Poisons, poisoning and antidotes- how are they linked?
Poisons are substances that cause damage or death of living tissues when swallowed, injected or inhaled. An antidote is a drug, chelating substance, or a chemical which counteracts or neutralizes the effects of another drug or a poison. This article focuses primarily on the types of poisons, poisoning signs & symptoms, management of poisoning with antidotes and other measures.
Poisoning can be classified as
- Accidental poisoning
- Deliberate self-poisoning
- Non-accidental poisoning
- Homicidal poisoning
- Occupational poisoning
- Environmental poisoning
Causes of poisoning
Poisoning can occur due to chemicals from various sources. They can be in solid, liquid (volatile or non-volatile) or gaseous forms. Even though poisons can be of various origins, they are majorly classified into the following
- Agricultural, industrial and household chemicals.
- Heavy metals
- Pharmacological drugs (usually overdose or interaction)
- Illegal drugs
- Biological poisons (spoiled food, plant and animal sources)
Signs and symptoms of poisoning
The signs and symptoms of poisoning vary depending on the nature of the poison/toxin and the route of administration. However, there are some generalized symptoms of poisoning such as
- Weakness
- Dilated or constricted pupils
- Difficulty in breathing
- Vomiting or nausea
- Dizziness
- Disorientation
- Stomach pain
- Chills
- Headache
- Loss of consciousness or coma (severe cases)
- Double vision
- Cyanosis
- Increased salivation or foaming around mouth
- Sores or redness around mouth
- Skin rash
- Seizures
Principles of management of poisoning
Management of poisoning requires a sound knowledge about poisoning and swiftness in management.
- Initial assessment of poisoning
- Resuscitation
- Supportive management
- Measures to prevent further drug absorption
- Enhancement of elimination of the poison
- Administering specific antidotes
- Psychiatric and social assessment
1. Initial assessment of poisoning
Finding the cause for poisoning is crucial in managing it.
- A thorough history from the patient or the bystander (the identity of the substance, the dose, the time elapsed after ingestion, did the patient vomit or not, did the patient consume alcohol along with the poison).
- Clinical examination -(head to toe scheme/method) along with
- Necessary laboratory investigations are necessary in order to identify the poison and treat appropriately (urine analysis, blood analysis and other specific tests).
A response to a particular antidote may also help in finding the of poison, eg. dilation of constricted pupils and increased respiratory rate after administering naloxone may be a case of opioid poisoning. A physician could also get help from a poison information center.
2. Resuscitation
Standard resuscitation procedures must be carried out in order to stabilize the patient and prevent further complications. Maintaining ABC (airway, breathing and circulation) is the initial and crucial step in management of poisoning.
3. Supportive management
The majority of patients admitted to hospital will require only observation along with medical and nursing supportive measures while they metabolize and eliminate the poison. Some will require specific measures (reduce absorption or increase elimination). Few of them will require administration of a specific antidote and very few will need intensive care facilities. In case of a serious overdose, always obtain the latest advice on management.
Along with maintaining airway and ventilation and treating hypotension, the following conditions should be managed as well
- Convulsions
- Cardiac arrhythmias
- Acidosis
- Hypoxia
- Electrolyte imbalance
- Hypothermia
- Immobility
- Rhabdomyolysis
4. Measures to prevent further drug absorption
Gut decontamination could be done in some cases by
- Emesis
- Gastric lavage
- Whole-bowel irrigation
Oral absorbents like activated charcoal can be used in specific cases.
5. Enhancement of elimination of poison
This can be done by
- Altering urine pH and Forced diuresis
- Dialysis
- Hemoperfusion
- Intestinal dialysis or enteral removal
6. Administering specific antidotes
Antidotes are used in management of specific poisoning cases against certain poisons or toxins. In general they are used in the early stages of poisoning and are used after weighing their risks and benefits. Antidotes are classified based on their mechanisms, efficacy, class of poisons they are used against and based on urgency of clinical use. They are classified into the following main categories based on their mechanism
General / universal antidotes
Adsorbs the toxin and prevents its systemic absorption. Eg. activated charcoal
Chelating agents
The sulfhydryl groups of dimercaprol react with certain heavy metals to form a complex thereby preventing or reversing the metallic binding of enzymes containing sulfhydryl groups. This sulfhydryl-heavy metal complex is then excreted in the urine.
Detoxification accelerators
They help to speed up the process of conversion of the poison to a non-toxic substance. Eg. acetylcysteine in paracetamol poisoning
Toxicity reducers
These antidotes reduce the toxicity of poisons by either by converting the poison to a less toxic substance or by inhibiting the conversion to a potentially toxic substance.
Eg. Ethanol inhibits the conversion of methanol to toxic metabolites by competing with methanol for the enzyme alcohol hydrogenase that is required for the process
Receptor site blockers or inhibitors
Some antidotes bind to the receptor site of the toxin and prevent the toxin from exerting its effect. Eg. Atropine blocks the muscarinic receptor site in case of organophosphate poisoning.
Toxic effect bypass
Eg. Oxygen in cyanide poisoning.
Poisons and antidote chart for poisoning management
Some antidotes act against specific poisons. On the other hand, some (activated charcoal) are used in the management of poisoning of many poisons. Based on the recommendations, their stocking value changes (especially in the emergency department). Management of poisoning with antidotes depends on the type of poison and other factors.
7. Psychiatric and social assessment
Perform psychiatry and social assessment regardless of the type of poisoning to recover from the trauma (especially in deliberate poisoning).
Written by Auxi Arobana. R