PHARMACOLOGY

 TOXICOLOGY PRE-CLINICAL TOXICITY AND CLINICAL TRIALS ::

Toxicology is the branch of science dealing with the adverse effects of drugs and study of poisons of living organisms Poisons are the substances which are harmful dangerous or fatal to the living organism As such it is difficult to differentiate a drug and poison since any drug may be poisonous if not used properly or in such doses as to endanger health and life Adverse reaction to drug is a response to a drug which is noxious and unintended and which occurs at doses used in man for prophylaxis diagnosis or therapy 

SIDE EFFECTS AND TOXIC EFFECTS ::

When a drug is used in therapeutic dose it may manifest some unwanted actions simultaneously these are called side effects The unwanted or adverse effects produced at higher doses are called toxic effects Toxic manifestations produce functional disturbances and organic damage far more greater and serious than those of side effects Side effects are less serious as compared to toxic effects They demand stopage of the drug Excess of morphine producing Cheyne -Stokes Breathing results in toxicity of morphine but constipation and miosis (Constriction of pupils) produced by morphine are side effects of this drug Belladonna group when used as spasmolytics may produce dryness of the mouth which is a side effect but if it produces busy delirium by its central action it is toxic effect 

            Organic damage often occurs when toxicity is produced Prolonged use of streptomycin for example may produce vertigo and deafness due to damage of the auditory nerve branches Sometimes mercurials used as diuretics produce nephritis and antitubercular drugs like PAS may damage the liver cells Chloramphenicol on prolonged use is known to produce aplastic anaemia which is of serious consequences