From the Guidelines
Yes, Zofran (ondansetron) is effective as an antiemetic even if the patient is already vomiting. For adults, the typical dose is 4-8 mg orally or intravenously every 8-12 hours as needed, with a maximum daily dose of 24 mg. For children, dosing is weight-based, usually 0.1-0.15 mg/kg per dose. Zofran works by blocking serotonin (5-HT3) receptors in the chemoreceptor trigger zone and gastrointestinal tract, which helps stop the vomiting process even after it has begun. The medication takes effect within 30 minutes when given orally and within minutes when administered intravenously. For patients actively vomiting, the oral dissolving tablet (ODT) formulation placed on the tongue or intravenous administration may be more appropriate than standard oral tablets. Side effects may include headache, constipation, and occasionally QT interval prolongation on ECG, so caution is advised in patients with cardiac conditions or electrolyte abnormalities. According to the 2017 Infectious Diseases Society of America clinical practice guidelines for the diagnosis and management of infectious diarrhea 1, antinausea and antiemetic agents, such as ondansetron, may be given to facilitate tolerance of oral rehydration in children >4 years of age and in adolescents with acute gastroenteritis associated with vomiting. Additionally, studies have shown that ondansetron can reduce vomiting in children and reduce the need for hospitalization for rehydration 1.
Some key points to consider when using Zofran (ondansetron) as an antiemetic include:
- The medication is effective in reducing vomiting in patients with acute gastroenteritis 1
- The typical dose for adults is 4-8 mg orally or intravenously every 8-12 hours as needed, with a maximum daily dose of 24 mg
- For children, dosing is weight-based, usually 0.1-0.15 mg/kg per dose
- The medication takes effect within 30 minutes when given orally and within minutes when administered intravenously
- Side effects may include headache, constipation, and occasionally QT interval prolongation on ECG, so caution is advised in patients with cardiac conditions or electrolyte abnormalities.
It's also worth noting that the guideline update for MASCC and ESMO in the prevention of chemotherapy- and radiotherapy-induced nausea and vomiting recommends the use of 5-HT3 receptor antagonists, such as ondansetron, in combination with dexamethasone and an NK 1 receptor antagonist beginning before chemotherapy 1. However, this guideline is specific to the prevention of chemotherapy- and radiotherapy-induced nausea and vomiting, and may not be directly applicable to the treatment of acute gastroenteritis.
From the FDA Drug Label
- Clinical Studies 14. 1 Prevention of Chemotherapy-Induced Nausea and Vomiting Highly Emetogenic Chemotherapy In 2 randomized, double-blind, monotherapy trials, a single 24 mg oral dose of ondansetron was superior to a relevant historical placebo control in the prevention of nausea and vomiting associated with highly emetogenic cancer chemotherapy, including cisplatin greater than or equal to 50 mg/m2 The first trial compared oral doses of ondansetron 24 mg as a single dose, 8 mg every 8 hours for 2 doses, and 32 mg as a single dose in 357 adult cancer patients receiving chemotherapy regimens containing cisplatin greater than or equal to 50 mg/m2. The first or single dose was administered 30 minutes prior to chemotherapy A total of 66% of patients in the ondansetron 24 mg once-a-day group, 55% in the ondansetron 8 mg twice-a-day group, and 55% in the ondansetron 32 mg once-a-day group, completed the 24-hour trial period with 0 emetic episodes and no rescue antiemetic medications, the primary endpoint of efficacy
The effectiveness of Zofran (ondansetron) as an antiemetic if the patient is already vomiting is not directly addressed in the provided drug label. The studies described in the label focus on the prevention of nausea and vomiting associated with chemotherapy, with ondansetron administered before the start of chemotherapy.
- The label does not provide information on the use of ondansetron in patients who are already vomiting.
- Therefore, no conclusion can be drawn about the effectiveness of ondansetron in this specific scenario 2.
From the Research
Efficacy of Zofran as an Antiemetic
- Zofran, also known as ondansetron, is a highly selective 5-HT3 receptor antagonist used to prevent nausea and vomiting 3.
- Studies have shown that ondansetron is effective in reducing the incidence and severity of nausea and vomiting induced by cytotoxic drugs and radiation 3.
- In a randomized, double-blind comparison with placebo, ondansetron was found to be an effective antiemetic in 78% of patients suffering from postoperative nausea and vomiting 4.
Effectiveness in Patients Already Vomiting
- A study comparing ondansetron with metoclopramide and placebo for adults with undifferentiated emergency department nausea and vomiting found that ondansetron was effective in reducing nausea severity, but the difference from the placebo group did not reach significance 5.
- Another study found that ondansetron was effective in achieving cessation of vomiting in 81% of children with acute gastroenteritis, although the difference from metoclopramide was not significant 6.
- There is no direct evidence to suggest that Zofran is ineffective as an antiemetic if the patient is already vomiting, but its effectiveness may be influenced by the underlying cause of nausea and vomiting 5, 6.