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 oil and benzyl benzoate solution. Although the solution may be turbid or contain small amounts of flocculent material or sediment, this does not mean the solution is deteriorating.
Dimercaprol may also be known as BAL , British Anti-Lewisite , dimercaptopropanol , or dithioglycerol .
Storage/Stability/Compatibility - Dimercaprol injection should be stored below 40°C; preferably at room temperature (15-30°C).
Pharmacology - The sulfhydryl groups found on dimercaprol form heterocyclic ring complexes with heavy metals, principally arsenic, lead, mercury and gold. This binding helps prevent or reduce heavy metal binding to sulfhydryl-dependent enzymes. Different metals have differing affinities for both dimercaprol and sulfhydryl-dependent enzymes and the drug is relatively ineffective in chelating some metals (e.g., selenium). Chelation to dimercaprol is not irreversible and metals can dissociate from the complex as dimercaprol concentrations decrease, in an acidic environment, or if oxidized. 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 - After IM injection, peak blood levels occur in 30-60 minutes. The drug is slowly absorbed through the skin after topical administration.
Dimercaprol is distributed throughout the body, including the brain. Highest tissue levels are found in the liver and kidneys.
Non-metal bound drug is rapidly metabolized to inactive compounds and excreted in the urine, bile and feces. In humans, the duration of action is thought to be about 4 hours, with the drug completely 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 also contraindicated in iron, cadmium, and selenium poisoning as the chelated complex can be more toxic than the metal alone.
Because dimercaprol is potentially nephrotoxic, it should be used cautiously in patients with impaired renal function. In order to protect the kidneys, the urine should be alkalinized to prevent the chelated drug from dissociating in the urine. Animals with diminished renal function or who develop renal dysfunction while on therapy should either have the dosage adjusted or discontinue therapy dependent on the clinical situation.
Adverse Effects/Warnings - IM injections are necessary with this compound but can be very painful, particularly if the drug is not administered deeply. Vomiting and seizures can occur with higher 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 these symptoms, 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 hours should pass after the last dimercaprol dose, before iron or selenium therapy is begun.
Drug/Laboratory Interactions - Iodine I131 thyroidal uptake values may be decreased during or immediately following dimercaprol therapy as it interferes with normal iodine accumulation by the thyroid.
For arsenic toxicity:
a) Dimercaprol therapy in horses is difficult because it must be used acutely and any substantial delays in treatment significantly decrease its effectiveness, as well as the amounts of dimercaprol that are required and the necessity to inject the drug IM. If available, the dose is: 5 mg/kg IM initially, followed by 3 mg/kg IM q6h for the remainder of the first day, then 1 mg/kg IM q6h for two or more additional days, as needed. (Oehme 1987a) (Note: Refer to this reference for additional information on the use of sodium thiosulfate and protective laxative therapy.)
Monitoring Parameters -
1) Liver function
2) Renal function
4) Hydration and perfusion status
5) Electrolytes and acid/base status
6) Urinary pH
Client Information - Because of the potential toxicity of this agent and the seriousness of most heavy metal intoxications, this drug should be used with close professional supervision only. Dimercaprol can impart a strong, unpleasant mercaptan-like odor to the animal’s breath.
Dosage Forms/Preparations/FDA Approval Status/Withholding Times -
Veterinary-Approved Products: None
Dimercaprol Injection 100 mg/ml (for IM use only) in 3 ml amps; BAL in Oil® (Becton Dickinson); (Rx)
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