Dimenhydrinate
Dimenhydrinate
Brand names:Dramamine, Gravol
A first-generation H1 antihistamine combined with 8-chlorotheophylline, used primarily for motion sickness and vertigo. The diphenhydramine component provides central anticholinergic and antiemetic effects; the theophylline component was added historically to offset sedation but has minimal practical impact. Sedation is significant and limits operational use - meclizine is preferred when the operator must remain functional.
Pharmacology and Actions
Dimenhydrinate is a salt formulation of diphenhydramine and 8-chlorotheophylline. The antiemetic and antivertigo effects come primarily from the diphenhydramine component's anticholinergic activity at central vestibular and chemoreceptor trigger zone pathways. The 8-chlorotheophylline component is a mild stimulant intended to reduce sedation, but the clinical effect is minimal and sedation remains the dominant operational concern.
Indications
- Prevention and treatment of motion sickness
- Vertigo from Meniere disease or labyrinthitis
- Nausea associated with vestibular disorders
- Mild allergic reactions (less commonly used for this purpose)
Absolute Contraindications
- Known hypersensitivity to dimenhydrinate or diphenhydramine
- Acute asthma exacerbation
- Neonates
Precautions and Side Effects
Sedation is the dominant operational issue and the reason for non-mission-capable classification. Anticholinergic effects: dry mouth, blurred vision, urinary retention, constipation. CNS: dizziness, paradoxical excitation (especially in children and elderly), confusion. Cardiac: tachycardia, palpitations. Drug interactions: additive sedation with alcohol, opioids, benzodiazepines, and other CNS depressants; additive anticholinergic effects with tricyclic antidepressants, antipsychotics, and other antihistamines; the theophylline component may interact with adenosine, lithium, and beta-blockers. Half-life 8 hours (diphenhydramine component). Pregnancy Category B (commonly used for hyperemesis and motion sickness in pregnancy). Small amounts in breast milk; may reduce milk supply. Avoid in elderly due to high anticholinergic burden, falls risk, and cognitive impairment. Cautious use in narrow-angle glaucoma, prostatic hyperplasia, bladder neck obstruction, and pyloroduodenal obstruction. 50 mg dimenhydrinate is approximately equivalent to 25 mg diphenhydramine.
Adult Dosing
Pediatric Dosing
Children 2 to 6 years: 12.5 to 25 mg PO every 6 to 8 hours; max 75 mg per 24 hours. Children 6 to 12 years: 25 to 50 mg PO every 6 to 8 hours; max 150 mg per 24 hours. Children over 12 years: adult dosing.
Pharmacokinetics
Peak Effect: 1 to 2 hours.
Duration: 4 to 6 hours.
Storage and Handling
Store at room temperature. Protect from light. Stable in operational environments. Tablets and IM/IV preparations are robust.
Reconstitution:
Injectable available as 50 mg/mL. For IV use, dilute in 10 mL of compatible IV fluid (typically normal saline) and administer over at least 2 minutes.
TCCC and TECC Role
Dimenhydrinate is not in the TCCC core formulary. It appears in tactical EMS supplemental formularies for motion sickness prophylaxis during boat operations, rotary-wing insertion, and other vestibular-challenging environments. Classified as non-mission-capable on TEMS formularies due to sedation - the operator should not be on duty after a dose. Operational use is typically prophylactic for non-operators during transport, or for an operator who is being removed from operational status anyway.
Motion sickness is a real operational problem on water and during rotary-wing operations. Dimenhydrinate works, but so does meclizine with less sedation and longer duration of action. For operators who must remain functional, scopolamine patch (applied 4 hours before exposure) is the preferred motion sickness prophylactic - it provides longer protection with less sedation. Dimenhydrinate is more appropriate for casualty transport (passenger getting sick during evac) or for someone who is being put down for rest after a long operation.
Using dimenhydrinate as a routine antiemetic instead of ondansetron. The sedation is significant and the operational impact is greater than 5-HT3 antagonist nausea control. The other mistake is reaching for dimenhydrinate when the indication is actually vertigo plus nausea - meclizine is the better choice for sustained vestibular suppression.
This drug profile is provided as educational reference material for trained medical providers. It is not medical advice, not a substitute for formal training, and not a substitute for current published guidelines or medical direction.
Drug administration is governed by your scope of practice, agency standing orders, medical director protocols, and applicable state and federal regulations. Controlled substances are subject to additional handling, accountability, and documentation requirements per DEA and state law. Always verify dosing, indications, contraindications, and route of administration against current published guidelines and your local protocols before administration.
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Drug information evolves. Last reviewed dates and source citations are provided for each entry. Confirm currency against the cited source before clinical use.
Penn Tactical Solutions publishes this reference for educational purposes. PTS does not provide medical direction and does not assume responsibility for clinical decisions made in the field. Clinical responsibility rests with the administering provider, their medical director, and their agency.
Educational reference for trained medical providers. Not medical advice. Not a substitute for formal training, current published guidelines, or medical direction. Drug administration is governed by your scope of practice, agency standing orders, medical director protocols, and applicable state and federal regulations. Controlled substances require additional storage, accountability, and documentation per DEA and state law.
In a medical emergency, call 911. This reference is not a substitute for emergency medical services.
Verify dosing, indications, and contraindications against current published guidelines and your local protocols before administration. Confirm content currency against the source citation. Penn Tactical Solutions does not provide medical direction. Clinical responsibility rests with the administering provider, their medical director, and their agency.
Dimenhydrinate
| IV/IO | 50 mg IV every 4 hours as needed. Rarely used IV in EMS settings. (15 to 30 minutes) |
| IM | 50 mg IM every 4 hours as needed. Useful for prophylaxis when oral route is impractical (rotary-wing transport, water operations). (15 to 30 minutes) |
| IN | None (None) |
| PO | 50 to 100 mg PO every 4 to 6 hours as needed. Maximum 400 mg per 24 hours. For prophylaxis, give first dose 30 to 60 minutes before exposure. (30 minutes) |