What is the best anti-nauseant (antiemetic) for patients with constipation?

From the Guidelines

For patients with constipation who need an antiemetic, ondansetron (Zofran) is generally the best choice. The typical adult dose is 4-8 mg orally every 8 hours as needed for nausea or vomiting. Ondansetron works by blocking serotonin receptors in the brain and gut that trigger nausea, without significantly affecting gut motility or worsening constipation. Unlike other common antiemetics such as metoclopramide (Reglan), prochlorperazine (Compazine), or promethazine (Phenergan), ondansetron doesn't cause constipation as a side effect and may actually slightly increase small intestinal transit 1.

Some key points to consider when choosing an antiemetic for patients with constipation include:

• The potential for the antiemetic to exacerbate constipation
• The efficacy of the antiemetic in preventing nausea and vomiting
• The side effect profile of the antiemetic

In the context of constipation, it's essential to select an antiemetic that does not worsen constipation. Ondansetron is a suitable option, as it does not significantly affect gut motility and is not associated with constipation as a side effect 1.

For patients with severe constipation, it's crucial to address the underlying constipation with appropriate treatments such as increased fluid intake, dietary fiber, physical activity, and laxatives if needed, while managing nausea with ondansetron. If ondansetron is ineffective or contraindicated, consider alternative antiemetics with minimal impact on constipation, such as scopolamine patches or ginger supplements. However, it's essential to note that the evidence for these alternatives is not as strong as for ondansetron 1.

In clinical practice, the goal is to balance the management of nausea and vomiting with the potential impact on constipation. By choosing ondansetron as the primary antiemetic, clinicians can minimize the risk of exacerbating constipation while effectively managing nausea and vomiting.

From the FDA Drug Label

The most common adverse reactions reported in greater than or equal to 4% of 300 adults receiving a single 24 mg dose of ondansetron tablets orally in 2 trials for the prevention of nausea and vomiting associated with highly emetogenic chemotherapy (cisplatin greater than or equal to 50 mg/m 2) were: headache (11%) and diarrhea (4%) The most common adverse reactions reported in 4 trials in adults for the prevention of nausea and vomiting associated with moderately emetogenic chemotherapy (primarily cyclophosphamide-based regimens) are shown in Table 3 Table 3: Most Common Adverse Reactions in Adults afor the Prevention of Nausea and Vomiting Associated with Moderately Emetogenic Chemotherapy [Primarily Cyclophosphamide-based Regimens] Adverse Reaction Ondansetron Tablets 8 mg Twice Daily (n = 242) Placebo (n = 262) Headache 58 (24%) 34 (13%) Malaise/Fatigue 32 (13%) 6 (2%) Constipation 22 (9%) 1 (<1%) Diarrhea 15 (6%) 10 (4%)

Ondansetron is associated with constipation in 9% of patients.

• The FDA drug label for ondansetron does not provide a comparison of the anti-nauseant with the best efficacy in patients with constipation.
• No conclusion can be drawn regarding the best anti-nauseant for patients with constipation based on the provided information 2.

From the Research

Anti-Nauseants and Constipation

When considering anti-nauseants for patients with constipation, it's essential to evaluate the potential side effects of these medications.

• Ondansetron, a commonly used anti-nauseant, has been shown to cause constipation in some patients 3.
• In a study comparing ondansetron to prochlorperazine for the prevention of nausea and vomiting in patients undergoing fractionated radiotherapy, constipation was seen more commonly with ondansetron 3.
• Another study found that ondansetron is more effective and produces fewer adverse events than metoclopramide for the prevention of emesis associated with high-dose cisplatin chemotherapy, but it may cause headache and constipation 4.
• A review of antiemetic therapy for nausea and vomiting in the emergency department found that ondansetron is as effective as promethazine and is not associated with sedation or akathisia, but its potential to cause constipation was not mentioned 5.
• A network meta-analysis of drugs for preventing postoperative nausea and vomiting in adults after general anesthesia found that ondansetron is one of the most effective single drugs for reducing vomiting, but its potential to cause constipation was not evaluated 6.

Alternative Options

Considering the potential for constipation with ondansetron, alternative anti-nauseants may be preferred for patients with constipation.

• Metoclopramide, which is often used for its prokinetic effects, may be a better option for patients with constipation, as it can help stimulate bowel movements 7, 4.
• Other anti-nauseants, such as granisetron or droperidol, may also be considered, although their effects on constipation are not well-studied 6.

It's crucial to weigh the benefits and risks of each anti-nauseant and consider individual patient factors, such as constipation, when selecting an appropriate medication.