INCOMPATIBILITY. 



Before entering upon the study of prescription writing, 

 it is essential to consider the results of improper combina- 

 tion of drugs, i.e.y incompatibility. 



While a knowledge of chemistry, pharmacy and the 

 physiological actions of drugs is necessary to avoid incom- 

 patibility, it is yet possible to formulate certain rules which 

 will assist us in escaping unfortunate combinations. 



Incompatibility is conveniently divided into three 

 classes : I. Chemical. II. Physical. III. Physiological. 



I. Chemical incompatibility occurs when drugs are so 

 mixed that an unsuitable alteration in their chemical com- 

 position takes place. Certain substances should usually be 

 prescribed alone because of the frequency with which 

 chemical changes arise when they are combined with other 

 medicines. These are : 



Lead, silver and zinc salts Mineral acids 



Iodine and iodides Solution of potassa and lime 



Tannic and gallic acids Quinine sulphate 



Liquid iron preparations Hydrocyanic acid 



Corrosive sublimate 



The possibilities of the following combinations must be 

 kept in mind to avoid incompatibility : 



1. Solutions of alkaloids are incompatible with tannic 

 acid, alkalies, alkaline salts, and iodides and bromides, 

 because precipitation occurs, 



2. Glucosides are decomposed by acids and are, there- 

 fore, incompatible with them. 



3. Acids may not be added to alkalies, alkaline salts or 

 vegetable acid salts, because decomposition and chemical 

 change will ensue. 



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