Increased susceptibility to the action of the drug due to its continued ad- 

 ministration also occurs. It rarely gives trouble except with those drugs 

 such as Digitalis which can be more readily absorbed by the normal body 

 than they can be excreted by it. Disease may readily influence the ab- 

 sorption of a drug on the one hand or interfere with its excretion on the 

 other. For example a large skin-wound may readily absorb a poisonous 

 dose of carbolic acid or iodoform. Or increased acidity in the stomach may 

 lead to a larger absorption of bismuth salts than is normally the case. 

 Diminished excretion by the kidney will lead to a more prolonged action 

 of strychnine. 



Secondly, the doses of the pharmacopoeia are doses for adults. For 

 children much smaller doses must be given. The rule suggested by 

 Young is perhaps the best for calculating the dose for a child. Multi- 

 ply the adult dose by the age of the child and divide by the age of the child 

 plus 12. Thus for a child of three, the dose would be -^j^ or 1 /5th; for 



i *} X ^ 



an adult dose of 15 min. it would be 3+12 or 3 min. Another rule sug- 

 gested by Brunton is to multiply the age at the next birthday by the dose 

 and divide by 25 (the assumed- adult age), or perhaps better multiply the 

 dose by four times the age at the next birthday and divided by 100: for 

 the example stated above that would be j-^p or 2.4 min. roughly 2>^ 

 min. Young children are particularly prone to be affected by morphine 

 and its allied drugs, but are proportionately little influenced by strychnine,, 

 and alcohol. 



Persons above the age of sixty are proportionately more affected by 

 drugs than are younger persons, so that by adults must be understood 

 persons between 20-60 years of age. Persons over 60 should receive 

 roughly $4 and persons over 85 roughly }4 of the adult dose, save in the 

 case of purgatives to which the aged are often very refractory. 



Thirdly, the frequency of repetition makes a great difference in the size 

 of dose to be administered. The more frequently the drug is to be ad- 

 ministered the smaller the dose should be. 



Fourthly, the time of day makes as a rule but little difference; except 

 with the case of drugs meant to bring on or increase a normal daily con- 

 dition. For example a larger dose of a hypnotic such as chloral would be 

 necessary to produce sleep during the day than at night. Also purgatives 

 can best be given at such an hour that they will take effect at the hour of 

 the patient's daily defecation. For this purpose calomel and aloes must 

 be given some eight hours in advance, while purgative salts act within an 

 hour or so. 



The presence or absence of food in the stomach makes a great difference 

 in the rapidity with which drugs are absorbed and in the quantity coming 

 in contact with the wall of the stomach and so irritating it, and as a con- 

 sequence of this larger quantities of any drug irritant to the stomach may 

 be given immediately after than before meals. 



18 



