(b) Weight:
1 grain (gr) = 60 mg
1 oz = 30 gm
2.2 lbs = 1 kg
1000 gm = 1 kg
(3) It is important to understand that the apothecary system is only
approximately equivalent to the metric system and to the common household system.
(4) In the apothecary system, fractions and Roman numerals are commonly
used to designate numbers. Morphine, for example, may be ordered as 1/4, 1/6, or 1/8
grain. In addition, atropine may be ordered as 1/150 grain or 1/200 grain.
(5) Roman numerals may or may not be capitalized and are often used in
combination with "SS", which indicates 1/2. Therefore, the term ISS means 1 1/2, and
iiss means 2 1/2.
c. Household Measure.
Approximate equivalents to household measure:
1 teaspoon (tsp) = 5 ml
1 tablespoon (tbsp) = 15 ml = 1/2 oz
3 teaspoons (tsp) = 1 tbsp
2 tablespoon (tbsp) = 30 ml = 1 oz
d. Conversion Between Apothecaries' and Metric Systems.
(1)
Essential equivalents must be learned in order to convert between these
two systems.
(2)
Ratio and proportion is the easiest way to carry out these conversions.
(3)
EXAMPLES:
(a) 45 mg = X gr
60 mg = 45 mg
1 gr
X gr
60X = 45
X = 3/4 gr
MD0904
2-13