DIMERCAPROL, BAL

Chemistry - A dithiol chelating agent, dimercaprol occurs as a colorless or nearly colorless, viscous liquid that is soluble in alcohol, vegetable oils, and water, but is unstable in aqueous solutions.
It has a very disagreeable mercaptan-like odor. The commercially available injection is a peanut oiland benzyl benzoate solution. Although the solution may be turbid or contain small amounts offlocculent material or sediment, this does not mean the solution is deteriorating.
Dimercaprol may also be known as BAL, British Anti-Lewisite, dimercaptopropanol, ordithioglycerol.

Storage, Stability, Compatibility

Dimercaprol injection should be stored below 40°C; preferably at room temperature (15-30°C).

Pharmacology - DIMERCAPROL, BAL

The sulfhydryl groups found on dimercaprol form heterocyclic ring complexeswith heavy metals, principally arsenic, lead, mercury and gold. This binding helps prevent or reduceheavy metal binding to sulfhydryl-dependent enzymes. Different metals have differing affinities forboth dimercaprol and sulfhydryl-dependent enzymes and the drug is relatively ineffective inchelating some metals (e.g., selenium). Chelation to dimercaprol is not irreversible and metals candissociate from the complex as dimercaprol concentrations decrease, in an acidic environment, or ifoxidized. The dimercaprol-metal complex is excreted via renal and fecal routes.

Uses, Indications

The principal use of dimercaprol in veterinary medicine is in treating intoxications caused by arsenical compounds. It is occasionally used for lead, mercury and gold intoxication.

Pharmacokinetics - DIMERCAPROL, BAL

After IM injection, peak blood levels occur in 30-60 minutes. The drug isslowly absorbed through the skin after topical administration.
Dimercaprol is distributed throughout the body, including the brain. Highest tissue levels arefound in the liver and kidneys.
Non-metal bound drug is rapidly metabolized to inactive compounds and excreted in the urine, bileand feces. In humans, the duration of action is thought to be about 4 hours, with the drugcompletely eliminated within 6-24 hours.

Contraindications, Precautions, Reproductive Safety

Dimercaprol is contraindicated in patients with impaired hepatic function, unless secondary to acute arsenic toxicity. The drug is alsocontraindicated in iron, cadmium, and selenium poisoning as the chelated complex can be moretoxic than the metal alone.
Because dimercaprol is potentially nephrotoxic, it should be used cautiously in patients withimpaired renal function. In order to protect the kidneys, the urine should be alkalinized to preventthe chelated drug from dissociating in the urine. Animals with diminished renal function or whodevelop renal dysfunction while on therapy should either have the dosage adjusted or discontinuetherapy dependent on the clinical situation.

Adverse Effects, Warnings

IM injections are necessary with this compound but can be verypainful, particularly if the drug is not administered deeply. Vomiting and seizures can occur withhigher dosages. Transient increases in blood pressure with concomitant tachycardia has been reported. Most adverse effects are transient in nature as the drug is eliminated rapidly.
Dimercaprol is potentially nephrotoxic.

Overdosage, Acute Toxicity

Symptoms of dimercaprol overdosage in animals include vomiting, seizures, tremors, coma and death. No specific doses were located to correspond with thesesymptoms, however.

Drug Interactions

Because dimercaprol can form a toxic complex with certain metals (cadmium, selenium, uranium and iron). Do not administer with iron or selenium salts. At least 24 hoursshould pass after the last dimercaprol dose, before iron or selenium therapy is begun.Drug/Laboratory Interactions - Iodine I131 thyroidal uptake values may be decreasedduring or immediately following dimercaprol therapy as it interferes with normal iodineaccumulation by the thyroid.