From the Guidelines
Scopolamine patches work by blocking muscarinic acetylcholine receptors in the central nervous system, particularly in the vestibular nuclei and the chemoreceptor trigger zone (CTZ) in the brain, to prevent nausea and vomiting. The mechanism of action involves the blocking of acetylcholine from binding to M1 receptors in the vestibular apparatus and vomiting center, which reduces the sensitivity to motion and disrupts the pathway that would normally lead to nausea 1.
Key Points
- The patch delivers a steady, controlled release of scopolamine through the skin (transdermally), providing continuous protection against nausea for up to 72 hours.
- This transdermal delivery system allows the medication to bypass the digestive system, maintaining consistent blood levels and reducing gastrointestinal side effects.
- The patch is typically placed behind the ear because this area has good blood supply and thin skin, allowing for optimal absorption.
- Common side effects include dry mouth, drowsiness, and blurred vision, which occur due to the anticholinergic properties of scopolamine affecting other muscarinic receptors throughout the body.
Clinical Evidence
Studies have shown that scopolamine is effective in reducing postoperative nausea and vomiting 1, and it is often used in combination with other antiemetic agents to enhance its effectiveness 1. The use of scopolamine patches has been recommended for preventing nausea and vomiting in patients undergoing chemotherapy 1 and for managing breakthrough emesis 1.
Recommendations
The use of scopolamine patches is recommended for preventing nausea and vomiting, particularly in patients who are at high risk of developing these symptoms. However, it is essential to consider the potential side effects and interactions with other medications when using scopolamine patches. As with any medication, the benefits and risks should be carefully weighed, and patients should be closely monitored for any adverse effects.
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 of the scopolamine patch for nausea is through its anticholinergic effects, blocking cholinergic transmission in the central nervous system (CNS), specifically from the vestibular nuclei to higher centers in the CNS and from the reticular formation to the vomiting center 2. This action is believed to contribute to its effectiveness in preventing nausea. Key aspects of its mechanism include:
- Competitive inhibition at postganglionic muscarinic receptor sites
- Action on smooth muscles that respond to acetylcholine
- Blockage of cholinergic transmission in the CNS
From the Research
Mechanism of Action of Scopolamine Patch for Nausea
The scopolamine patch is a transdermal system that delivers 1.5 mg of scopolamine gradually over 72 hours, following an initial bolus 3. The mechanism of action of scopolamine in preventing nausea and vomiting is based on its role as a selective competitive antagonist of muscarinic cholinergic receptors 3.
Key Findings
- Low serum concentrations of scopolamine produce an antiemetic effect 3.
- Transdermal scopolamine is effective in preventing postoperative nausea and vomiting (PONV) versus placebo, with a significantly reduced risk for postoperative nausea, vomiting, and PONV in the first 24 hours after the start of anesthesia 3, 4.
- The use of scopolamine versus placebo in preventing motion sickness has been shown to be effective, with scopolamine being more effective than placebo in the prevention of symptoms 5.
- Transdermal scopolamine can be used in combination with other prophylactic treatments, such as intravenous ondansetron, to reduce the incidence and severity of PONV in high-risk patients 6.