What is the diagnosis and management for a patient with dizziness and vomiting, possibly on prochlorperazine?

Differential Diagnosis and Initial Management of Dizziness and Vomiting

The most likely diagnoses for a patient presenting with dizziness and vomiting include vestibular disorders (such as benign paroxysmal positional vertigo, vestibular neuritis, or labyrinthitis), gastroparesis, cyclic vomiting syndrome, cannabis hyperemesis syndrome (particularly in younger patients), metabolic derangements (hypercalcemia, electrolyte disturbances), medication adverse effects, or central nervous system pathology. 1

Immediate Diagnostic Workup

Obtain complete blood count, comprehensive metabolic panel (including calcium), glucose, liver function tests, lipase, and urinalysis to exclude metabolic causes and assess for dehydration and electrolyte abnormalities. 1 These laboratory tests are critical because prolonged vomiting causes hypokalemia, hypochloremia, and metabolic alkalosis that require correction. 1

• Screen for cannabis use with urine drug testing, especially in patients under 50 years old, as Cannabis Hyperemesis Syndrome is increasingly common and requires specific management. 1
• Consider thyroid function tests and morning cortisol if clinically indicated to exclude hypothyroidism or Addison's disease. 1
• Perform one-time esophagogastroduodenoscopy or upper GI imaging to exclude obstructive lesions, but avoid repeated endoscopy unless new symptoms develop. 1

First-Line Pharmacologic Management

Initiate dopamine receptor antagonists as first-line therapy, specifically prochlorperazine 10-20 mg orally or IV 3-4 times daily, metoclopramide 10-20 mg orally or IV 3-4 times daily, or haloperidol 1 mg IV/PO every 4 hours as needed, titrated to maximum benefit and tolerance. 2, 3, 4, 5 Prochlorperazine is FDA-approved for severe nausea and vomiting and has demonstrated efficacy in multiple clinical settings. 5, 6

Critical Monitoring for Dopamine Antagonists

• Monitor for akathisia, which can develop at any time within 48 hours of administration, particularly in young males. 1, 7, 8 The incidence of akathisia with prochlorperazine is approximately 14% and manifests as restlessness and inability to sit still. 8
• Prophylactically administer diphenhydramine 50 mg IV with prochlorperazine to reduce akathisia risk by 61% (from 36% to 14%), though this increases sedation. 9
• Treat established akathisia immediately with diphenhydramine 50 mg IV. 1, 9
• Slow the infusion rate to reduce akathisia incidence. 7

Second-Line Therapy for Persistent Symptoms

If vomiting persists after 4 weeks of dopamine antagonist therapy at maximum tolerated doses, add ondansetron 8 mg orally or IV 2-3 times daily (maximum 16 mg per dose). 2, 1, 3 Ondansetron acts on different receptors (5-HT3) than dopamine antagonists, providing complementary antiemetic coverage. 3

• Use ondansetron sublingual tablets if the oral route is compromised by ongoing vomiting, as this formulation improves absorption. 2, 3
• Monitor for QTc prolongation when using ondansetron, especially in combination with other QT-prolonging agents. 1
• Consider adding dexamethasone 4-8 mg orally or IV 3-4 times daily, as the combination of ondansetron plus dexamethasone is superior to either agent alone. 2, 3

Alternative Routes and Formulations

When oral administration is not feasible due to ongoing vomiting, use rectal suppositories (prochlorperazine 25 mg rectally every 12 hours or promethazine 25 mg rectally every 4-6 hours) or intravenous/subcutaneous continuous infusions. 2, 3

Specific Etiologies Requiring Targeted Treatment

Gastroparesis or Gastric Stasis

• Continue metoclopramide as it promotes gastric emptying in addition to its antiemetic effects. 2, 3
• Add a proton pump inhibitor for concurrent gastritis or dyspepsia. 2, 1

Cannabis Hyperemesis Syndrome

• Do not withhold abortive and prophylactic therapy even with ongoing cannabis use, as treatments can still be effective. 1
• Definitive diagnosis requires 6 months of cannabis cessation or at least 3 typical cycle lengths without vomiting. 1
• Avoid stigmatizing patients; offer supportive counseling for cessation. 1

Metabolic Abnormalities

• Correct hypercalcemia urgently with IV fluids and bisphosphonates if present. 2, 3
• Aggressively replace potassium and magnesium to target normal ranges. 1
• Ensure adequate fluid intake of at least 1.5 L/day. 1

Critical Pitfalls to Avoid

• Never use antiemetics in suspected mechanical bowel obstruction, as this masks progressive ileus and gastric distension. 1, 3
• Do not perform repeated endoscopy or imaging studies without new symptoms developing. 1
• Administer antiemetics on a scheduled basis rather than as-needed, as prevention is far easier than treating established vomiting. 3
• Use agents from different drug classes simultaneously rather than sequential monotherapy, as no single agent has proven superior. 3
• Supplement with thiamin to prevent Wernicke's encephalopathy in patients with persistent vomiting. 1

Refractory Cases

For symptoms persisting despite combination therapy, consider adding haloperidol 1 mg IV every 4 hours, continuous IV/subcutaneous antiemetic infusions, or olanzapine as third-line options. 2, 3 Multiple concurrent agents in alternating schedules may be necessary. 3