64 INTRODUCTION TO PHARMACOLOGY 



than emetics, strychnine in larger doses as a stimulant than as a 

 tonic. 



10. Form of medicine. In general, liquids are more active than 

 solids, and alcoholic liquids more than aqueous. Active principles 

 are more soluble than crude drugs, powders and dry filled capsules 

 than pills, uncoated pills than coated ones, and tablet triturates than 

 compressed tablets. 



Besides the above, there are some cathartic drugs which are more 

 active than their active ingredients (aloes, cascara) ; this is probably 

 due to the presence of the extractive matter which retards absorption 

 and keeps the active principles in the alimentary tract until they 

 reach the colon. 



11. Channel of administration. It has been usually considered 

 that the hypodermic dose is half the oral, and that of the rectum 

 twice that of the mouth. However, in a number of instances, drugs 

 are absorbed from the rectum as rapidly as from the stomach, or more 

 quickly even, and some drugs are absorbed from the stomach and 

 duodenum (dogs, at least), with sufficient rapidity to give effect in a 

 short time. The rate of absorption of different drugs from the 

 various channels differs so greatly that no absolute rule can be 

 applied. Furthermore, since these methods of administration are 

 resorted to only on special occasions their amounts should be about 

 the same. In intravenous medication the dose is small because the 

 drugs are injected directly into the circulation. 



12. Time of administration. This is not of any great importance 

 in large animal practice, because the stomachs of herbivora are never 

 empty. In the carnivora and onmivora the action is usually more 

 rapid if given before a meal, because the medicine will not be diluted 

 with the food in the stomach. 



13. Frequency of administration. It is impossible to give any 

 rule for repetition of doses. In general, drugs which produce action 

 very rapidly require frequent doses to maintain their action, while 

 those which act slowly are not often given more than two or three 

 times daily. It is obvious that the dose of a potent drug is less if it 

 is given at frequent intervals than at longer ones. 



METHODS OF ADMINISTRATION 



Orally, subcutaneously or hypodermically, intramuscularly, in- 

 tratracheally, intravenously, inhalation, per rectum, endermic. 



1. Orally, per mouth, per os. This is the most common way of 

 administering medicines. If given for action upon the stomach, 

 drugs should be administered some time before a meal, because the 

 gastric juice may cover the mucosa to such an extent as to interfere 

 with the action of the drug. A very powerful or poisonous medicine 

 should be given during or after a meal, so that the absorption will 



