CHAPTER IV. 

 INCOMPATIBILITY. 



Many of the drugs and preparations of the materia medica may be 

 and are given alone, but many others only in combination. There are a few 

 which are never or almost never given in combination with other drugs, but 

 the majority of drugs and their preparations are at times given in combin- 

 ations, which are often very complex. The selection of drugs and pre- 

 parations to be used in combination with each other requires a great deal 

 of care to avoid unwished for changes being brought about by thier ad- 

 mixture. Two drugs are said to be "INCOMPATIBLE," when on being 

 brought into intimate contact with each other unwished for changes either 

 physical or chemical are brought about or when their pharmacological 

 actions would so interfere with each other as to be detrimental. It is by 

 no means an infrequent occurrence for a physician to prescribe together two 

 medicines which have almost opposite pharmacological actions but he 

 does so in such proportions that the action of the one serves but to correct 

 some undesired action of the other. 



Incompatibility dependent upon the differing pharmacological actions 

 of the drugs administered together is known as THERAPEUTICAL or better 

 PHARMACOLOGICAL INCOMPATIBILITY. An extreme example would be 

 the administration of atropine and pilocarpine together. 



Incompatibility dependent upon chemical and physical changes can 

 only occur when the drugs are brought into intimate physical contact either 

 by trituration in a mortar (the cases in which incompatibility is apt to 

 make be made manifest in this way will be found mentioned in paragraphs 

 IVd. and V.) or by solution. The incompatibility due to chemical changes 

 occuring between preparations dispensed together is known as CHEMICAL 

 INCOMPATIBILITY. The changes may be of several types and may be classi- 

 fied as follows: 



I. Resulting in chemical change without any visible change. 



(a) The neutralization of acids by bases.* 



(b) The breaking up of glucosides by acids (sugar is set free and the glu- 

 coside loses in activity). 



(c} The action of acids on the activity of pancreatic ferments and of al- 

 kali on gastric ferments. 



2. Resulting in precipitation of newly formed chemical substances due 

 to the interaction of two other chemical substances in solution. 



* Important cases are printed in italics. 



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