholds have not been established.
• Elderly: No dosage adjustment is generally required based on age alone, but age-related decline in hepatic or renal function should be considered.
• Renal impairment: No dosage adjustment is generally required.
• Hepatic impairment: In severe hepatic impairment, total daily dose of Emiston should not exceed 8 mg due to reduced clearance.
• Cardiac disease/electrolyte disturbance: Use with caution due to QT-prolongation risk (see Precautions and Warnings).

Duration depends on indication: for chemotherapy- or radiotherapy-induced nausea, Emiston is typicallyused for the day(s) of treatment and for 1–2 days afterward as needed, following the specific regimen prescribed. Forpostoperative nausea and vomiting, a single dose is usually sufficient. Emiston is not intended for long-termcontinuous use; if nausea persists beyond the expected course, the patient should be reassessed by a physician.

Serotonin 5-HT3 receptor antagonists (antiemetics)

Ondansetron selectively and competitively blocks 5-HT3 receptors located on vagal afferent nerve terminals inthe gut and in the area postrema/chemoreceptor trigger zone of the brainstem. By preventing serotonin (released fromenterochromaffin cells during chemotherapy, radiotherapy, or surgical stimulation) from activating these receptors,Ondansetron interrupts the afferent signalling that would otherwise trigger the vomiting reflex, thereby preventingor reducing nausea and vomiting.

B

Emiston is approved for prevention of chemotherapy-induced nausea and vomiting in children 6 months ofage and older, with dosing based on age/weight as detailed in Dosage and Administration. It is also used forprevention and treatment of postoperative nausea and vomiting in children, with data supporting use from about 1 monthof age for this indication in some formulations, though data are more limited than in adults. Emiston issometimes used off-label for nausea and vomiting due to acute gastroenteritis in children, per clinical judgment andlocal guidelines. Safety and efficacy of Emiston have not been established below the studied age thresholdsfor each indication, and a pediatrician should guide use in young children.