16 CIRCUMSTANCES MODIFYING THE ACTION OF DRUGS 



Action of Drugs on Dogs and Pigs as Compared with That on Other 



Animals. 



The action of medicine on dogs and pigs is similar in kind to that 

 observed in man, but the former animals are less sensitive to drugs as a 

 rule, since the dose suitable for a man weighing 160 pounds is appropriate 

 for a dog of 40 pounds weight. As exceptions to this rule, we find that 

 dogs will not bear the human dose of calomel, oil of turpentine, or 

 strychnine. In fact, the ordinary tonic dose of strychnine (gr. 1/30) for 

 man will throw a medium sized dog into convulsions, and may kill a 

 small animal, notwithstanding that this amount is recommended as a suit- 

 able canine dose in veterinary text books. 



Contrariwise, the dog is comparatively insensitive to many drugs 

 powerfully influencing man, — notably morphine, aloes, colocynth and 

 rhubarb. Most cathartics act more quickly on dogs than is the case with 

 the other domestic animals, but saline purgatives are less appropriate in 

 often causing vomiting, and because of their bulk. 



Time of Administration. 



This matter has been alluded to in speaking of the absorption of 

 drugs. Medicines readily undergoing decomposition in the presence of 

 other substances, as iodine and hydriodic acid, should be given on an 

 empty stomach; and likewise all drugs, when a speedy action is desired. 

 Irritants should be administered on a full stomach. 



Habit.- — This circumstance does not have the same importance in 

 veterinary medicine which it possesses in human practice, since we con- 

 trol drug habits in animals. Animals usually become less susceptible to 

 the action of drugs on their repetition, e.g., opium and cathartics. This 

 rule does not hold in the case of drugs having a cumulative action, nor in 

 the repeated use of irritants on the skin, for then their action is strongly 

 intensified^ 



Disease. — The action of drugs is profoundly influenced by disease. 

 It is only possible to enumerate a few examples. Pain is almost an anti- 

 dote to opium, and large repeated doses of the drug, previously innocuous, 

 may, on the sudden cessation of pain, induce poisoning. Opium is also 

 borne in enormous doses in peritonitis. Inflammation and congestion of 

 the digestive organs hinder the absorption of all medicines. A congested 

 condition of the alimentary canal, and even of the respiratory tract in 

 horses, contra-indicate the use of strong purgatives in these animals, 

 since superpurgation may occur. A high temperature alters the action of 

 many drugs. 



Opium is not so efficient as an analgesic in fevers, while anti-pyretics 

 will not lower the temperature in health. Stimulants are not nearly so 

 potent in depressed bodily conditions, and counter-irritants will not pro- 

 duce their characteristic actions on the skin when the circulatory func- 

 tions are at a low ebb. 



Idiosyncrasy. — Individual susceptibility to drugs is infrequent, but 

 unfortunately cannot be anticipated. The writer has seen simple zinc 

 oxide (free from adulteration or impurities) cause a frenzy of irritation 



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