PRESCRIPTION WRITING 77 



alent to grams of water when measured in cc's. Unfortunately, this is 

 not the case. Theoretically, medicine should be dispensed by weight in 

 the metric system, but as medicines, when given to patients, are usually 

 measured by bulk, they cannot be dispensed by weight without producing 

 a complication. For example, suppose that we order chloroform in a 

 prescription in the metric system, — 



1^ Chloroformi 30 | 



S. Two teaspoonfuls in ^ater. , 



John Smith. 



thinking we are dispensing 10 grams,* for a teaspoonful holds 6 grams 

 of water. But as chloroform weighs % more than water, we really have 

 ordered 1% X 10= 15 Gm. of chloroform. Therefore, in writing a pre- 

 scription for chloroform with other ingredients, weighed in Gm., we would 

 have to add % of the number of Gm. of chloroform in the prescription 

 to the number previously estimated in order to make the chloroform of 

 the same bulk as other liquids of the density of water. 



In order to avoid reducing substances of density differing from that 

 of water, to terms of equivalency with that of water, it is the custom, 

 and now official, to weigh solids in Gm. and measure liquids in cc. (mil). 

 This is an exact method if the doses of drugs are learned in the same 

 way: i.e., if the doses of solids are learned in Gm. and prescribed in 

 Gm., and the doses of liquids are learned in cc. and prescribed in cc. 

 (now mil). 



In writing prescriptions in the metric system a line is drawn perpen- 

 dicularly across the right-hand side of the blank to indicate the decimal 

 point; multiples of the unit being placed to the left of the line, while 

 fractions are written to the right of the decimal line. In using this sys- 

 tem we are spared the annoyance of special signs and different tables 

 for weights and measures. As matters now stand we must be cognizant 

 of both systems, and be able to convert the old into the new, or vice 

 versa. One dram is equivalent to four grams, 3i. = 4 Gm. Therefore, 

 1 Gm. 1= 31^ or gr. 15. Then gr. i. = 1/15 of 1 Gm. ; or .066 Gm. The 

 equivalent of gr. i is .06 Gm. In order to determine the equivalent of 

 fractions of a grain in grams, we divide .06 by the denominator and multi- 

 ply the result by the numerator of the fraction of a grain. For example: 



gr.%=% of .06 Gm. as .06 Gm.=gr.i. 

 3).06(.02X2'=.64. Therefore, gr.%^=.04 Gm. 

 6 





 Again : to find the equivalent of gr. % in Gm. 

 8).066(.008 X 1 = .008 

 64 



2 



Therefore, gr. % := .008 Gm. 



*For each dose. 



Digitized by Microsoft® 



