Usage
- Dimenhydrinate is primarily prescribed for the prevention and treatment of nausea, vomiting, and dizziness associated with motion sickness. It is also used off-label for vertigo associated with Meniere’s disease.
- Pharmacological Classification: Dimenhydrinate is classified as an antihistamine (H1 receptor antagonist), antiemetic, and anticholinergic agent.
- Mechanism of Action: Dimenhydrinate acts by blocking the effects of histamine in the brain, particularly in the vomiting center and vestibular system, thereby suppressing nausea, vomiting, and vertigo. Its anticholinergic properties also contribute to its efficacy against motion sickness.
Alternate Names
- Dimenhydrinate is also known as diphenhydramine 8-chlorotheophyllinate, which reflects its chemical composition as a combination of diphenhydramine and 8-chlorotheophylline.
- Brand Names: Dramamine, Gravol, Driminate, Travel-Eze, and others.
How It Works
- Pharmacodynamics: Dimenhydrinate exerts its effects by antagonizing H1 histamine receptors in the brain, inhibiting vestibular and reticular pathways involved in motion sickness. It also possesses anticholinergic activity, which contributes to its antiemetic properties.
- Pharmacokinetics: Dimenhydrinate is well-absorbed after oral administration, reaching peak plasma concentrations within 1-4 hours. It undergoes extensive hepatic metabolism, primarily by CYP2D6, and is excreted mainly in the urine.
- Mode of Action: Dimenhydrinate competitively binds to H1 receptors, preventing histamine from binding and triggering the cascade of events that lead to nausea and vomiting. The anticholinergic effects further inhibit vestibular stimulation.
- Elimination Pathways: Dimenhydrinate is primarily metabolized by the liver and excreted in the urine.
Dosage
Standard Dosage
Adults:
- Oral: 50-100 mg every 4-6 hours as needed.
- Intramuscular (IM): 50 mg every 4-6 hours as needed.
- Intravenous (IV): 50 mg (diluted in 10 ml of normal saline) administered slowly over 2 minutes, repeatable every 4-6 hours as needed.
- Maximum daily dose: 400 mg.
Children:
- Oral:
- 2-6 years: 12.5-25 mg every 6-8 hours as needed (maximum 75 mg/day).
- 6-12 years: 25-50 mg every 6-8 hours as needed (maximum 150 mg/day).
- IM: 1.25 mg/kg (maximum single dose 25 mg) every 4-6 hours, not to exceed 5mg/kg/day.
- Rectal: Refer to specific product guidelines as formulations and dosages vary.
- Pediatric Safety Considerations: Dimenhydrinate can cause paradoxical excitation in children. Close monitoring is advised. Use with caution in children under 2. Not recommended in neonates.
Special Cases:
- Elderly Patients: Start with a lower dose (25 mg) and titrate as needed.
- Patients with Renal Impairment: Use with caution. Dose adjustment may be needed in severe renal impairment.
- Patients with Hepatic Dysfunction: Use with caution. Dose adjustment may be required.
- Patients with Comorbid Conditions: Use with caution in patients with glaucoma, prostatic hyperplasia, asthma, cardiovascular disease, and seizure disorders.
Clinical Use Cases
- The dosages outlined in the standard dosage section are applicable in clinical settings such as intubation, surgical procedures, mechanical ventilation, ICU use, and emergency situations. Individual patient factors must be considered.
Dosage Adjustments
- Adjust dosage based on patient response and tolerance.
- Renal/hepatic impairment, metabolic disorders, and genetic polymorphisms affecting CYP2D6 may necessitate dose adjustments.
Side Effects
Common Side Effects
- Drowsiness, dizziness, dry mouth, blurred vision, constipation.
Rare but Serious Side Effects
- Allergic reactions (rash, itching, hives, swelling), difficulty breathing, hallucinations, seizures, irregular heartbeat.
Long-Term Effects
- Chronic anticholinergic use may be associated with an increased risk of cognitive decline in the elderly.
