Chelation therapy
If acute arsenic poisoning is suspected, consult a clinical toxicologist early for advice on the use of chelation therapy. Chelation is the mainstay of treatment in acute arsenic poisoning and may be required for months. Oral chelation therapy is preferred and most Australian toxicology units stock succimer (dimercaptosuccinic acid [DMSA]). Parenteral chelation therapy can be used initially if oral chelation therapy with succimer is not immediately available or if the patient has severe gastrointestinal adverse effects to succimer.
None of the chelating agents discussed below are registered for use in Australia and all have limited availability through the Special access scheme. Treatment may be determined by which agent can be obtained in a timely fashion.
Oral chelation therapy
For oral chelation therapy, in adults and children, use:
succimer 10 mg/kg orally, 8-hourly for 5 days, followed by 10 mg/kg 12-hourly for at least a further 14 days and until urinary arsenic concentration is less than 50 micrograms/L in a 24-hour urine collection1. arsenic poisoning
Adverse effects of succimer include abdominal pain, transient rash, raised liver aminotransferase enzymes and neutropenia.
Parenteral chelation therapy can be used if oral chelation therapy with succimer is not immediately available or if the patient has severe gastrointestinal adverse effects to succimer.
Parenteral chelation therapy
Parenteral chelation therapy can be used if oral chelation therapy with succimer is not immediately available or if the patient has severe gastrointestinal adverse effects to succimer. Appropriate regimens for adults and children are:
1 dimercaptopropane-1-sulfonate (DMPS) 5 mg/kg intravenously, every 6 hours for 5 days2 arsenic poisoning
OR as combination therapy
2 dimercaprol 3 mg/kg intramuscularly, every 4 hours for 2 days, then reduce to 3 mg/kg every 12 hours for a further 5 to 7 days3 arsenic poisoning
PLUS
sodium calcium edetate (calcium EDTA) 50 to 75 mg/kg in crystalloid solution 500 mL4 intravenously over 24 hours, daily for up to 5 days5. arsenic poisoning
Sodium calcium edetate can be used as a single agent if the other parenteral agents are not available. It can cause kidney injury and prolonged treatment can lead to significant micronutrient deficiencies.
Treatment should be switched to succimer as soon as it becomes available (see Oral chelation therapy).
Monitoring and follow up after chelation therapy
Monitor blood arsenic concentrations weekly during chelation therapy. Serial concentrations can help to confirm effective treatment.
All chelation therapies carry the risk of micronutrient deficiency, including iron, zinc and copper. Blood concentrations of these elements should be checked before and during chelation therapy, and any deficiencies corrected.
Repeat full blood examination (looking for neutropenia) and liver biochemistry (looking for indicators of liver injury) after 5 days of chelation therapy.