Medication used to preven and treat motion sickness

- Sedating antihistamines and hyoscine are licensed for use without prescription
for prophylaxis and treatment of motion sickness. They appear to be of more or
less equivalent efficacy
- They are effective for prevention, but use for treatment is often unsuccessful as
vomiting and gastric stasis prevent or substantially reduce their absorption




Hyoscine
- Hyoscine competitively inhibits the actions of acetylcholine at the muscarinic
receptors of autonomic effector sites innervated by parasympathetic nerves. It
has a central as well as a peripheral action, as it is lipid-soluble and crosses the
blood–brain barrier
- Hyoscine is relatively short-acting and has more pronounced antimuscarinic
side-effects than antihistamines


Sedating antihistamines
- The older (fi rst-generation) antihistamines which tend to cause sedation
have antimuscarinic side-effects similar to the actions of hyoscine. (Secondgeneration
antihistamines, which generally do not cause drowsiness, do not
exert antimuscarinic side-effects and are of no use for motion sickness.)
- Sedating antihistamines licensed for the treatment of motion sickness (all P
medicines) are:
– cinnarizine
– meclozine
– promethazine hydrochloride
– promethazine teoclate.


Side-effects
Hyoscine and antihistamines exhibit the same range of side effects. However,
side-effects tend to be more pronounced with hyoscine, and include:
– dry mouth
– blurred vision
– urinary retention
– constipation
– sedation (more marked with antihistamines).

Contra-indications
Both hyoscine and antihistamines should be avoided in patients suffering from
glaucoma or prostatic hypertrophy

Cautions
Both hyoscine and antihistamines are not recommended for use by pregnant
or breastfeeding women, and should be used with caution in the elderly and
patients with epilepsy or cardiac or cardiovascular disease.


Drug-drug interactions
Hyoscine and sedating antihistamines increase the effects of other drugs that
cause sedation or have antimuscarinic actions, including many antidepressants
and antipsychotic agents.
Alcohol should be avoided when taking medication against motion sickness.