Physostigmine

Physostigmine [fi-zoe-STIG-meen] is a nitrogenous carbamic acid ester found naturally in plants and is a tertiary amine. It is a substrate for acetylcholinesterase, and it forms a relatively stable carbamoylated intermediate with the enzyme, which then becomes reversibly inactivated. The result is potentiation of cholinergic activity throughout the body.

1. Actions: Physostigmine has a wide range of effects as a result of its action, and not only the muscarinic and nicotinic sites of the autonomic nervous system but also the nicotinic receptors of the neuromuscular junction are stimulated. Its duration of action is about 2 to 4 hours, and it is considered to be an intermediate-acting agent. Physostigmine can enter and stimulate the cholinergic sites in the CNS. 

2. Therapeutic uses: The drug increases intestinal and bladder motility, which serve as its therapeutic action in atony of either organ. Placed topically in the eye, it produces miosis and spasm of accommodation, as well as a lowering of intraocular pressure. It is used to treat glaucoma, but pilocarpine is more effective. Physostigmine is also used in the treatment of overdoses of drugs with anticholinergic actions, such as atropine, phenothiazines, and tricyclic antidepressants.

 3. Adverse effects: The effects of physostigmine on the CNS may lead to convulsions when high doses are used. Bradycardia and a fall in cardiac output may also occur. Inhibition of acetylcholinesterase at the skeletal neuromuscular junction causes the accumulation of acetylcholine and, ultimately, results in paralysis of skeletal muscle. However, these effects are rarely seen with therapeutic doses


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