Poisons and Poisoning

Introduction

Poisons are chemical or physical agents that produce adverse responses in biological systems.

Paracelsus famously said that” All things are poison and nothing without poison. Solely, the dose determines that a thing is not a poison”

Poisoning on the other hand is the ingestion by, or exposure of a patient to excessive doses of a medicine or other substances that may cause harm.

The pattern of poisoning may be influenced by age and gender.

Poison may occur in the following ways:

• Self poisoning (may be suicidal or
  parasuicide)
• Accidental
• Homicidal
• Occupational
• Environmental

Common substances causing poisoning include (but are not limited to):

• Pharmaceuticals
  • Analgesics, hypnosedatives, antidepressants, alcohol
• Petroleum distillates
• Industrial chemicals
• Agrochemicals
• Household products
• Natural toxins
• Toiletries

Duration of exposure:

Acute: if exposure occurs for less than 24
hours. To be described as acute toxicity,
the adverse effect must occur within 14 days of exposure.

Subacute: if exposure occurs for up to 1 month.

Subchronic: if exposure occur for between 1-3 months.

Chronic: if exposure occur for > 3 months.

Clinical presentation of poisoning

Determined (amongst others) by:

• Dose and duration following exposure
• Type of Agent
• Inherent toxicity
• Concurrent therapy
• Co-existing disease states etc

This guideline provides only a brief
overview.

NB: you can  seek advice from standard texts in medicine and toxicology, in the absence of a Poison Information
Centre

Principles of management of poisoning

Aims:

1. Stabilize the patient
2. Decrease the absorption of the substance
3. Increase elimination of the substance
4. Prevent and treat complications
5. Reduce the risk of future occurrence.

Management:

1. Emergency stabilization

• Remove the patient from the environment if there is immediate sign of danger (important in environmental poisoning).
• Provide fresh air and oxygen
  (respiratory decontamination)

Life-saving measures take priority
over all other decontamination.
techniques.

The following ABC approach is
recommended:

• A. Establish a clear Airway (patient may have to be intubated if they are
  unconscious; all patient should be
  placed in left lateral position to
  prevent aspiration of poison and gastric content)
• B. Ensure adequate Breathing and
  ventilation (Give high flow oxygen,
  except in paraquat Poisoning where
  this may worsen mild-moderate.
  hypoxia)
• C. Ensure adequate Circulation
• D. Address Drug-induced depression of the central nervous and respiratory systems.
• E. Correct any Electrolyte and
  metabolic abnormalities.
  (hypoglycemia and altered
  potassium handling are common in severe poisoning, cardiac monitoring for arrhythmias may be required especially in poisoning with TCA)

2. Clinical Evaluation

• Detailed history, physical examinations and appropriate
  investigations (Remember that
  absolutely diagnostic features are
  rare, however, some recognition of
  some toxidromes may give a clue e.g. pinpoint pupil in opioid poisoning).
• Information from relatives, friends,
  and emergency services personnel
  may be very useful.
• The patient may have no symptoms
  and signs when seen early in the course of the poisoning
• Amount, route and extent of exposure should be ascertained.
• Check for comorbidities
• Calm the patient down
• Appropriate laboratory investigations (blood screen, urine
  screen, blood biochemistry, liver.
  enzymes etc).
  • NB: Blood or other specimen assay may be very important to determine if the condition is actually a case of drug poisoning for legal purposes)
• Watch out for and control convulsions, hypothermia etc

3. Decrease the absorption of the substance.

Principle:

• It is based on the presumption that both the dose and duration of exposure are determinants of toxicity, and limiting continued exposure is beneficial.

Skin and mucuous areas:

• Flushing the areas (e.g. skin and eyes) with large volumes of water/normal saline to remove the toxic substance

Gut decontamination:

• Induced emesis: where there are no contraindications.
• Gastric lavage: Most effective when used within the 1″ hour of poisoning.
• Activated charcoal: Adsorb drugs
  and other substances in a non
  specific manner and reduce.
  absorption into the body. Repeated
  doses may be used in cases of poisons with drugs known to undergo entero-hepatic or entero-enteric recirculation (e.g. carbamazepine, cardiac glycoside, dapsone, phenobarbitone, quinine and theophylline).
  • NB: Activated charcoal is very
    unpalatable and conscious patients must be made to understand this. Substances like boric acid, cyanide, ethanol, ethylene glycol, iron, lithium, malathion, methanol, petroleum products and strong acids and alkalis are not adsorbed by activated charcoal.
• Gastric aspiration: should be
  considered in a patient that has
  ingested potentially life-threatening
  doses of drugs that are not adsorbed by oral activated charcoal (e.g. Lithium and Iron)
• Cathartics whole bowel irrigation: osmotic cathartics are no longer recommended because of the risk of electrolyte abnormality. Whole bowel irrigation may be performed to enhance rectal elimination of unabsorbed drugs.VA combination of the above methods may be used.

4. Increase elimination of poisons

Clearance of the toxic substances may be enhanced by:

• Manipulation of urine pH
• Haemodialysis/Haemoperfusion

5. Use specific Antidotes

An antidote is a drug that antagonizes the toxicity of another substance in a specific manner.

Examples of common antidotes are:

• Naloxone for opioids
• N-acetylcysteine for paracetamol
• Flumazenil for benzodiazepines
• Penicillamine for copper and lead
• Digoxin-specific antibody for
  digoxin
• 100% oxygen for carbon monoxide etc

6. Treat complications

• Treat dysrhythmia, hypoxia,
  hypotension, convulsions and
  hypothermia
• Reduce the risk of future occurrence
• This may involve counselling and psychiatrist support