Introduction to chemotherapy and toxicology



Toxicology

The traditional definition of toxicology is "the science of  poisons.“
 It is a combination of two Greek words  
Toxicon -Poison
Logos -study 
“All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy”
Paracelsus (Grand Father of Toxicology)
The  modern definition of toxicology is "the study of the  adverse effects of toxic agents on living organisms 
The adverse events of drugs, chemicals or any poison on the environment and living organisms including humans and animals with their detection, symptoms, pathogenesis, mechanism and treatment can be studied by a branch of science called toxicology.

Main focus
Toxicologists mainly focus to get following important information about poison:
  • Detection of poison
  • Occurrence of poison
  • Properties of poison
  • Effects of poison
  • Treatment of poison
  • Poison regulation. 
So toxicology studies involve
  • Toxicological studies involve
  • Identification of toxic agents
  • Route of exposure
  • Dose response relationship
  • Toxicokinetics
  • Toxicodynamics
  • Diagnosis and treatment
  • Risk assessment
  • Safety measures and awareness

Effects of toxicants


Irreversible Effects 
  • Carcinogen - causes cancer
  • Mutagen - causes chromosome damage
  • Reproductive hazard - damage to reproductive system
  • Teratogen - causes birth defects
May or may not be reversible 
  • Dermatotoxic – affects the skin
  • Hemotoxic – affects blood
  • Hepatotoxic – affects liver
  • Nephrotoxic – effects kidneys
  • Neurotoxic – affects nervous system
  • Pulmonotoxic – affects lungs

Branches of toxicology
There are various branches of toxicology as outlined below:
  1. Analytical toxicology
  2. Applied toxicology
  3. Clinical toxicology
  4. Veterinary toxicology
  5. Forensic toxicology
  6. Environment toxicology
  7. Industrial toxicology

1. Analytical toxicology

It is the branch of toxicology which deals with the study of detection and assay of poisonous chemicals including their metabolites that could affect the biological system. 

2. Applied toxicology

It is the application of new and modern methods or technologies for early detection of toxicants in the field setting or practice area. 

3. Clinical toxicology

It is mainly involved in the study of diagnosis and treatment of poisoning that can occur in humans.

4. Veterinary toxicology

Veterinary toxicology focus in the study of diagnosis and treatment of animal poisoning including the transmission of toxin from animals to humans via milk, meat, fish, foodstuff and etc. 

5. Forensic Toxicology

This is concerned with medico-legal aspects of the harmful effects of chemicals on humans and animals. 

6. Environmental toxicology

It is the branch of toxicology in which study of the presence of different toxicants including their metabolites and degradation products in the environment and their effects on humans and animals. 

7. Industrial toxicology

 It is the study of the selective and specific areas of environmental toxicology.

Important terminologies

Toxic agent

  • Anything that can produce an adverse biological effects.
  • It may be chemical, physical,  or biological in form.
  • For example, toxic agents maybe
  • Chemical (such as cyanide) 
  • Physical (such as  radiation) 
  • Biological (such as snake venom).

Poison

  • Poisons are substances that cause harm to organisms when sufficient quantities are absorbed, inhaled or ingested

Toxicants

  • Substances producing adverse biological effects of any kind.
  • May be chemical or physical in nature.
  • Effects may be acute or chronic.

Toxins

  •  Peptides or proteins produced by living organisms.
  • Venoms are toxins injected by a bite or sting.

Exposure

  • Contact with a chemical. The most common routes are inhalation, skin contact, and also by oral ingestion. 
Routes of exposure are
  • Inhalation (mouth or nose to lungs) then into the blood.
  • Ingestion (mouth to the stomach) then into the blood.
  • Injection (cuts, punctures in the skin) into the blood.
  • Dermal absorption (through the skin) into the blood.

Duration of exposure

  • Acute
  • Subacute
  • Sub Chronic 
  • Chronic

DOSE

The amount of chemical administered. It is a measure of exposure.

DOSE –RESPONSE

The relationship between the dose of a chemical and the degree/severity of the resulting effect.
There are two types of dose response relationship
  1. Graded type
  2. Quantal type

1. Graded dose-response


  • A quantitative response in which an increased dose of a drug produces varying changes in effect.
  • The dose which produces the first noticeable effect is called the threshold dose.
  • Further, an increase in dose results in a larger effect until the maximum effect is reached. This is called the ceiling effect. 
  • And further increase in dose doesn’t cause a further increase in the effect.

2. Quantal dose response

  • It is also known as all or none response of drug.
  • Either there will be a response or either there will be no response, Response will dead or alive, cured and not cured.
  • In this study, each animal is categorized as responding and non-responding according to the predetermined response.
  • The pre-determined response is death in toxicology.

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