Mr. K is prone to motion sickness, and asks if he can take over-the-counter dimenhydrinate tablets for long car rides. He reports that dimenhydrinate has worked well for him in the past without triggering manic episodes, and he did not anticipate needing to take it very often.
What would you tell Mr. K about dimenhydrinate for motion sickness during car rides?
a) Mr. K should not take dimenhydrinate to prevent motion sickness because he experienced a manic episode triggered by a scopolamine patch
b) Mr. K can use dimenhydrinate as much as he wants to prevent motion sickness because it poses no risk of mania
c) Mr. K can use dimenhydrinate with caution and sparingly on a trial basis, as long as he is taking his mood stabilizer
FOLLOW UP Cautious use
The psychiatrist advised Mr. K to take dimenhydrinate cautiously when needed for long car rides. The psychiatrist feels this is safe because Mr. K is taking a mood stabilizer (lithium). Also, although dimenhydrinate has anticholinergic properties, occasional use is thought to pose less risk of triggering mania than the constant anticholinergic exposure over several days with a scopolamine patch. (The scopolamine patch contains 1.5 mg of the drug delivered over 3 days [ie, 0.5 mg/d]. In trials of IV scopolamine for depression, the dosage was 0.4 mcg/kg/d administered over 3 consecutive days.15-17 For an adult weighing 70 kg, this would be equivalent to 0.24 mg/d. Therefore, using a scopolamine patch over 3 days would appear to deliver a robust antidepressant-level dosage, even taking into account possible lower bioavailability with transdermal administration compared with IV infusion.)
The psychiatrist concludes that sporadic use of dimenhydrinate tablets for motion sickness during occasional long car rides poses less of a risk for Mr. K of triggering mania than repeat use of a scopolamine patch.
The author’s observations
Mr. K’s case is notable for several reasons:
- Novelty. This might be the first report of scopolamine-induced mania in the literature. In clinical trials by Furey and Drevets,15 Drevets and Furey,16 and Ellis et al,17 no study participants who received scopolamine infusion developed mania or hypomania. Although it is possible that Mr. K’s manic episode could have occurred spontaneously and was coincidental to his scopolamine use, there are valid reasons why scopolamine could trigger mania in a vulnerable person.
- Biochemical insight. The case underscores the role of the muscarinic cholinergic system in regulating mood.10
- Rational medical care. Sensible clinical decision-making was needed when Mr. K asked about using dimenhydrinate for motion sickness during car rides. Although there might not be definitively correct answers for questions that arose during Mr. K’s care (in the absence of research literature), theoretical understanding of the antidepressant effects of anticholinergic medications helped inform the psychiatrist’s responses to Mr. K and his wife.