(Anti)cholinergic drugs in GI

(Anti)cholinergic drugs in GI

The neurotransmitter acetylcholine directly stimulates its muscarinic M3 receptor on smooth muscle cells in the GI tract. It is important to note that acetylcholine and the muscarinic receptors are the target of many different kinds of drugs. Therefore clinicians should be aware that GI side effects are very common with drugs influencing the cholinergic system.

Drugs with cholinergic activity:

  • Pilocarpine is a direct muscarinic agonist used primarily as eye drops for the treatment of glaucoma. Systemic preparations can be used to treat Sjögren's syndrome.
  • Cholinesterase inhibitors such as neostigmine are considered indirect acting as they inhibit the breakdown of released acetylcholine in the synapse, prolonging its exposure to the M3 receptor.
  • Both types of drugs enhance acetylcholine stimulation and cause muscarinic side effects (GI hypermotility: nausea, vomiting, diarrhoea, cramps).

Drugs with anticholinergic activity:

  • Scopolamine is an muscarinic receptor antagonist indicated for relaxation of the gastrointestinal musculature and prevention of motion sickness.
  • Other anticholinergics are used in the treatment of bronchoconstriction, mucus hypersecretion, pseudoparkinsonism, and acute dystonia.
  • All these agents are capable of causing constipation, dry mouth, and abdominal pain.

Scopolamine is a strong anticholinergic drug. What pharmacological actions would you expect it to have?