14 CIRCUMSTANCES MODIFYING THE ACTION OF DRUGS 



Saturated boric acid solution is most often used, or ^jj to % per 

 cent, solution of sodium fluoride. 



Dosage. 



The ptudy of dosage is known as Posology. The action of drugs is 

 altered both in degree and in kind by the dose. Thus, increasing the 

 dose would naturally lead to an increase in the intensity of a drug's 

 action, but it frequently changes the entire character of the action as 

 well. 



Drugs, as strychnine, acting especially on the nervous system, often 

 excite in therapeutic doses, but depress and paralyze in toxic doses. 

 Drugs, as digitalis, stimulating the heart in medicinal doses, usually de- 

 press and paralyze the organ in poisonous doses. Many drugs promoting 

 urinary secretion, in ordinary doses, cause inflammation and urinary 

 depression in large doses. The best way to determine the dose of a drug 

 is to estimate the amount required for each pound of live weight. This 

 applies only to the same species and to animals of ordinary build. Fat 

 is a comparatively inert tissue as far as the action of drugs is concerned, 

 so that a very fat horse, weighing, for example, 1,200 pounds, would be 

 affected in a more pronounced manner by a dose of medicine than would 

 a lean horse of the same weight and taking the same dose. In the case 

 of young animals, and of those either above or under the ordinary size 

 of the adult of any species, the dose should be proportioned — according 

 to weight — to the average dose for the adult animal of that species. 

 Thus, if the average weight of a horse is 1,000 pounds, the dose of any 

 drug for a colt weighing 500 pounds would be half the usual dose for 

 adult horses. In a general way the dose for all animals from birth to a 

 few weeks old (being more susceptible), is one-twentieth of that suitable 

 for the mature animal of the same species ; for yearlings, about one-third 

 of the adult dose. The dose recommended for dogs is commonly the same 

 as that given to man, but this rule does not apply in the case of some 

 powerful drugs (strychnine), where the dose should be adjusted to the 

 weight, i.e., so much per pound, live weight. 



It is impossible to calculate the dose for all domestic animals as 

 based on that for animals of one species, because the differences in an- 

 atomy and physiology modify the actions of drugs in degree and kind, 

 but the dose for sheep is about one-fourth of that for the larger rumi- 

 nants. 



The repetition of a dose is determined to a considerable extent by 

 the duration and rapidity of a drug's action. Agents used for their 

 immediate effect, as those relieving pain and stimulating the circulation 

 and respiration, are repeated frequently till the desired effect is attained. 

 Medicines improving the condition of the digestion, blood and nutrition, 

 as tonics of various kinds, require time for the accomplishment of their 

 mission, and are usually given two or three times daily for a period of 

 some weeks. 



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