Pyridostigmin belongs as a drug to the group of indirect parasympathomimetics. It thus indirectly activates the acetylcholine activity on the receptors of the parasympathetic nervous system by inhibiting the enzyme acetylcholinesterase.
The active substance is a quaternary amine complex which is present in medicaments as bromide. Dissolved pyridostigmine bromide is a white, crystalline powder. It dissolves very well in water. The drug is administered as needed in the form of tablets.
Pyridostigmine bromide can not cross the blood-brain barrier because it is not lipophilic due to its salt-like structure. Its plasma half life is about 1.5 hours. After use, the drug is partially metabolized and excreted partly unchanged renal (via the urine).
Pyridostigmine indirectly acts by inhibiting the enzyme acetylcholinesterase. This enzyme is responsible for the degradation of the neurotransmitter acetylcholine in the synaptic cleft to acetate and choline.
The inhibition of acetylcholinesterase in turn causes an increase in the acetylcholine concentration at the motor end plate. The existing there acetylcholine receptors are cation channels, which stimulated by acetylcholine cation currents stimulate the muscles. This increases the tone (tension) of certain muscles, increasing the likelihood of muscle contraction. In general, the activity of the parasympathetic nervous system, which is responsible for the physical processes in the resting phase, is also increasing.
The parasympathetic nervous system controls muscle tone and metabolic processes including bowel and bladder function. In autoimmune myasthenia gravis, disorders of the receptors for acetylcholine occur, so that only a higher acetylcholine concentration can cause sufficient muscle contractions.
The bladder or intestinal muscles are stimulated. This property also makes pyridostigmine a good drug for treating paralysis of the bladder or bowel muscles. The increase in acetalcholine concentration also causes a suppression of antagonist muscle relaxants from the acetylcholine receptors, which are used as muscle relaxant drugs. If necessary, pyridostigmine is used to eliminate the effects of these drugs.
Pyridostigmine is mainly used to treat the disease Myasthenia gravis. Depending on the severity of the disease, the doctor must determine the individual dose of the drug.
The treatment begins with the sole administration of pyridostigmine. However, if there is no improvement, treatment may continue in combination with guanine. The drug is administered in the form of tablets. Due to the many possible side effects and the possibility of interaction with various other drugs, the treatment should always take place under medical supervision.
The use together with other parasympathomimetic agents leads to the enhancement of the effect. The effect of the muscle relaxant medication is removed. If necessary, pyridostigmine should be used in the event of overdose with muscle relaxants or other problems. Another application is the application in case of urinary retention or intestinal atony (intestinal paralysis). However, care must be taken to ensure that pyridostigmine is absolutely contraindicated in the case of a mechanical bowel obstruction or a mechanically induced bladder emptying disorder.
The stimulation of the bladder or intestinal musculature in this case can lead to serious complications. Prophylactically pyridostigmine was also used in the "Second Gulf War 1991" against poisoning by cholinesterase inhibitor-based chemical warfare agents.
The use of pyridostigmine, as with all medications, carries the risk of side effects that may occur but need not occur.
As the activity of the parasympathetic nervous system is increased, varying degrees of such symptoms result, such as diarrhea, vomiting, abdominal cramps, increased salivation, increased mucus formation in the bronchi, bradycardia, hypotension and adjustment disorders of the eye. As bronchoconstriction may also be restricted, it is contraindicated in patients with obstructive pulmonary disease.
The same applies to mechanical bowel and bladder closure. An overdose of the drug can lead to a weakening of the airway muscles due to a cholinergic crisis. Other side effects include increased sweating and increased urination. Pregnancy or breast-feeding should be avoided with pyridostigmine.