Arsenic

Overview

  1. Uncommon but potentially fatal. Often chronic. Inorganic toxicity more common. Greater with tri- rather than penta-valent arsenic. Therapeutic use in acute promyelocytic leukaemia.

Toxic mechanism

  1. As3 :
    1. Binds to many cell enzymes, inhibits cellular respiration & DNA replication/repair. Reactive O2 intermediates.

Toxicokinetics

  1. Abs by GIT, skin & lungs. Distributes to kidney, liver then lungs, CNS/PNS and nails. Liver met. T½5d

Clinical features

  1. Acute:
    1. Rapid dev of metallic taste, hypersalivation & slight garlic odour, severe N&V & rice water diarrhoea±blood, abdo pain. Followed by encephalopathy, seizures, dysrhythmias, ARDS, RF, liver injury. Later marrow depression, alopecia & neuropathy.
  2. Chronic:
    1. Insidious onset over years of constitutional symptoms, cutaneous lesions, nail changes, painful peripheral neuropathy and skin/bladder Ca.

Investigations

  1. Screening: ECG, paracetamol, BSL
  2. Specific bloods:
  3. Spot (Norm<30µg/L or 4.0µmol/L) & 24hr (Norm<50µg/L or 6.65µmol/L) urinary arsenic, blood level if anuric, FBC, UEC, LFT, ABG, CXR/AXR

Risk assessment

  1. Chronic intoxication can follow long-term drinking of artesian well water. Acutely <5mg → mild GIT symptoms, but >100–300mg (child <1mg/kg) potentially lethal.

Management

Resus & Supportive Care

  1. Rarely req. Mannitol & dexamethasone if cerebral oedema.
  2. Fluid status.

Decontamination

  1. Remove source. Remove clothes & wash skin if dermal exposure.
  2. WBI if co-operative & ingested inorganic As trioxide (shown on AXR).

Enhanced Elimination

  1. Polythiol resin may reduce organic Hg enterohepatic circulation.

Antidote

  1. Chelation therapy (see Antidotes)

Disposition

  1. Depends on severity.

Notes

  1. Sources:
    1. inorganic (ground water, soil, industrial, traditional remedies)
    2. organic (fish: but in non-toxic forms, more toxic is trypanosomiasis Rx melarsoprol).
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