Atropine and the other muscarinic receptor antagonists

Therapeutic uses of atropine and the other muscarinic receptor antagonists

Atropine and the other muscarinic receptor antagonists are indicated in various clinical conditions.

Antispasmodic

As antispasmodic it can be used to control gastrointestinal hypermotility and hypertonicity of the uterus , urinary bladder,  ureter, bile duct and bronchioles. But  in the bronchiolar spasm it is not as effective as adrenergic drugs.

Preanaesthetics

Used as an adjunct to general anaesthesia as it reduces the salivary and airway secretions.

However, in cattle its use may result in inappetance and rumen stasis. In addition to the reduction in secretions these drugs also block the vagal reflexes to the heart during anaesthesia. Scopolamine causes tranquility and amnesia because of its central actions.

With morphine, scopolamine produces analgesia and amnesia. Glycopyrrolate is preferred as a preanesthetic because of its less significant  effect on the heart.

Ophthalmology

Used to dilate the pupils and paralyze accommodation in the treatment of various inflammatory conditions of the eye and as an aid to ophthalmoscopic examination.

Atropine is no longer a drug of choice for producing mydriasis or cycloplegia as its effects are too long lasting. Homatropine is the drug of choice for producing mydriasis as it produces only weak cycloplegia.

Cyclopentolate and tropicamide were developed specifically for ophthalmic use and have rapid recovery times.

Antidote for anticholinesterase poisoning and over dosage 

Used as an antidote in the treatment of poisoning by  cholinestrase inhibitors like carbamates and organophosphorus compounds. 

Other uses

Acute rhinitis, hay fever, motion sickness, myasthenia gravis and common cold.

Toxicity of atropine

Interspecies variations are observed with atropine toxicity-

1. Herbivores are more resistant than carnivores.
2. Certain strains of rabbits are resistant to a diet of belladonna leaves, (as the liver contains the enzyme atropinase) although eating their meat may be toxic if eaten by dogs, cats or humans
3. Horses, cattle and goats are relatively resistant when given orally, but when administered parenterally, they are susceptible
4. Swine are susceptible to poisoning, usually from eating the deadly nightshade plant.
5. Signs of toxicity includes dry mouth, thirst, constipation, mydriasis, tachycardia, restlessness, delirium, ataxia, convulsions, respiratory depression and respiratory failure leads to death. When urine from the animal suspected of atropine poisoning is instilled in the eye of a cat, dilatation can be noticed

Treatment of atropine poisoning or atropa belladonna poisoning

• Symptoms of atropa belladonna poisoning–
  1. Hot as hare (atropine fever)
  2. Red as beetroot (atropine flush)
  3. Dry as bone
  4. Blind as bat
  5. Mad as hatter (atropine madness)

Severe poisoning of belladonna cause respiratory distress, Cardiovascular collapse, convulsions, coma and death.

• Treatment to follow in atropine poisoning–
  1. Hospitalization and gastric lavage
  2. Symptomatic treatment (for fever use antipyretic drugs and tepid sponging, for convulsion control use anti-convulsants
  3. Antidote- Physostigmine