What is the recommended dosage of Gravol (dimenhydrinate) for nausea and vomiting?

Gravol (Dimenhydrinate) Dosing for Nausea and Vomiting

For adults with nausea and vomiting, administer dimenhydrinate 50 mg intramuscularly or intravenously every 4 hours as needed, with a maximum of 100 mg every 4 hours when drowsiness is acceptable; for oral administration, use 25-50 mg three times daily. 1, 2

Adult Dosing

Parenteral Administration

• Intramuscular route: 50 mg (1 mL) injected every 4 hours as needed 1
• Intravenous route: 50 mg diluted in 10 mL of 0.9% Sodium Chloride, injected over 2 minutes, every 4 hours 1
• Higher dose option: 100 mg every 4 hours may be used when drowsiness is not objectionable or is desirable 1
• Duration of action: Approximately 4 hours of symptom control per 50 mg dose 1

Oral Administration

• Standard dose: 25-50 mg three times daily 2
• Long-acting formulation (Gravol L/A): Contains 25 mg immediate-release plus 50 mg sustained-release dimenhydrinate, providing extended coverage 3

Pediatric Dosing

Parenteral Administration

• Intramuscular route: 1.25 mg/kg body weight OR 37.5 mg/m² body surface area, administered four times daily 1
• Maximum daily dose: 300 mg per day 1
• Important contraindication: Injectable form is contraindicated in neonates due to benzyl alcohol content 1

Clinical Context and Efficacy

Comparative Effectiveness

• Dimenhydrinate demonstrates moderate antiemetic efficacy, with studies showing reduction in nausea/vomiting scores from 8.6 to 3.8 in early pregnancy 4
• When used alone for postoperative nausea and vomiting (PONV), dimenhydrinate reduced incidence to 34.5% compared to 41.3% with placebo, though this difference was not statistically significant 5
• Combination therapy is more effective: Dimenhydrinate combined with droperidol reduced PONV to 19.6% and showed synergistic effects 5

Route Selection Considerations

• Use parenteral route when: Oral administration is impractical due to active vomiting or inability to tolerate oral medications 1
• Oral long-acting formulation: Particularly useful for outpatient procedures requiring extended prophylaxis, with preoperative administration providing coverage through the postoperative period 3

Important Safety Considerations

Common Adverse Effects

• Drowsiness: Expected with therapeutic dosing; may be dose-dependent 1
• Patients should be counseled about sedation, especially when higher doses (100 mg) are used 1

Toxicity Threshold

• Pediatric patients <6 years: Refer to emergency department if ingestion ≥7.5 mg/kg 6
• Patients ≥6 years: Refer to emergency department if ingestion ≥7.5 mg/kg or 300 mg (whichever is less) 6
• Symptom onset: Monitor for 6 hours post-ingestion; if no symptoms develop by 6 hours, emergency referral is not needed 6

Administration Precautions

• Intravenous administration: Must dilute 50 mg in 10 mL normal saline and inject slowly over 2 minutes to minimize adverse reactions 1
• Inspect solution: Visually inspect for particulate matter and discoloration before administration 1

Clinical Positioning

Dimenhydrinate is FDA-indicated for prevention and treatment of nausea, vomiting, or vertigo of motion sickness 1, but is commonly used off-label for other causes of nausea. In contemporary emergency department practice, dimenhydrinate is not listed among first-line agents (which include dopaminergic antagonists like haloperidol, metoclopramide, or prochlorperazine) 7, suggesting it may be most appropriate for motion sickness or as an adjunctive agent when first-line therapies are contraindicated or unavailable.