Physostigmine works by inhibiting the action of the neurotransmitter acetylcholine at muscarinic cholinoreceptors. This results in a variety of effects, including:
* Miosis: Physostigmine causes the pupil to constrict by stimulating the sphincter muscle of the iris.
* Ciliary muscle contraction: Physostigmine also causes the ciliary muscle to contract, which results in accommodation (the ability to focus on near objects).
* Increased salivation and lacrimation: Physostigmine stimulates the salivary and lacrimal glands, which results in increased saliva and tear production.
* Slowing of the heart rate: Physostigmine can slow the heart rate by blocking the muscarinic cholinoreceptors in the heart.
* Increased bronchial secretions: Physostigmine can increase bronchial secretions by stimulating the muscarinic cholinoreceptors in the lungs.
Physostigmine is available in several different formulations, including eye drops, tablets, and injections. The most common side effects of physostigmine include blurred vision, headache, nausea, and vomiting. Serious side effects, such as respiratory depression and cardiac arrhythmias, can also occur.
Physostigmine is a potent medication that should be used only under the supervision of a doctor.