INCOMPATIBILITY 69 



of the vegetable bitters (except those of calumba and quassia), because 

 the tannic acid in them throws down a precipitate. 



13. Considerable quantities of acid are incompatible with tinctures, 

 since ethers are' produced. 



14. Water precipitates resinous tinctures. 



15. Gum arabic is incompatible with lead and iron salts, and min- 

 eral acids. 



16. Strychnine is precipitated in solution by potassium bromide. 



17. Pepsin and pancreatin are mutually destructive in fluid com- 

 bination. 



18. Solutions of potassium chlorate and iodide unite to form a 

 poisonous compound. 



It is beyond our scope to attempt the enumeration of all possible 

 drug-incompatibilities. The special incompatibilities of each drug may be 

 found under the proper heading in the detailed description of them. Fur- 

 thermore, we may avoid incompatibility by (above all) simplicity in 

 prescription writing, i.e., the use of a few drugs in combination. Water 

 or alcohol are generally the best solvents. 



II. Physical incompatibility consists in the production of unsightly- 

 looking mixtures, but without necessarily causing any chemical alteration 

 of their ingredients ; for example, the addition of water to insoluble pow- 

 ders, oils and chloroform. While such combinations are pharmaceutically 

 improper, they may sometimes be used to advantage in practice. 



III. Physiological incompatibility consists in the union of drugs 

 possessing antagonistic physiological actions. For instance, the com- 

 bination of purgatives and astringents ; of morphine and atropine ; of 

 digitalis and nitroglycerin. Such prescriptions may be valuable therapeu- 

 tically when the antagonism is not complete. This follows because, while 

 deleterious action of one drug may be offset by another, its beneficial 

 effect may at the same time exist or be accentuated. Thus the anodyne 

 influence of morphine is increased by combination with atropine, but both 

 the depressing action of morphine on the respiration and its constipating 

 tendencies are lessened by atropine. 



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