Unithiol
Chelating agents
Chelating agents
A water-soluble dithiol chelator (DMPS) used for arsenic and mercury poisoning; a less toxic relative of dimercaprol.
Also called: DMPS, sodium 2,3-dimercaptopropane-1-sulfonate
Quick facts
- Group
- Chelating agents
- Target
- Arsenic and mercury ions in blood and tissues
- Used for
- Severe acute arsenic poisoning · Mercury poisoning
- Key effects
- Loss of zinc and copper
- Monitor
- Urine metal levels to judge response · Kidney function
No doses: the clinician sets them by the current guideline.
Mechanism of action
Unithiol carries two neighbouring thiol (-SH) groups, the same metal-gripping design as dimercaprol, plus a charged sulfonate group that makes it water-soluble. The thiols bind arsenic and mercury more tightly than the sulfhydryl groups of the body's enzymes, forming a stable complex that the kidneys excrete. Being water-soluble, it is less toxic than dimercaprol and can be given intravenously or by mouth. Chelation helps most when it starts within hours of absorption.
- Arsenic or mercury binds and blocks thiol enzymes
- Unithiol's two thiols grip the metal more tightly
- A water-soluble complex forms
- The kidneys excrete the metal
Indications
- Severe acute arsenic poisoning, under the guidance of a toxicology expert Arsenic poisoning →
- Mercury poisoning Mercury poisoning →
Adverse effects
- Loss of zinc and copper, which it also binds
Contraindications
- Known allergy to unithiol
- Not used to reverse established arsenic neuropathy, which chelation does not improve
Key interactions
- Dimercaprol (BAL)
- Unithiol is its water-soluble, less toxic relative and has largely replaced it for arsenic
What is monitored
- Urine metal levels to judge response and the end of treatment
- Kidney function, since the complex leaves through the kidneys
- Zinc and copper status during longer courses
Administration and safety
- Used only after a poison centre or clinical toxicologist has been consulted
- Often obtained through special-access programmes, so hospitals plan their supply
- Started as early as possible after acute exposure, when chelation helps most
Pregnancy and breastfeeding
Information on use in pregnancy is very limited; in serious poisoning the decision rests with toxicology specialists.
Nursing care
- Take a clear exposure history: which metal, how, and when
- Collect urine samples as instructed, ideally before chelation starts
- Watch fluid balance and urine output
- Remove the patient from the source of exposure; chelation does not replace this
Pharmacokinetics
- Absorption
- Given intravenously in acute poisoning; also absorbed by mouth
- Elimination
- Mainly by the kidneys, together with the bound metal
Test yourself
Think of the answer, then tap the question to see it.
Which two metals is unithiol mainly used for?
Arsenic and mercury.
What makes unithiol less toxic than dimercaprol?
Its sulfonate group makes it water-soluble, so it stays in body water and leaves through the kidneys.
Why does early treatment matter in acute arsenic poisoning?
Chelation helps most within hours of absorption; its benefit falls as time passes.
Connections
← Back to the class: Chelating agents
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Arsenic Toxicity: How Should Patients Overexposed to Arsenic Be Treated and Managed? | Environmental Medicine | ATSDR (Agency for Toxic Substances and Disease Registry (CDC), 2026); Chelating agents (excluding Deferoxamine) (Santé Québec Capitale-Nationale (Canadian antidote guide), 2022).
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Representative model, for educational purposes only.