Medicines are not given immediately before or after meals, unless certain conditions urgently demand it; they enter circulation much quicker on an empty stomach and then also produce best local results, whereas a full stomach not only retards absorption, but renders poisons and irritating chemicals less injurious. The system is most resistent in the morning, when larger quantities of hypnotics, etc., are required than at night. The interval of doses depends upon rate of absorption and elimination of each drug, and usually should be sufficiently brief as to prevent the patient coming from under a continued influence until finally desired. Medicines change or modify directly the action only of those organs and tissues with which they come into immediate contact; this action may be simply local, or again general (systemic), and while all have one primary (direct) action, they may also produce indirectly (reflexly) one or more secondary (remote) effects.

The identical drug does not give rise to like results in every person, nor do different specimens of the same drug, when taken in equal quantities, produce the precise effects upon the one individual; for this there are several causes:

1. Age

Age. While the adult dose is about uniform (being based upon the average weight of 150 pounds; 68 Kg.), and holds good between the ages of twenty to sixty, yet that from infancy to majority is variable, and should be computed by the following rules: Dr. Cowling's applies to any age up to and including the twenty-fourth year, and is thus: Divide the age at the next birthday by 24, and that fraction of the adult dose gives the quantity sought - child one year at coming birthday = 1/24 of adult dose; gentian, gr. 30, hence 1/24 of 30 = gr. 1 1/4. Dr. Young's applies to any age up to twelve years, and is thus: Divide the age at the coming birthday by that age plus 12 - child two years at next birthday = 2/2+12=2/14=1/7 of adult dose; cinchona, gr.

40, hence 1/7 of 40 = gr. 5 5/7. Dr. Brunton's applies to metric doses, and is thus: Multiply the adult quantity by the approaching birthday, and that again by 4, then remove the decimal point two places to the left; adult dose of catechu is 1 Gm., and for a child five years old at its next birthday =1. X 5 X 4/100 = .2 Gm.

Very old persons are extremely susceptible to strong or even ordinary medication, all doses having usually to be diminished. Children are very acute to opium and many anodynes, yet tolerate larger quantities of purgatives and a few other drugs (castor oil, calomel, rhubarb, codliver oil, iron, belladonna, ipecac, pilocarpine, squill, arsenic, hydrated chloral) than the rules would indicate.

2. Mode Of Administration

Mode Of Administration. This has much to do with the rate of absorption, hence controls largely the dose. Thus the dose hypoder-mieallv is one-half that by the mouth, or one-fourth that by the rectum, and this difference depends upon the rapidity of absorption - the hypodermic being the quickest, the rectum the slowest; on a full stomach, medicines enter circulation much slower than on an empty one.