Absorption, Distribution and Excretion
The onset of action after oral administration is approximately 320 minutes… The duration of action after oral administration is generally slightly longer, and absorption is more stable than that of neostigmine, which are advantages. Plasma pyridostigmine concentrations were determined in two lactating women who received oral administration of 120–300 mg of pyridostigmine bromide daily. The drug was not detected in the plasma of the infants, and no adverse drug reactions were observed in the infants. Metabolism/Metabolites Pyridostigmine and its quaternary ammonium alcohol are the major metabolites found in urine after administration of this drug in humans. Biological Half-Life Following intravenous injection of pyridostigmine bromide (200 nmol/kg) in human subjects, the disposal half-life was 0.6–1.78 minutes, and the terminal half-life was 14.81–37.01 minutes. The clearance rate was 9.3-26.5 ml/min/kg, higher than the estimated value of glomerular filtration rate, and the volume of distribution was 246.5-833.9 ml/kg.

Effects During Pregnancy and Lactation
◉ Overview of Use During Lactation
Due to the low levels of pyridostigmine in breast milk, the amount ingested by infants is very small, resulting in low serum concentrations. Pyridostigmine is not expected to have any adverse effects on breastfed infants. Most mothers with myasthenia gravis are able to breastfeed successfully while receiving pyridostigmine treatment, but sometimes breastfeeding must be discontinued to avoid excessive maternal fatigue.
◉ Effects on Breastfed Infants
A woman with myasthenia gravis took 120 mg of pyridostigmine every 4 to 5 hours. Her breastfed infant (the extent of feeding was not specified) reported to be developing well and without cholinergic side effects.
Two infants whose mothers took pyridostigmine 3 and 5 mg/kg daily during pregnancy and lactation were exclusively breastfed. Both infants had normal weight gain and development, and no cholinergic side effects.
◉ Effects on Lactation and Breast Milk
As of the revision date, no published information was found regarding the use of pyridostigmine by lactating mothers. In animal studies, cholinergic drugs increase oxytocin release and have varying effects on serum prolactin levels. Prolactin levels in established lactating mothers may not affect their ability to breastfeed.
In a case series of 69 pregnancies in 65 women with myasthenia gravis over 27 years, 49 patients received pyridostigmine treatment during pregnancy and lactation. Lactation data were available for 33 patients, of whom 25 were successfully breastfed, but the number of mothers taking pyridostigmine was not provided. Breastfeeding is sometimes interrupted to avoid maternal fatigue.

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Interactions
Anticholinesterase drugs act on autonomic effector cells and the cortical and subcortical sites of the central nervous system, with receptors primarily of the muscarinic type, which are blocked by atropine. /Anticholinergic Drugs/
A case of methoxycarbazine potentially impairing the efficacy of pyridostigmine bromide in patients with myasthenia gravis has been reported.
In anesthetized patients, intravenous administration of 10 mg pyridostigmine bromide antagonized neuromuscular blockade induced by 0.29 mg/kg/hour of d-tubocurarine chloride. Adequate recovery of neuromuscular blockade should be assessed by the following indicators: recovery of muscle twitching amplitude to control levels, and recovery of sustained tetanic contractions (30 times/second) to pre-d-tubocurarine chloride levels.
In patients with renal failure, the duration of succinylcholine action was prolonged after administration of neostigmine and pyridostigmine.
Gamma-aminobutyric acid (GABA), as a supplement to pyridostigmine bromide, reduced the incidence of chicken embryo malformations.

Neuroscience.2013 Aug 29;246:391-6;Luminescence.2011 Nov-Dec;26(6):510-7.

