Usage
- Dimercaprol is prescribed for the treatment of acute poisoning by heavy metals like arsenic, mercury, gold, and lead. It is also used for poisoning by antimony, bismuth, and possibly thallium. In lead poisoning, it is used in conjunction with calcium disodium edetate (EDTA), especially in children.
- Pharmacological classification: Chelating agent.
- Mechanism of action: Dimercaprol’s sulfhydryl groups bind to heavy metals, forming stable, non-toxic complexes that can be excreted in bile and urine. This prevents or reverses the binding of these metals to sulfhydryl-containing enzymes, thus reducing their toxic effects.
Alternate Names
- BAL (British Anti-Lewisite)
- Brand names: BAL in Oil
How It Works
- Pharmacodynamics: Dimercaprol increases the excretion of heavy metals, reducing their toxicity. It competes with endogenous sulfhydryl groups on enzymes for binding with heavy metals, thus preventing or reversing the inhibition of these enzymes. It also promotes the mobilization of metals from tissues. The effectiveness varies depending on the specific metal, route of exposure, and time elapsed since exposure.
- Pharmacokinetics: Administered intramuscularly (IM), dimercaprol is rapidly absorbed and distributed throughout the body. Peak plasma levels reached within 30–60 minutes. It is metabolized in the liver and excreted primarily by the kidneys as metal complexes and inactive metabolites. Elimination half-life is relatively short (around 4 hours).
- Mode of Action: Dimercaprol’s sulfhydryl (-SH) groups have a high affinity for heavy metals, particularly arsenic, mercury, gold, and lead. It forms stable chelates with these metals by displacing them from their binding sites in tissues and enzymes. The resulting dimercaprol-metal complexes are water-soluble and can be readily excreted, preventing further tissue damage.
- Elimination pathways: Primarily renal excretion. Biliary excretion also occurs. Metabolism in the liver to inactive forms, although it is unknown if specific CYP enzymes are involved.
Dosage
Standard Dosage
Adults:
- Arsenic/Gold poisoning (mild to moderate): 2.5 mg/kg IM every 4 hours for 2 days, then every 6 hours on day 3, then twice daily for 10 days or until recovery.
- Arsenic/Gold poisoning (severe): 3 mg/kg IM every 4 hours for 2 days, then every 6 hours on day 3, then twice daily for 10 days or until recovery.
- Mercury poisoning: 5 mg/kg IM initially, then 2.5 mg/kg IM every 12-24 hours for 10 days.
- Lead poisoning (with CaNa2 EDTA): Initially, 4 mg/kg IM, followed by 3-4 mg/kg every 4 hours, alongside EDTA, for 3-5 days. The course may be repeated if necessary based on blood lead levels.
Children:
- Dosage calculated based on body weight, using the same unit dose per kg as for adults in similar clinical situations.
- Pediatric safety: Fever is a common side effect, especially after the second or third dose. Monitor for any adverse reactions.
Special Cases:
- Elderly Patients: Use with caution due to potential renal impairment. Monitor renal function.
- Patients with Renal Impairment: Discontinue or use with extreme caution if renal insufficiency develops during treatment. Monitor urine pH and renal function closely. Dosage reduction may be necessary.
- Patients with Hepatic Dysfunction: Contraindicated, except in cases of arsenic-induced jaundice.
- Patients with Comorbid Conditions: Use with caution in patients with hypertension, G6PD deficiency, peanut allergy.
Clinical Use Cases
Dimercaprol is generally not indicated for use in clinical situations like intubation, surgical procedures, mechanical ventilation, or intensive care settings, except in cases of heavy metal poisoning occurring in these contexts. Dosage in such instances would follow the standard guidelines, adjusted according to the specific metal and the patient’s condition. In emergency situations involving heavy metal poisoning, immediate administration of dimercaprol as per standard protocols is crucial.
Dosage Adjustments
Dosage adjustments may be required based on the specific metal involved, severity of poisoning, patient’s clinical response, and renal function. Close monitoring of the patient’s condition and laboratory parameters is essential for optimizing treatment.
