Can I give Reglan (metoclopramide) to someone on olanzapine?

Metoclopramide and Olanzapine: Contraindicated Combination

Metoclopramide (Reglan) should not be administered to patients taking olanzapine due to the risk of excessive dopamine blockade, which can lead to severe extrapyramidal symptoms and potentially dangerous adverse effects. 1

Mechanism of Interaction

The contraindication between these medications stems from their overlapping mechanisms of action:

• Olanzapine: An atypical antipsychotic that blocks multiple neuronal receptors including dopamine receptors 2
• Metoclopramide (Reglan): A dopamine receptor antagonist used for nausea and vomiting 1

When used together, these medications can cause:

• Excessive dopamine blockade
• Increased risk of extrapyramidal symptoms
• Potentially severe movement disorders
• Increased sedation

Clinical Guidelines Supporting This Contraindication

The Journal of the National Comprehensive Cancer Network (NCCN) guidelines specifically warn against using olanzapine concurrently with metoclopramide, stating:

"To avoid excessive dopamine blockade, clinicians should be cautious when using olanzapine concurrently with metoclopramide, phenothiazines, or haloperidol." 1

Alternative Antiemetic Options

For patients on olanzapine requiring antiemetic therapy, consider these alternatives:

1. 5-HT3 Receptor Antagonists:

   • Ondansetron
   • Granisetron
   • Palonosetron

2. NK1 Receptor Antagonists:

   • Aprepitant
   • Fosaprepitant

3. Other Options:

   • Dexamethasone
   • Lorazepam or alprazolam
   • Dronabinol or nabilone 1

Management Recommendations

If antiemetic therapy is needed for a patient on olanzapine:

1. First-line: Use a 5-HT3 antagonist with dexamethasone
2. Second-line: Consider NK1 receptor antagonists
3. Third-line: Consider benzodiazepines for breakthrough nausea
4. Never combine: Metoclopramide with olanzapine

Important Considerations

• The risk of extrapyramidal symptoms is significantly higher when dopamine antagonists are combined 3
• Elderly patients are at particularly high risk for adverse effects from this combination 3
• Patients with a history of movement disorders are at even greater risk
• Monitor for signs of sedation, confusion, and extrapyramidal symptoms if any antiemetic is used with olanzapine

Common Pitfalls to Avoid

1. Assuming that because both medications are used individually for nausea, they can be safely combined
2. Overlooking the pharmacological interaction between these medications
3. Failing to recognize early signs of extrapyramidal symptoms
4. Not considering alternative antiemetic options with different mechanisms of action

Remember that patient safety must be prioritized over convenience when selecting antiemetic therapy for patients already taking olanzapine.