Pyridostigmine bromide is a pyridine salt. Pyridostigmine is a drug approved by the U.S. Food and Drug Administration (FDA) under the brand name Mestinon for the treatment of myasthenia gravis; and under the brand name Regonol for reversing the effects of muscle relaxants. Additionally, pyridostigmine is approved for pretreatment of military personnel exposed to the chemical nerve agent soman. Currently, it is being investigated as an investigational drug for the treatment of HIV infection. As an investigational HIV drug, pyridostigmine belongs to the class of immunomodulatory agents. Immunomodulators are substances that can activate, enhance, or restore normal immune function. Researchers are currently investigating whether adding pyridostigmine to antiretroviral therapy (ART) can help increase CD4 counts in HIV-infected individuals. Pyridostigmine bromide is the bromide salt form of pyridostigmine, a quaternary ammonium carbamate derivative and an acetylcholinesterase inhibitor. Pyridostigmine bromide reversibly binds to the active site of acetylcholinesterase in the peripheral nervous system, thereby preventing the breakdown of acetylcholine. This leads to the accumulation of acetylcholine at cholinergic synapses and promotes the transmission of nerve impulses at the neuromuscular junction. The drug acts through muscarinic receptors, increasing the contraction of bronchial and intestinal smooth muscle and the secretion of exocrine glands, while simultaneously causing skeletal muscle paralysis through nicotinic receptors. Furthermore, pyridostigmine can also act as a reversible blocker, preventing organophosphates from binding to acetylcholinesterase receptors, thereby protecting the nervous system from neurotoxins such as soman. A cholinesterase inhibitor with a slightly longer duration of action than neostigmine. It is used to treat myasthenia gravis and reverse the effects of muscle relaxants. See also: Pyridostigmine (with the active moiety). Mechanism of Action…The pharmacological action of anticholinesterase drugs is primarily attributed to their inhibition of the hydrolysis of acetylcholine (ACH) by acetylcholinesterase (ACHE) at cholinergic transmission sites. Therefore, neurotransmitters accumulate, enhancing the effects of acetylcholine (ACH) released by cholinergic impulses or leaked from nerve endings.
After administration of pyridostigmine bromide to rats, the recovery of erythrocyte acetylcholinesterase activity was slow due to the covalent nature of the inhibitory effect. The logarithm of plasma pyridostigmine bromide concentration was linearly correlated with the increase in tibial anterior muscle twitching tone, due to the promoting effect of neuromuscular transmission.
Among 12 pyridostigmine analogues prepared by reacting 2-substituted 3-pyridinol with the desired carbamoyl chloride, 2-iodo-3-(dimethylcarbamoyloxy)pyridinemethyliodide was the most potent inhibitor of both acetylcholinesterase and butyrylcholinesterase activities. The stepwise inhibition curves of AChE and BuChE were compared and correlated with the ionic attraction and steric hindrance of the inhibitors.

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Therapeutic Use
Cholinesterase inhibitor; parasympathomimetic drug
A quaternary ammonium anticholinesterase drug…primarily used to treat myasthenia gravis.
...
Dosage: The equivalent parenteral dose of pyridostigmine is approximately 1/30th of the oral dose.
Pyridostigmine has a slower onset of action (13 minutes), slower than ethanocyanine chloride (3 minutes) or neostigmine (6-8 minutes), but a longer duration of action. Therefore, it is recommended for use in patients with renal insufficiency.
For more complete data on the therapeutic uses of pyridostigmine bromide (9 types), please visit the HSDB record page.

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Drug Warnings
Occasionally, bromide allergic reactions have occurred.
Maternal use usually compatible with breastfeeding: Pyridostigmine: Signs or symptoms reported in infants or effects on lactation: None. /Excerpt from Table 6/

C9H13BRN2O2

261.12

260.016

101-26-8

Pyridostigmine-d6 bromide;2375858-08-3;Pyridostigmine-d3 bromide

7550

White to off-white solid powder

0.9613 g/cm3 (20ºC)

88 (25 torr)

154 °C

1.48 (20ºC)

0

3

2

14

183

0

VNYBTNPBYXSMOO-UHFFFAOYSA-M

InChI=1S/C9H13N2O2.BrH/c1-10(2)9(12)13-8-5-4-6-11(3)7-8;/h4-7H,1-3H3;1H/q+1;/p-1

(1-methylpyridin-1-ium-3-yl) N,N-dimethylcarbamate;bromide

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment (e.g. under nitrogen), avoid exposure to moisture.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: ≥ 2.5 mg/mL (9.57 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (9.57 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (9.57 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 4: 100 mg/mL (382.97 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with ultrasonication.

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 (Please use freshly prepared in vivo formulations for optimal results.)