Hyoscyamine (Scopolamine) for Motion Sickness
Transdermal scopolamine is the most effective single agent for preventing motion sickness and should be applied 4-16 hours before anticipated motion exposure for optimal effectiveness. 1
Mechanism of Action and Formulation
- Scopolamine acts as a competitive inhibitor of muscarinic acetylcholine receptors, blocking cholinergic transmission from vestibular nuclei to higher centers in the CNS and from the reticular formation to the vomiting center 1
- Transdermal scopolamine is FDA-approved for prevention of nausea and vomiting associated with motion sickness 1
- The transdermal system delivers approximately 1 mg of scopolamine over 3 days at a rate of about 5 μg/hour 1, 2
Administration Guidelines
- Apply the transdermal patch behind the ear on hairless skin 4-16 hours before anticipated motion exposure 1
- Clinical studies show a 75% reduction in motion-induced nausea and vomiting when applied within this timeframe 1
- Important timing consideration: The onset of benefit with transdermal scopolamine patches is approximately 12 hours, making it inappropriate for immediate symptom relief 3
- For immediate relief, subcutaneous injection of scopolamine can be administered when the patch is applied 3
Efficacy
- Transdermal scopolamine is significantly superior to placebo in preventing motion sickness 4, 5
- Studies show it is equivalent in efficacy to oral antihistamines like meclizine (meclozine) and dimenhydrinate for motion sickness prevention 6, 4
- Plasma concentrations reach peak levels (average 87 pg/mL) within 24 hours of application and maintain steady state for 72 hours 1, 2
Side Effects and Precautions
- Common side effects include dry mouth, drowsiness, and blurred vision due to reduced visual accommodation 1, 7
- Central nervous system effects may include reduced memory for new information, impaired attention, and decreased alertness 7
- Glycopyrrolate may be preferred over scopolamine in patients at risk for delirium, as it doesn't cross the blood-brain barrier effectively 3
- Significant individual variation in response to transdermal scopolamine has been reported, both between individuals and between different patch applications on the same individual 2, 7
Special Considerations
- After removal of the patch, plasma concentrations decline with a half-life of 9.5 hours 1
- For patients with acute vertigo, transdermal scopolamine and oral meclizine show similar efficacy 6
- Scopolamine should be used cautiously in pregnant women as it readily crosses the placenta 2
- Benzodiazepines can be considered as an alternative when other options have failed, but their beneficial effect on motion symptoms is small 3