PHARMACOLOGY-I, Unit -2, 4th Semester 

 Contents :-

1. Pharmacodynamics:-Principles and mechanisms of drug action. Receptor theories
   and classification of receptors, regulation of receptors. drug receptors interactions
   signal transduction mechanisms, G-protein–coupled receptors, ion channel receptor,
   transmembrane enzyme linked receptors, transmembrane JAK-STAT binding
   receptor and receptors that regulate transcription factors, dose response
   relationship, therapeutic index, combined effects of drugs and factors modifying
   drug action.
2. Adverse drug reactions.
3. Drug interactions (pharmacokinetic and pharmacodynamic)
4. Drug discovery and clinical evaluation of new drugs -Drug discovery phase,
   preclinical evaluation phase, clinical trial phase, phases of clinical trials and
   pharmacovigilance.

Pharmacodynamics is the study of drug effects. It starts with describing what the drugs do, and goes on to explain how they do it. Thus, it attempts to elucidate the complete action-effect sequence and the dose-effect relationship. Modification of the action of one drug by another drug is also an aspect of pharmacodynamics.

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PRINCIPLES OF DRUG ACTION :- 

Drugs (except those gene based) do not impart new functions to any system, organ or cell; they only alter the pace of ongoing activity. However, this alone can have profound medicinal as well as toxicological impact. The basic types of drug action can be broadly classed as:

1. Stimulation It refers to selective enhancement of the level of activity of specialized cells, e.g. adrenaline stimulates heart, pilocarpine stimulates salivary glands. However, excessive stimulation is often followed by depression of that function, e.g. high dose of picrotoxin, a central nervous system (CNS) stimulant, produces convulsions followed by coma and respiratory depression.

2. Depression It means selective diminution of activity of specialized cells, e.g. barbiturates depress CNS, quinidine depresses heart, omeprazole depresses gastric acid secretion. Certain drugs stimulate one type of cells but depress the other, e.g. acetylcholine stimulates intestinal smooth muscle but depresses SA node in heart. Thus, most drugs cannot be simply classed as stimulants or depressants.

3. Irritation This connotes a non selective, often noxious effect and is particularly applied to less specialized cells (epithelium, connective tissue). Strong irritation results in inflammation, corrosion, necrosis and morphological damage. This may result in diminution or loss of function.

4. Replacement This refers to the use of natural metabolites, hormones or their congeners in deficiency states, e.g. levodopa in parkinsonism, insulin in diabetes mellitus, iron in anaemia.