INCOMPATIBILITY. 



Before entering the study of prescription writings it is essential to 

 consider the results of improper combination of drugSj i.e., incompati- 

 bility. 



While a knowledge of chemistry, pharmacy and the physiological 

 actions of drugs is necessary to avoid incompatibility, it is yet possible 

 to formulate certain rules which will assist us in escaping unfortunate 

 combinations. 



Incompatibility is conveniently divided into three classes: I. Chem- 

 ical. II. Physical. III. Physiological. 



I. Chemical incompatibility occurs when drugs are so mixed that an 

 unsuitable alteration in their chemical composition 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, therefore, incom- 

 patible with them. 



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

 acid salts, because decomposition and chemical change will ensue. 



4. A mixture of salts in solution will decompose if either an insolu- 

 ble compound or double salt can be formed; otherwise no change will 

 take place. 



5. Chloral is incompatible with alkaline solutions, because chloro- 

 form is aenerated. 



6. Chloroform and potassium cyanide form prussic acid. 



7. Potassium chlorate, nitrate, or permanganate, liberates oxygen 

 and should not be mixed with readily oxidizable substances, such as char- 

 coal, sugar, sulphur, glycerin, carbolic acid, iodine, turpentine and 

 organic materials, lest explosive compounds be formed. 



8. Lime water precipitates mercury salts. 



9. Both calomel and antipyrine are incompatible with sweet spirit 

 of nitre. 



10. Calomel may not be combined with nitrohydrochloric acid lest 

 corrosive sublimate result. 



11. Calomel and prussic acid form the poisonous mercuric cyanide. 



12. Liquid iron compounds are incompatible with fluid preparations 



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