Side Effects
Common Side Effects
- Hypertension
- Tachycardia
- Nausea, vomiting
- Headache
- Burning sensation in the mouth, throat, eyes
- Conjunctivitis, lacrimation, rhinorrhea
- Pain and sterile abscess at injection site
- Fever (in children)
- Tightness in chest, limbs, or abdomen
Rare but Serious Side Effects
- Seizures
- Coma
- Kidney damage
- Hemolytic anemia (especially in G6PD deficiency)
Long-Term Effects
Chronic complications from prolonged use are rare, as treatment is usually short-term. However, kidney damage can be a long-term consequence of severe poisoning or improper dosing.
Adverse Drug Reactions (ADR)
Severe hypertension, seizures, coma, renal failure, and hemolytic anemia require immediate medical attention.
Contraindications
- Hypersensitivity to dimercaprol or peanut oil (the vehicle for injection)
- Hepatic insufficiency (except in arsenic-induced jaundice)
- Iron, cadmium, or selenium poisoning (dimercaprol can form toxic complexes with these metals)
- Not for intravenous administration
Drug Interactions
- Iron supplements and preparations: Increased risk of nephrotoxicity. Avoid concomitant use.
- Other chelating agents (e.g., EDTA): Used in combination for lead poisoning, but administer at separate injection sites.
- Drugs metabolized by the liver: Dimercaprol might affect their metabolism due to its own hepatic metabolism. Monitor carefully.
Pregnancy and Breastfeeding
- Pregnancy Safety Category: C (Animal studies show risk, but no adequate human studies.)
- Fetal risks: Potential for embryotoxic and teratogenic effects. Use only if clearly needed and if potential benefits outweigh risks.
- Breastfeeding: Excretion in breast milk is unknown. Avoid use during breastfeeding or discontinue breastfeeding while using dimercaprol.
Drug Profile Summary
- Mechanism of Action: Chelates heavy metals, enhancing excretion and reducing toxicity.
- Side Effects: Hypertension, tachycardia, nausea, vomiting, headache, injection site pain, fever (in children), burning sensation in the mouth, throat, and eyes. Rarely: seizures, coma, renal failure.
- Contraindications: Hypersensitivity, hepatic insufficiency (except arsenic-induced jaundice), iron/cadmium/selenium poisoning, not for IV use.
- Drug Interactions: Iron salts (increased nephrotoxicity), EDTA (co-administration at separate injection sites).
- Pregnancy & Breastfeeding: Category C; use with caution if benefits outweigh risks. Excretion in breast milk is unknown. Avoid during breastfeeding.
- Dosage: Varies depending on the metal and severity of poisoning (2.5-5 mg/kg IM). See detailed dosage guidelines above.
- Monitoring Parameters: Blood pressure, heart rate, renal function, urine pH, blood metal levels, liver function tests (if necessary).
Popular Combinations
- Calcium disodium edetate (CaNa2 EDTA): Used concurrently with dimercaprol for lead poisoning, especially in cases with encephalopathy.
Precautions
- General Precautions: Pre-screening for allergies to dimercaprol or peanuts, hepatic and renal function assessment. Monitor vital signs, urine output, and fluid balance.
- Specific Populations: See “Special Cases” under “Dosage.”
- Lifestyle Considerations: Maintain adequate hydration.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Dimercaprol?
A: The dosage varies depending on the type and severity of heavy metal poisoning. Refer to the detailed dosage guidelines provided above.
A: Dimercaprol is primarily used for acute poisoning. For chronic exposure, other chelating agents with better safety profiles for long-term use might be preferred.
Q3: What are the most serious side effects of dimercaprol?
A: Seizures, coma, renal failure, and hemolytic anemia are the most serious potential side effects.
Q4: Is dimercaprol safe to use in patients with peanut allergies?
A: No, dimercaprol is contraindicated in patients with peanut allergies because the injection is formulated in peanut oil.
Q5: How is dimercaprol administered?
A: Dimercaprol is administered via deep intramuscular injection (IM).
Q6: What should be monitored during dimercaprol treatment?
A: Blood pressure, heart rate, renal function, urine pH, and blood metal levels should be closely monitored.
Q7: Can dimercaprol be given intravenously?
A: No, dimercaprol should not be administered intravenously.
Q8: What is the role of dimercaprol in lead poisoning?
A: Dimercaprol is used as an adjunct therapy with calcium disodium edetate in lead poisoning, especially in children and cases with encephalopathy.
Q9: Can dimercaprol be used in patients with liver disease?
A: Dimercaprol is contraindicated in patients with hepatic insufficiency, except for arsenic-induced jaundice.
