PHARMACOLOGY

Pharmacotherapeutic Group: Anti-emetics

Pharmacodynamic properties: 

Ondansetron antagonizes selective 5-HT₃ receptor, blocking serotonin, both peripherally on vagal nerve terminals and centrally in the chemoreceptor trigger zone. This action of ondansetron gives its antiemetic property to prevent emesis due to acute chemotherapy mediated by serotonin.

Pharmacokinetic properties:

Absorption: Peak plasma concentrations, Oral: 1.5 hours. Bioavailability: 56-71%

Distribution: Extensively distributed. Protein binding: 70-75%

Metabolism: Hepatic via multiple enzymatic pathways

Excretion: Via urine (44-60% as metabolites, 5-10% as unchanged), faeces (approx 25%). Terminal elimination half-life: Oral/parenteral: 3 hours; rectal: 6 hours; elderly/renal impairment: prolonged, approx 5 hours; severe hepatic impairment: 15-32 hours.

 INDICATIONS

Chemotherapy induced nausea and vomiting, gastroenteritis, post operative nausea and vomiting, morning sickness

 DOSE

Adult: 4-8 mg twice daily.

CONTRAINDICATIONS

 Hypersensitivity, lactation

SPECIAL PRECAUTIONS

May cause QT prolongation; caution when used in cardiac diseases, patients who are on medications that can prolong QT or patients with electrolyte abnormalities. Severe hepatic impairment. May mask progressive ileus and/or gastric distension. Pregnancy, lactation

 ADVERSE DRUG REACTIONS

Headache, malaise, constipation, drowsiness, fever, anxiety, cold sensation, pruritus, diarrhoea, gynaecological disorder, urinary retention.

 DRUG INTERACTIONS

Rifampicin and other CYP3A4 inducers reduce effects of ondansetron.

Serious Drug Interaction: Concurrent use may increase the hypotensive effect of apomorphine.

 PRESENTATION

VOMISET 4: Each box is supplied with 10 strips of 10 tabs packed in blisters.

VOMISET 8: Each box is supplied with 10 strips of 10 tabs packed in blisters.