What are the recommended dosing regimens of dimercaptosuccinic acid (DMSA) for children and adults with lead poisoning, and for acute mercury or arsenic poisoning?

DMSA Dosing for Heavy Metal Poisoning

For lead poisoning in children, administer DMSA 1050 mg/m²/day (approximately 30 mg/kg/day) divided into three doses for 5 days, followed by 700 mg/m²/day for 14 days to prevent rebound; for adults with lead poisoning, use 30 mg/kg/day for 5 days with repeated courses as needed after 1-week treatment-free intervals.

Lead Poisoning Dosing

Children

• Initial course: 1050 mg/m²/day (approximately 30 mg/kg/day) orally for 5 days 1
• Outpatient continuation: 700 mg/m²/day for 14 days following the initial course to delay blood lead rebound and reduce need for repeated hospitalizations 1
• This regimen decreased blood lead by 61% during the initial 5-day course and maintained blood lead at 50% of pretreatment values after the 14-day continuation 1

Adults

• Standard dose: 30 mg/kg/day orally for 5 days 2, 3
• Repeated courses: After at least 1 week treatment-free interval to allow lead redistribution from bone 3
• Severe poisoning: May extend beyond 5 days with benefit in heavily poisoned patients 3
• This dose increases urinary lead excretion 12-fold (median) and reduces blood lead concentrations by 50% or more 2

Important dosing principle: 30 mg/kg/day is significantly more effective than 10 or 20 mg/kg/day for enhancing urinary lead excretion 3. Lower doses should not be used.

Mercury and Arsenic Poisoning

Acute Mercury Poisoning

• Dose: 30 mg/kg/day for 5 days 4
• DMSA increased daily mercury urinary excretion 1.5- to 8.4-fold in case reports 4
• Note: DMPS (dimercaptopropane sulfonate) is the recommended first-line agent for acute inorganic mercury poisoning, though DMSA has shown efficacy 5

Arsenic Poisoning

• Acute poisoning: Four 5-day courses of 30 mg/kg/day successfully reduced serum arsenic from 2,871 µg/L to 6 µg/L over 30 days 6
• DMSA decreased plasma arsenic concentration by 50% within 7 days in acute poisoning 4

Practical Administration Details

Dosing Schedule

• Divide the total daily dose into three doses throughout the day
• Administer orally with or without food
• Maximum enhancement of urinary lead elimination typically occurs with the first dose 3

Treatment Course Structure

The evidence supports two approaches:

1. Multiple short courses: 5-day courses separated by at least 1-week treatment-free intervals 3
2. Extended initial course: 5 days at full dose followed by 14 days at reduced dose (700 mg/m²/day for children) 1

Both approaches are effective; the choice depends on severity and blood lead rebound patterns.

Clinical Response Monitoring

• Symptomatic improvement: Most patients report improvement within 2 days of treatment 2, 3
• Urinary lead excretion: Expect 5- to 20-fold increase over baseline during treatment 3
• Blood lead reduction: Typically falls to 50% or less of pretreatment concentration after 5 days 3
• Individual variation: Response varies substantially between patients 2, 3

Safety Considerations

Common Adverse Effects

• Transaminase elevation: Transient modest rise in 14-60% of patients, typically not clinically significant 2, 3
• Skin reactions: Occur in approximately 6% of patients, occasionally severe 3
• Essential metal depletion: Increases urinary copper and zinc excretion but not to clinically important extent 3

Special Populations

• Pregnancy: DMSA is not teratogenic but caused maternal and fetal toxicity at high doses (100-1000 mg/kg/day) in animal studies; sodium calcium edetate is generally preferred 3
• G6PD deficiency: DMSA was well tolerated in two patients with homozygous G6PD deficiency 1
• Concurrent iron supplementation: Safe to administer together 1

Contraindications and Precautions

• Monitor liver function during treatment due to transaminase elevation risk
• Watch for skin reactions, particularly in first course
• Do not use if patient has history of severe mucocutaneous reactions to DMSA 2

Key Clinical Pitfalls

Do not use lower doses: 30 mg/kg/day is the established effective dose; 10 or 20 mg/kg/day are inadequate 3.

Do not skip the treatment-free interval: When giving repeated courses, allow at least 1 week between courses to permit lead redistribution from bone to blood where it can be chelated 3.

Do not expect cognitive improvement in chronic childhood lead exposure: While DMSA effectively reduces blood lead, it did not improve cognition in children under 3 years with mild lead poisoning, as neurological damage likely occurred during critical developmental periods 3.

Do not use DMSA alone for lead encephalopathy: Adults with blood lead ≥100 µg/dL almost always warrant chelation, but severe cases may require more aggressive therapy 7.