Ondansetron
Ondansetron is a highly effective, centrally and peripherally acting **antiemetic** belonging to the 5-HT3 receptor antagonist class. Key clinical highlights: * **Refractory Vomiting**: Often utilized as a rescue or second-line antiemetic when conventional therapies (like maropitant or metoclopramide) are insufficient. * **Chemotherapy & Severe Disease**: Considered a gold standard for preventing and treating chemotherapy-induced nausea and vomiting (CINV), particularly with highly emetogenic drugs like cisplatin. It is also widely used in severe cases of **parvoviral enteritis**, **pancreatitis**, and **uremia**. * **Species Considerations**: Generally well-tolerated in dogs. Its use in cats has historically been debated, but it is frequently used in feline practice for intractable vomiting and severe pancreatitis with good clinical success. > **Clinical Pearl**: Ondansetron does not possess prokinetic properties. If gastric stasis or ileus is present, it will not resolve the motility issue and may mask underlying gastric distention.
กลไกการออกฤทธิ์: Ondansetron is a highly selective and competitive **5-HT3 (serotonin type 3) receptor antagonist**. * **Peripheral Action**: Cytotoxic drugs, severe inflammation (e.g., pancreatitis), or viral infections (e.g., parvovirus) cause cellular damage in the GI tract, triggering the release of serotonin from enterochromaffin cells. This serotonin binds to 5-HT3 receptors on vagal afferent nerve terminals, sending emetogenic signals to the brain. Ondansetron blocks these peripheral receptors. * **Central Action**: It also directly antagonizes 5-HT3 receptors located in the **Chemoreceptor Trigger Zone (CTZ)** within the area postrema of the brainstem, preventing central emetic signaling to the vomiting center. * **Net Effect**: Profound inhibition of the vomiting reflex without altering GI motility or causing significant sedation.
ขนาดยาตามชนิดสัตว์
- Empiric dose · 0.5 mg/kg IV or PO twice daily. · IV/PO · q12h
- Anti-emetic for intractable vomiting · 0.1-0.15 mg/kg slow IV push q6-12h as needed · IV · q6-12h · as needed
- Antiemetic for adjunctive treatment of severe pancreatitis · 0.1-1 mg/kg PO or IV q12-24h · PO/IV · q12-24h
- All uses (nausea and vomiting) · 0.5 mg/kg loading dose followed by 0.5 mg/kg/h infusion · IV · infusion for 6 hours · 6 hours · Used when signs are not controlled by other drugs.
- All uses (nausea and vomiting) · 0.5-1 mg/kg · PO · q12-24h · As needed · Oral bioavailability is considered to be low. Subcutaneous administration is more bioavailable.
- Severe vomiting (including parvovirus or pancreatitis) · 0.1-0.3 mg/kg IV given as a slow push every 8 to 12 hours (based on patient response). · IV · q8-12h · Has produced dramatic results in controlling or decreasing frequency of vomiting.
- Chemotherapy-related vomiting · 0.5-1 mg/kg PO q8-12h; 0.1-0.5 mg/kg IV over 15 minutes q8h or 30 minutes before cisplatin infusion. · PO/IV · q8-12h
- Adjunctive therapy of acute diarrhea · 0.5-1 mg/kg PO twice daily. · PO · q12h · Antagonizes neuronal 5-HT3 receptors and inhibits Cl- and H2O secretion from intestinal epithelial cells.
- Antiemetic · 0.1-0.2 mg/kg IV q6-12h or 0.1-1 mg/kg PO q1224h · IV/PO · q6-12h (IV) or q12-24h (PO)
วิธีการให้ยา
ข้อห้ามใช้
- Hypersensitivity to ondansetron or other 5-HT3 antagonists
- Concurrent use with apomorphine (due to risk of severe hypotension)
- Intestinal obstruction
อาการไม่พึงประสงค์
- Constipation
- Sedation
- Extrapyramidal clinical signs (head shaking)
- Arrhythmias
- Hypotension
- Headaches (reported in humans)
- Alterations in liver enzymes
- Hypersensitivity reactions (rare)
อันตรกิริยาระหว่างยา
- Apomorphine · Severe hypotension reported in humans; concurrent use is contraindicated.
- Drugs affecting QTc interval (e.g., amiodarone, cisapride, halothane, isoflurane, sotalol) · Theoretically may have additive effects on QTc interval, potentially resulting in serious arrhythmias.
- Tramadol · May reduce the efficacy of both drugs (human data); veterinary significance is unknown. · moderate
การติดตาม
- Clinical efficacy (reduction or cessation of vomiting)
- Hydration status and electrolyte balance (due to underlying vomiting)
- Resolution of nausea and vomiting
- Liver enzymes (with prolonged use)
- Bowel movements (monitor for constipation)
การได้รับยาเกินขนาด
Overdoses of up to 10X did not cause significant morbidity in human subjects. If an overdose occurs, treat supportively.
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