Antispasmodic Agent

Antispasmodic agents are drugs that antagonize the effect of ACh and inhibit parasympathetic activities leading to: GI smooth muscle relaxation & Reduced gastric acid secretion

They are also called Anticholinergics or Antimuscarinics since they antagonize the effect of ACh by blocking the muscarinics receptors.

A. Atropine and Related Alkaloids

Atropine (hyoscyamine, Belladonna) Related alkaloids (Hyoscine)

Plant alkaloids with similar activities

Lipid soluble and can penetrate the blood-brain barrier

Clinical Uses

1. GI hyper motility

2. To dilate pupil for eye examination

3. Motion sickness

4. Anaesthetic premedication

5. Parkinson’s disease

6. Management of asthma

7. Urinary frequency (incontinence)

Side Effects

CNS effect: Excitation, confusion, anti-emetic and anti-Parkinsonian effect

Common Side Effects: Thirst, arrhythmias, palpitation, constipation, flushing, pupilary dilatation, relaxation of gut, bronchial, biliary tract and bladder smooth, inhibition of gastric acid and respiratory secretions

B. Synthetic Antimuscarinics

Synthetic Drugs with action similar activities to atropine but have fewer side effects

Clinical Uses

They are widely used for hypermotility and hyperacidity of the of GI tract

1. Gut, Biliary tract and bladder

2. Excessive gastric acid secretion

3. Ulcerative colitis, peptic ulcer

4. Adjunctive treatment for non-ulcer dyspepsia

Tertiary amines

Name: Dicyclomine HCI

Less marked antimuscarinics action than atropine

Some direct antispasmodic action on smooth muscle

Side effects: Not recommended for infant under 6 months of age

Quaternary ammonium compounds

1. Represent a number of drugs

2. Less lipid-soluble than atropine

3. Less likely to cross the blood brain barrier

4. Widely used

Side effects:

Anti-cholinergic effect: Dry month, blurred vision, hesitant micturition and constipation

The elderly are particularly susceptible

Contraindicated in patients with glaucoma and urinary retention

Name: Hyoscine butylbromide (Buscopan, Dhacopan)

Recommended for GI spasm

Useful in endoscopy

Name: Scopolamine methylbromide (Holopon), Oxyphencyclimine HCI (Daricon), Pipenzolate bromide, Propantheline bromide, Robinul, Cospanon

M1-selective antimuscarinic

Name: Pirenzepine (Bisvanil)

1. Inhibits gastric acid and pepsin secretions

2. Useful in gastric and duodenal ulcers

Side effects: fewer, agranulocytosis and thrombocytopenia may occur

C. Other Drugs Altering GI Motility

Clinical Uses

1. Direct relaxants of intestinal smooth muscle

2. May relieve pain in the irritable bowel syndrome and GI spasm

3. No serious adverse effects but should be avoided in paralytic ileus (distension, vomiting)

Name: Averine citrate (Spasmonal)

Antispasmodic activity similar to Buscopan with fewer cholinergic side effects

Name: Piper mint oil

Produces local antispasmodic effect on the gut wall

Name: Mebeverine HCI (Duspatalin)

The antispasmodic action is not CNS medicated or cholinergic adverse effects are few

Relieves spasm without affecting gut motility

Can be used for patient with Benign Prostatic Hyperplasia (BPH) and glaucoma