Toxicology Introduction PDF

INTRODUCTION  Toxicology: toxico = poison Logy = science Is the study of the adverse effects of xenobiotics on living systems; or simply it can be defined as the science that deals with poisons.  The toxicologist is trained to examine the nature of these adverse effect...

INTRODUCTION  Toxicology: toxico = poison Logy = science Is the study of the adverse effects of xenobiotics on living systems; or simply it can be defined as the science that deals with poisons.  The toxicologist is trained to examine the nature of these adverse effect &the probability of their occurrence.  Poison: is any chemical substances or compounds that affect the living organisms &cause changes in the function, morphology &may cause death of the cells.  Toxin: is a poisonous substance that is a specific product of the metabolic activities of a living organism and is usually very unstable, notably toxic when introduced into the tissues, and typically capable of inducing antibody formation.  venoms are toxins which are injected by a bite or sting (this is exclusive to animals). Note that the differences between venom and other poisons is the method of delivery.  Side effects: are nontherapeutic reactions to a drug that are transient and may not require any nursing intervention  Classification of toxicology : The activities of toxicologist can be classified in to: 1. Descriptive toxicologist: concerned directly with toxicity testing. The appropriate toxicity test in experimental animals are designed to yield information that can be used to evaluate the risk posed to man &the environment by exposure to specific chemicals. 2. Mechanistic toxicologist: concerned with elucidating the mechanism by which chemicals exert their toxic effect on living organisms. 3. Regulatory toxicology: has responsibility of deciding (on the basis of data provided by the descriptive toxicologist) whether or not a drug or chemical has a low enough risk to be marketed for described 4. Forensic toxicology: it aids in establishing the cause of death &elucidating its circumstances in a postmortem investigation. 5. Clinical toxicology: concerned with diseases caused by or associated with toxic substances. 6. Environmental toxicology: deals with the effects of chemical pollutants in the environment on nonhuman biological organisms, such as fish, birds. 7. Developmental toxicology: is the study of adverse effects on the developing organism that occur any time during the life span of that organism that may result from exposure to chemical or physical agents.  Teratology :is the study of defects induced during development between conception and birth. 8. Reproductive toxicology: is the study of the occurrence of adverse effects on the male or female reproductive system that may result from exposure to chemical or physical agents Classification of toxic agents: Can be classified according to: 1. their target organ : like liver, kidney, hematopoietic system poison. 2. their use: like pesticide, solvents, food additives. 3. their source: like animal and plant toxin 4. their effects: like carcinogens ,mutagens…..etc. 5. their physical state: like gases ,dusts ,metals. 6. their labeling requirements: explosive ,flammable ,oxidizer. 7. their chemistry : aniline derivatives, halogenated hydrocarbons. 8. their poisoning potential: extremely toxic, very toxic. 9. biochemical mechanism of action: sulfhydryl inhibitors.methemoglobin producers. Factors affecting the toxicity of toxic agents: 1. the concentration of the toxic agent, duration & frequency of exposure &route of administration. 2. the chemical &physical properties of the agent. 3. the susceptibility of biologic system or subject. 4. some of the toxicity influencing factors related to person (age, sex , nutritional status ),&the various kinetic factors that influence toxicity (absorption , distribution ,metabolism& excretion)  Route & site of exposure: The major routes by which toxic agents gain access to the body are through:  GIT (ingestion)  Lung (inhalation)  Skin (topical percutaneous, or dermal).  parenteral administration  Toxic agents greatly exhibit the greatest potency &produce the most rapid response when given by intravenous route & an approximate descending order of effectiveness for the other routes would be: inhalation, intraperitoneal , subcutaneous , intramuscular , intradermal ,oral ,&topical. Industrial exposure to toxic agents occurs most frequently by inhalation & topical exposure, while accidental & suicidal poisoning occurs most frequently through oral ingestion.  For many agents the lethal dose for topical exposure is about ten times the lethal dose for oral administration, which in turn is about ten times the lethal dose with intravenous administration. In those situation when the lethal dose for oral or topical administration is close to the lethal dose for IV. Administration it usually means that the toxic agent is absorbed rapidly and easily. Lethal dose (LD50) is the amount of an ingested substance that kills 50 percent of a test sample. It is expressed in mg/kg, or milligrams of substance per kilogram of body weight. o E.g., LD50 for vitamin A is 2000 mg/kg/oral/rat.  Duration & frequency of exposure: Toxic effect may be produced by acute & /or chronic exposure to chemical agents:  acute exposure: is defined as a single exposure or multiple exposure to a chemical occurring within short time (24hrs or less ).  Subacute exposure: refers to repeated exposure to a chemical for 1 month or less.  Subchronic exposure: exposure for 1-3 months.  Chronic exposure: is defined as exposure to a chemical agents for more than 3months.  the frequency of administration is other related factor , in general fractionation of the dose reduces the effect.  a single dose of a test substance that produces an immediate server effect might reduce less than half of the effect when given in two divided doses & no effect when given in ten doses over a period of several hours or days.