CHAPTEK VII 

 INTRODUCTION TO PHARMACOLOGY 



ACTION OF DRUGS 



Drugs produce their action in a living organism by either in- 

 creasing, decreasing or stopping one or more functions of the body, 

 and when used in the treatment of disease are almost always used 

 upon this principle. The action or changes produced in a living 

 organism may be of a chemical or physiologico-chemical nature. 

 Most drugs unite with some constituent of the organism and by 

 virtue of this union change its functions. Some, such as the 

 neutral salts, act in great part through their physical relations to the 

 tissues and it is due to this fact that the salines produce purgation by 

 drawing water from the blood into the intestines. 



Local Action. A drug may produce alteration in the function 

 of a part before entering the circulation. These changes may be loss 

 of sensation (Anesthesia), inflammation, etc., with its symptoms of 

 necrosis and astringent effect, in this way constituting what is 

 termed local effect. The changes produced after a drug has entered 

 the circulation are knowu as general or systemic effects. There are 

 a few other terms that should be explained. Remote actions occur- 

 ring in distant parts of the body (may be systemic or indirect). 

 Direct or primary effects are produced by the direct action of the drug 

 on the parts involved. Indirect effects (sometimes called secondary 

 effects) are not produced -by the action of the drug upon the tissue 

 concerned but by the intervention of some other structures on 

 which the drug acts. Immediate effects (also called primary) are 

 the effects resulting at once. Late effects are those occurring later. 

 If preceded by other immediate actions they are properly called 

 secondary actions. 



Factors Which Modify Action of Drugs. The factors which 

 modify the action of drugs are: weight, age, sex, temperament, 

 habits, idiosyncrasy, nature of disease, object of medication, form 

 of remedy, method of administration, time of administration, and 

 frequency of administration. 



1. Body Weight. It is obvious that it would be a good practice 

 to administer a definite dose according to the weight of the animal, 

 as is done in a pharmacological investigation, but it is not convenient 

 to weigh animals in all cases and very difficult to estimate the exact 

 weight. This method has been attempted, taking the weight of the 



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