Drug information

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Other Names
Mestinon, PDG, Regonol, pyridostigmine bromide
Drug Class
Immune Modulators
Molecular Formula

C9 H13 Br N2 O2

Registry Number
101-26-8 (CAS)
Chemical Name

3-hydroxy-1-methylpyridinium bromide dimethylcarbamate

Chemical Class
Phase of Development

Pyridostigmine is in Phase 2 development as an HIV treatment.

(Compound details obtained from PubChem,1 Treatment Action Group Pipeline Report 2021,2 and Current Neuropharmacology article3)

What is pyridostigmine?What is pyridostigmine?

What is pyridostigmine?

Pyridostigmine is a drug that has been approved by the U.S. Food and Drug Administration (FDA) to treat a condition called myasthenia gravis and to reverse the effects of muscle relaxants.4,5 In addition, pyridostigmine has been used in the military as a pretreatment for exposure to the chemical nerve agent Soman.6 It is also being studied as an investigational drug to treat HIV infection.2

As an investigational HIV drug, pyridostigmine belongs to a group of drugs called immune modulators.2 Immune modulators (also called immunomodulators) are substances that help to activate, boost, or restore normal immune function.

Researchers are currently studying whether pyridostigmine added to antiretroviral therapy (ART) can help a person with HIV increase their CD4 count.7

To learn how investigational drugs are tested during clinical trials, read the HIVinfo What is an Investigational HIV Drug? and HIV and AIDS Clinical Trials fact sheets.

Select clinical trials of pyridostigmineSelect clinical trials of pyridostigmine

Select clinical trials of pyridostigmine

Study Name: NCT00518154
Phase: 2
Status: This study has been completed.
Location: Mexico
Purpose: The purpose of this study was to evaluate whether adding pyridostigmine to ART could increase the CD4 count in individuals who had low CD4 counts despite having viral suppression on ART.8
Selected Study Results: Results published in Frontiers in Immunology (2017) found that the addition of pyridostigmine to ART led to a significant and long-lasting increase in circulating CD4 cells relative to baseline in participants who had incomplete immune reconstitution on ART.9 

Study Name: NCT03312244
Phase: 2
Status: See the ClinicalTrials.gov record for this study’s status.
Location: Mexico
Purpose: The purpose of this study is to evaluate whether adding pyridostigmine to ART can increase CD4 counts in individuals who have viral suppression on ART.7

For more details on the studies listed above, see the Health Professional version of this drug summary.

An additional Phase 1/2 study (NCT04353778) is evaluating whether pyridostigmine can reduce bacterial overgrowth in the small intestines and signs of inflammation in adults with HIV. This study is currently recruiting participants.10

What side effects might pyridostigmine cause?What side effects might pyridostigmine cause?

What side effects might pyridostigmine cause?

One goal of HIV research is to identify new drugs that have fewer side effects. In the NCT00518154 study discussed under the previous section, seven participants were enrolled to receive pyridostigmine in addition to ART. No side effects related to pyridostigmine were reported during the study.9

Because pyridostigmine is still being studied, information on possible side effects of the drug is not complete. As testing of pyridostigmine continues, additional information on possible side effects will be gathered.

Additional information on side effects that are known to be associated with pyridostigmine can be found in the FDA-approved Full Prescribing Information for Mestinon and pyridostigmine bromide.4,6 

Where can I get more information about clinical trials studying pyridostigmine?Where can I get more information about clinical trials studying pyridostigmine?

Where can I get more information about clinical trials studying pyridostigmine?

More information about pyridostigmine-related research studies is available from ClinicalTrials.gov. (The ClinicalTrials.gov search can be modified so that you can get results that better match your interests. To learn more about the ClinicalTrials.gov search features, please see How to Search.)

Some clinical trials may be looking for volunteer participants. Your health care provider can help you decide whether participating in a clinical trial is right for you. For more information, visit NIH Clinical Research Trials and You.



  1. National Center for Biotechnology Information. PubChem Compound Summary for CID 7550, Pyridostigmine bromide. https://pubchem.ncbi.nlm.nih.gov/compound/Pyridostigmine-bromide. Accessed March 13, 2023
  2. Jefferys R. Research toward a cure and immune-based therapies. Treatment Action Group Pipeline Report 2021. https://www.treatmentactiongroup.org/wp-content/uploads/2021/07/pipeline_2021_hiv_cures_final.pdf. Accessed July 20, 2022
  3. Čolović MB, Krstić DZ, Lazarević-Pašti TD, Bondžić AM, Vasić VM. Acetylcholinesterase inhibitors: pharmacology and toxicology. Curr Neuropharmacol. 2013;11(3):315-335. doi:10.2174/1570159X11311030006
  4. Bausch Health US, LLC. Mestinon: full prescribing information, December 2, 2020. DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=a851795e-b7a8-40c3-9922-5e79d3eb4d92. Accessed July 20, 2022
  5. Sandoz Inc. Regonol: full prescribing information, April 1, 2021. DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=208af931-a44e-43bf-a265-8e08534dc55f. Accessed July 20, 2022
  6. Surgeon General-Department of the Army (TSG-DA). Pyridostigmine bromide: full prescribing information, January 14, 2021. DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=0b296555-c32f-42db-b5f3-ea981a3dd2f8. Accessed July 20, 2022
  7. Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran. Study of the role of peripheral acetylcholinesterase inhibitor pyridostigmine as immunomodulators in a population of patients living with human immunodeficiency virus infection. In: ClinicalTrials.gov. Bethesda (MD): National Library of Medicine (US). Registered April 1, 2017. NLM Identifier: NCT03312244. https://clinicaltrials.gov/ct2/show/NCT03312244. Accessed July 20, 2022
  8. Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran. Pilot study of an ACh-E inhibitor upon immune activation markers in HIV-1 infected patients receiving highly active antiretroviral therapy (HAART) showing an incomplete immune response. In: ClinicalTrials.gov. Bethesda (MD): National Library of Medicine (US). Registered August 17, 2007. NLM Identifier: NCT00518154. https://clinicaltrials.gov/ct2/show/NCT00518154. Accessed July 20, 2022
  9. Valdés-Ferrer SI, Crispín JC, Belaunzarán-Zamudio PF, et al. Add-on pyridostigmine enhances CD4+ T-cell recovery in HIV-1-infected immunological non-responders: a proof-of-concept study. Front Immunol. 2017;8. doi:10.3389/fimmu.2017.01301 
  10. Icahn School of Medicine at Mount Sinai. Effects of vagal dysfunction on gastrointestinal and inflammatory pathways in HIV. In: ClinicalTrials.gov. Bethesda (MD): National Library of Medicine (US). Registered April 17, 2020. NLM Identifier: NCT04353778. https://clinicaltrials.gov/ct2/show/NCT04353778. Accessed July 20, 2022



Last Reviewed: July 20, 2022