Adverse Drug Reactions (ADR)
- Severe allergic reactions (anaphylaxis), paradoxical excitation (especially in children), extrapyramidal symptoms, QT prolongation.
Contraindications
- Hypersensitivity to dimenhydrinate or diphenhydramine.
- Narrow-angle glaucoma, severe respiratory disease, urinary retention, prostatic hypertrophy.
- Newborns, especially premature infants.
Drug Interactions
- Alcohol, CNS depressants (benzodiazepines, opioids), anticholinergics (tricyclic antidepressants, MAOIs), other antihistamines: additive sedative effects.
- CYP2D6 inhibitors/inducers can alter dimenhydrinate metabolism.
- Avoid grapefruit juice as it may interact with dimenhydrinate metabolism.
Pregnancy and Breastfeeding
- Pregnancy Safety Category: B (Animal studies show no fetal harm, but adequate human studies are lacking.)
- Fetal Risks: While considered relatively safe, potential risks cannot be ruled out entirely.
- Breastfeeding: Small amounts are excreted in breast milk. Occasional use is generally considered safe, but large doses or prolonged use may affect the infant or milk supply.
Drug Profile Summary
- Mechanism of Action: H1 receptor antagonist, anticholinergic, and antiemetic.
- Side Effects: Drowsiness, dizziness, dry mouth, blurred vision, constipation. Rarely, allergic reactions, seizures.
- Contraindications: Hypersensitivity, narrow-angle glaucoma, severe respiratory disease, urinary retention, newborns.
- Drug Interactions: Alcohol, CNS depressants, anticholinergics, other antihistamines.
- Pregnancy & Breastfeeding: Generally safe in pregnancy; caution in breastfeeding, especially with large doses.
- Dosage: Adults: 50-100 mg q4-6h; children: dose based on age (see detailed section).
- Monitoring Parameters: Observe for adverse effects, especially drowsiness and paradoxical excitation in children. Monitor for signs of allergic reactions.
Popular Combinations
- Dimenhydrinate is sometimes combined with pyridoxine (vitamin B6) for morning sickness.
Precautions
- General Precautions: Assess for allergies, pre-existing conditions (especially glaucoma, respiratory issues, prostate problems), and concomitant medications.
- Specific Populations: Exercise caution in pregnant/breastfeeding women, children, and elderly.
- Lifestyle Considerations: Avoid alcohol and activities requiring alertness.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Dimenhydrinate?
A: Adults: 50-100 mg every 4-6 hours; Children: dose based on age (see detailed dosage section). Maximum daily dose 400 mg for adults and 5mg/kg for children.
Q2: Can Dimenhydrinate be used in children under 2?
A: Use with extreme caution and only under medical supervision in children under 2 years old. It is contraindicated in neonates and premature infants.
Q3: What are the most common side effects?
A: Drowsiness, dizziness, dry mouth, blurred vision, and constipation are the most common side effects.
Q4: Can Dimenhydrinate be used during pregnancy?
A: It is generally considered safe for use during pregnancy, but discuss it with your OB-GYN.
Q5: Does Dimenhydrinate interact with other medications?
A: Yes, it can interact with alcohol, CNS depressants, anticholinergics, and other antihistamines.
Q6: How should Dimenhydrinate be administered intravenously?
A: Dilute 50 mg in 10 ml normal saline and administer slowly over at least 2 minutes.
Q7: What should I do if a patient experiences an allergic reaction?
A: Discontinue the medication immediately and provide supportive care. In severe cases, administer epinephrine and other appropriate emergency measures.
A: While sometimes used off-label for vertigo associated with Meniere’s disease, its primary indication is motion sickness. Other medications might be more appropriate for other causes of vertigo.
Q9: Are there any long-term risks associated with Dimenhydrinate use?
A: Chronic anticholinergic use, including dimenhydrinate, has been linked to a higher risk of cognitive decline in the elderly.
