The most common side effects of scopolamine use in anesthesia are related to its anticholinergic effects. These include dry mouth (xerostomia), blurred vision, dilated pupils (mydriasis), and photophobia. These symptoms are typically mild and can resolve quickly, especially after the removal of the transdermal patch. More severe side effects, such as flushed skin, tachycardia, agitation, and confusion, are rare but can occur if anticholinergic toxicity develops, especially in sensitive patients or those receiving higher doses of scopolamine.
Physostigmine, a cholinesterase inhibitor, can serve as an antidote in cases of scopolamine toxicity by increasing acetylcholine levels, which counteracts the effects of muscarinic receptor blockade. This is particularly useful in cases where anticholinergic toxicity leads to hallucinations, delirium, or severe agitation: the dose is 0.5 to 2 mg intravenously, given slowly (no faster than 1 mg per minute) and repeated if the delirium returns, since physostigmine wears off in 30 to 60 minutes while the patch keeps delivering drug. Removing the patch and washing the site is the first step.
Contraindications and Cautions in Anesthesia
Scopolamine is contraindicated in patients with angle-closure glaucoma, as its mydriatic effects can increase intraocular pressure and precipitate acute angle-closure glaucoma. It is also contraindicated in patients with allergies to belladonna alkaloids. Caution is advised in patients with myasthenia gravis: muscarinic blockers do not act at the nicotinic neuromuscular junction, so the concern is not weakness itself but the drug's interaction with the anticholinesterase therapy these patients take and their vulnerability to anticholinergic delirium. Caution is also advised in patients with urinary retention or gastrointestinal motility disorders, as scopolamine can worsen these conditions, and in patients with a history of seizures or psychosis, which the label lists as a specific warning.
Elderly patients are particularly susceptible to scopolamine’s central anticholinergic effects, such as confusion, delirium, and agitation. Monitoring these patients closely for signs of CNS adverse effects is essential during and after anesthesia.
Monitoring and Special Considerations
Patients using a scopolamine patch during anesthesia should be monitored for side effects, especially those related to CNS toxicity and delirium. Special caution is needed in pediatric, elderly, and psychiatric populations, where scopolamine can exacerbate underlying conditions or interact with psychiatric medications. Additionally, patients with hepatic or renal impairment should be monitored closely for adverse effects, as impaired drug metabolism can lead to drug accumulation and increased risk of toxicity.
Patients using a scopolamine patch should be advised to remove it before MRI, as the patch contains metal that can cause burns during imaging. Proper hand hygiene after applying the patch is important to avoid accidental eye contact, which can lead to blurred vision and dilated pupils.
Toxicity and Overdose
Scopolamine toxicity is relatively rare with the transdermal formulation, as the extended-release nature of the patch prevents large fluctuations in drug levels. However, toxicity may still occur, particularly with misuse or accidental ingestion of multiple patches. Symptoms of overdose include tachycardia, hallucinations, hyperthermia, and dry membranes. In severe cases, physostigmine can be administered as a reversal agent to counteract the anticholinergic effects of scopolamine. A separate problem is withdrawal: when a patch has been worn for several days, its removal can be followed by dizziness, nausea, vomiting, headache, and disturbed balance beginning 24 hours or more later, which should not be mistaken for a new PONV episode or a neurologic event.
