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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