About This Calculator

The Dimercaprol (BAL) dose calculator is designed to assist healthcare professionals in determining the appropriate dosing regimen for this chelating agent in cases of heavy metal poisoning. Dimercaprol, also known as British Anti-Lewisite (BAL), is administered via deep intramuscular injection and is used to treat poisoning by arsenic, gold, mercury, and as an adjunct in severe lead poisoning.

Outputs Explained

After entering the required patient data, the calculator provides the following key outputs for clinical use:

• Single Dose (mg): The calculated amount of dimercaprol in milligrams for a single administration based on patient weight and indication. For mercury poisoning, both initial and maintenance doses are shown.
• Volume to Inject (mL): The corresponding volume of medication to be drawn up for injection, based on the standard concentration of 100 mg/mL.
• Dosing Regimen Table: A detailed, day-by-day schedule outlining the dose per kilogram, administration frequency, number of doses per day, and total daily dose in milligrams.

How to Use the Tool

To ensure accurate calculations, please follow these steps:

1. Enter Patient Weight: Input the patient’s body weight. You can toggle between kilograms (kg) and pounds (lbs); the tool will automatically handle the conversion.
2. Select Indication: Choose the specific type of heavy metal poisoning from the dropdown menu. Options include severe or mild arsenic/gold poisoning, mercury poisoning, or lead poisoning.
3. Calculate and Review: Click the “Calculate Dose” button to generate the dosing plan. Carefully review all outputs and cross-verify them with clinical guidelines and institutional protocols before administration.

Dosing Overview

Dimercaprol dosing is weight-based and varies significantly by the type and severity of poisoning. It is supplied in a peanut oil base for deep IM injection only.

• Arsenic or Gold Poisoning: Mild cases are typically dosed at 2.5 mg/kg, while severe cases require 3 mg/kg. The regimen involves a tapering frequency, starting with doses every 4 hours and gradually decreasing to every 12 hours over approximately two weeks.
• Mercury Poisoning: Treatment begins with a higher initial dose of 5 mg/kg, followed by a maintenance dose of 2.5 mg/kg. The frequency is typically every 12 to 24 hours for up to 10 days.
• Lead Poisoning (Adjunct Therapy): For severe lead encephalopathy, dimercaprol is given at 4 mg/kg every 4 hours, usually in conjunction with edetate calcium disodium (CaNa2EDTA). The course typically lasts 5 to 7 days.

Switching Therapy

Dimercaprol is a parenteral agent used for the initial, critical phase of chelation. After a course of dimercaprol, a healthcare provider may decide to switch to an oral chelating agent, such as succimer (DMSA), for continued treatment, especially in cases of lead or mercury poisoning. This transition should only be made under the guidance of a toxicologist or physician experienced in chelation therapy, based on the patient’s clinical status and metal body burden.

Missed Dose Protocol

Maintaining a consistent dosing schedule is crucial for effective chelation and to prevent redistribution of heavy metals. If a dose is missed, contact the prescribing physician or a clinical toxicologist immediately for guidance. Do not double the next dose to make up for a missed one. The appropriate action will depend on the patient’s condition and the time elapsed since the dose was missed.

Safety Alerts

Dimercaprol use requires careful monitoring and adherence to safety protocols.

• Administration: For deep Intramuscular (IM) injection ONLY. Rotate injection sites to minimize local pain, irritation, and the risk of sterile abscesses.
• Adverse Effects: Hypertension and tachycardia are common. Monitor blood pressure and heart rate closely after administration. Other potential side effects include nausea, vomiting, headache, and a burning sensation in the mouth and throat.
• Contraindications: Do not use for poisoning by iron, cadmium, or selenium, as it forms toxic complexes with these metals.
• Cautions: Use with extreme caution in patients with G6PD deficiency due to the risk of hemolysis. Use cautiously in patients with hepatic impairment. Discontinue therapy if acute renal insufficiency develops.

Frequently Asked Questions (FAQ)

1. What does “BAL” stand for?

BAL stands for “British Anti-Lewisite,” which was its original name when developed as an antidote to the arsenic-based chemical warfare agent Lewisite during World War II.

2. Why is the injection volume calculated?

The calculator provides the volume in milliliters (mL) to help ensure accurate measurement and administration, as the drug is supplied at a concentration of 100 mg/mL.

3. Why is dimercaprol contraindicated in iron poisoning?

Dimercaprol forms a toxic complex with iron, which can increase, rather than decrease, systemic toxicity. Deferoxamine is the appropriate chelator for iron poisoning.

4. Can this calculator be used for pediatric patients?

The dosing principles are weight-based and apply to children, but pediatric use requires extreme caution and should be managed by a specialist. Always verify dosing with pediatric-specific resources.

5. How is a patient’s weight in pounds (lbs) converted?

The tool uses the standard conversion factor of 1 kilogram = 2.20462 pounds.

6. Why must urine be kept alkaline during therapy?

Maintaining an alkaline urine helps protect the kidneys by preventing the dissociation of the dimercaprol-metal complex, which can be nephrotoxic, especially at an acidic pH.

7. What is the significance of the peanut oil base?

Dimercaprol is formulated in peanut oil for IM administration. It is essential to screen patients for peanut allergies before use.

8. Why is the dosing frequency tapered for arsenic poisoning?

The frequency is tapered down as the patient’s acute toxic symptoms resolve and the body burden of the metal decreases. This schedule is designed to balance efficacy with the risk of adverse effects from the chelator itself.

References

• Dimercaprol Injection, USP – FDA Prescribing Information
• WHO Model Formulary: Dimercaprol
• Nelson, L. S., Howland, M. A., Lewin, N. A., Smith, S. W., Goldfrank, L. R., & Hoffman, R. S. (2019). Goldfrank’s toxicologic emergencies (11th ed.). McGraw-Hill Education.
• DailyMed – Dimercaprol Injection