How does Dimercaprol restore enzyme function?

The drug acts as a sulfhydryl (-SH) group donor. It binds the cardiac glycoside molecule via disulfide bridges, liberating the intrinsic thiol groups of $Na^+,K^+$-ATPase.

How do you calculate the dose of 5% Unithiol solution?

Dosage is calculated strictly by body weight: 1 mL of the 5% solution is required for every 10 kg of weight. It can be administered subcutaneously, intramuscularly, or intravenously.

Why is magnesium important alongside Unithiol when treating glycoside toxicity?

$Mg^{2+}$ ions are required activators of $Na^+,K^+$-ATPase. After Dimercaprol frees the enzyme from the glycoside, magnesium ensures active transport of potassium ions into the cardiomyocyte.

Can Dimercaprol be used to treat AV block caused by glycoside poisoning?

While the drug addresses the root cause by binding the glycoside, Atropine—which blocks $M_2$ receptors—is the drug of choice for the emergency correction of conduction disorders like AV block.

Dimercaprol & Unithiol: Mechanism, Uses and Dosing

Dimercaprol (Unithiol)

Unithiolum

For medical students2 min readUpdated 2026-10-10

Dimercaprol (Unithiolum) is an antidote, chelating agent, and sorbent used in clinical practice as a specific sulfhydryl group donor to treat severe complications caused by cardiac glycoside therapy. Its primary mechanism involves the reactivation of cellular enzymes by binding to toxin molecules.

Pharmacological GroupAntidotes, chelating agents, sorbents.

Mechanism-SH group donor, $Na^+,K^+$-ATPase reactivator.

IndicationTreatment of complications from cardiac glycoside therapy.

FormulationsPowder; 5% solution in 5 mL ampoules.

Routes of AdministrationSubcutaneous, intramuscular, and intravenous (1 mL of 5% solution per 10 kg).

Mechanism of Action: Molecular Level

Dimercaprol (Unithiolum) acts as a specific antidote and serves as an active donor of sulfhydryl (thiol, -SH) groups. Its mechanism is directly tied to the pathogenesis of cardiac glycoside intoxication.

The toxic effect of cardiac glycosides stems from their tight binding to the $Na^+,K^+$-ATPase enzyme in the cardiomyocyte membrane. When administered, Dimercaprol enters a direct chemical reaction with the cardiac glycoside molecule. Because it possesses free thiol groups, the antidote forms strong disulfide bridges with the toxin. Consequently, the glycoside molecule dissociates from the enzyme, liberating the essential thiol groups of $Na^+,K^+$-ATPase required for normal enzymatic function.

Pharmacological Effects and Indications

The key pharmacological effect is the full restoration of $Na^+,K^+$-ATPase transport function. Reactivating this enzyme allows cells to resume active ion exchange, gradually resolving poisoning symptoms.

The primary indication for this drug is specific antidote therapy for complications arising from cardiac glycoside treatment (digitalis toxicity).

Role in Complex Therapy

To successfully manage cardiac glycoside poisoning, Dimercaprol is used as part of combination therapy. It interacts with other treatments as follows:

Electrolyte replenishment ($K^+$ and $Mg^{2+}$). Once Dimercaprol frees $Na^+,K^+$-ATPase, the enzyme requires activators, specifically magnesium ions. Therefore, potassium chloride or combination products (e.g., Panangin, Asparkam) are co-administered. Magnesium initiates ATPase activity, which is necessary for the active transport of potassium ions into cardiomyocytes.
Combating calcium overload. To bind (chelate) $Ca^{2+}$ ions in the systemic circulation, edetate disodium (Trilon B) is administered intravenously.
Correction of conduction disturbances. If atrioventricular (AV) block develops, Atropine is the drug of choice. It blocks cardiac $M_2$ muscarinic receptors, eliminating the vagal inhibitory effect (n. vagus) on the AV node to improve conduction.

Formulations and Dosing Guidelines

The drug is available in two forms:

Powder (substance).
5% solution in 5 mL ampoules.

Routes of administration: subcutaneous (SC), intramuscular (IM), and intravenous (IV). Dosage is calculated strictly based on the patient's body weight. Standard regimen: 1 mL of 5% solution per 10 kg of body weight.

Prescription Examples

Example prescription for a 5% solution ampoule for a 50 kg patient (requires 5 mL, i.e., 1 ampoule per dose):

Rp.: Sol. Unithioli 5% - 5 ml D.t.d. N. 10 in ampull. S. Administer intramuscularly, 5 mL (based on 1 mL per 10 kg of body weight).

Example prescription for powder:

Rp.: Unithioli 1,0 D.t.d. N. 10 S. Follow protocol for solution preparation.

Mnemonic

Unithiol — Unloads Toxins, Donating Thiols (-SH groups) to save ATPase.

Frequently asked questions

How does Dimercaprol restore enzyme function?: The drug acts as a sulfhydryl (-SH) group donor. It binds the cardiac glycoside molecule via disulfide bridges, liberating the intrinsic thiol groups of $Na^+,K^+$-ATPase.
How do you calculate the dose of 5% Unithiol solution?: Dosage is calculated strictly by body weight: 1 mL of the 5% solution is required for every 10 kg of weight. It can be administered subcutaneously, intramuscularly, or intravenously.
Why is magnesium important alongside Unithiol when treating glycoside toxicity?: $Mg^{2+}$ ions are required activators of $Na^+,K^+$-ATPase. After Dimercaprol frees the enzyme from the glycoside, magnesium ensures active transport of potassium ions into the cardiomyocyte.
Can Dimercaprol be used to treat AV block caused by glycoside poisoning?: While the drug addresses the root cause by binding the glycoside, Atropine—which blocks $M_2$ receptors—is the drug of choice for the emergency correction of conduction disorders like AV block.

Go deeper

Structure and function of cardiomyocyte $Na^+,K^+$-ATPase.
Mechanism of cardiac glycoside toxicity.
Role of magnesium and potassium ions in maintaining resting membrane potential.
Pharmacodynamics of Atropine in bradyarrhythmias and AV blocks.
Mechanism of action of chelating agents using edetate disodium as an example.