From the Guidelines
Scopolamine patches treat nausea by blocking muscarinic acetylcholine receptors in the central nervous system, particularly in the vestibular nuclei and chemoreceptor trigger zone. The medication is an anticholinergic agent that crosses the blood-brain barrier and prevents acetylcholine from binding to these receptors, which inhibits the neural pathways involved in triggering nausea and vomiting. According to the study 1, scopolamine is used off-label in gastroparesis despite lack of supporting clinical studies, and its dose is 1.5 mg patch every 3 days. The transdermal patch delivers a steady dose of scopolamine through the skin and into the bloodstream, providing continuous protection against motion sickness and postoperative nausea. This delivery method helps maintain consistent drug levels while avoiding first-pass metabolism in the liver. Scopolamine is particularly effective for motion sickness and postoperative nausea because it targets the vestibular system's contribution to nausea rather than just the gastrointestinal tract. Some key points to consider when using scopolamine patches include:
- The dose of scopolamine patch is 1.5 mg every 3 days, as indicated in the study 1
- Side effects can include dry mouth, drowsiness, blurred vision, and dizziness due to its anticholinergic properties affecting other body systems beyond those involved in nausea control. It's also worth noting that, as mentioned in the study 1, other medications such as ondansetron, granisetron, and metoclopramide are also available for treating nausea and vomiting, but scopolamine patches have a unique mechanism of action that makes them effective for certain types of nausea.
From the FDA Drug Label
Scopolamine, a belladonna alkaloid, is an anticholinergic. Scopolamine acts: i) as a competitive inhibitor at postganglionic muscarinic receptor sites of the parasympathetic nervous system, and ii) on smooth muscles that respond to acetylcholine but lack cholinergic innervation It has been suggested that scopolamine acts in the central nervous system (CNS) by blocking cholinergic transmission from the vestibular nuclei to higher centers in the CNS and from the reticular formation to the vomiting center
The mechanism of action for scopolamine patch in treating nausea is through its anticholinergic properties, acting as a competitive inhibitor at postganglionic muscarinic receptor sites of the parasympathetic nervous system. It is also suggested to block cholinergic transmission in the central nervous system (CNS), specifically from the vestibular nuclei to higher centers and from the reticular formation to the vomiting center 2. Key points of its mechanism include:
- Competitive inhibition at muscarinic receptor sites
- Blockage of cholinergic transmission in the CNS
- Effects on smooth muscles that respond to acetylcholine The scopolamine patch is designed to deliver approximately 1 mg of scopolamine to the systemic circulation over 3 days, providing a continuous release of the medication to help manage nausea 2.
From the Research
Mechanism of Action of Scopolamine Patch
The scopolamine patch is an antiemetic medication used to treat nausea, particularly postoperative nausea and vomiting. The mechanism of action of scopolamine involves its ability to block muscarinic acetylcholine receptors, which are involved in the transmission of nerve impulses in the brain and other parts of the body.
- Scopolamine is a non-selective muscarinic acetylcholine receptor (mAchR) antagonist, which means it blocks all types of muscarinic receptors, including M1, M2, M3, M4, and M5 subtypes 3.
- The M1 subtype of muscarinic receptors is thought to be involved in the antidepressant effects of scopolamine, and the administration of a selective M1-AChR antagonist has been shown to produce an antidepressant response similar to scopolamine 3.
- The scopolamine patch works by delivering a continuous dose of scopolamine through the skin and into the bloodstream, where it can bind to muscarinic receptors in the brain and other parts of the body.
Anticholinergic Effects
Scopolamine has anticholinergic effects, which can include:
- Bradycardia (slow heart rate)
- Dry mouth
- Dizziness
- Visual disturbances
- Delirium
- Urinary retention
These effects are more common in certain populations, such as the elderly, and can be severe enough to require medical attention 4, 5.
Clinical Use
The scopolamine patch is typically used to prevent postoperative nausea and vomiting, but its use has been associated with an increased risk of in-hospital adverse events, particularly in older patients 5. The patch may be more suitable for use in ambulatory patients, and clinicians should carefully assess the risks and benefits of using scopolamine in different patient populations.