metrology

Metrology

It is the science of weights and measures.

Metrology

Types of systems

Two systems of designating weights and measures of drugs and preparations are:
Old apothecaries system.
Classical Metric system.

Although the older apothecary measures may still be used by some clinicians for some drugs, the metric system is now standard.

Old apothecaries system:

This system is used by older prescribers, it is basic unit is grain.
The apothecaries' system of weights is a historical system of mass units that were used by physicians and apothecaries for medical recipes, and also sometimes by scientists.
Types of systems

equivalent

abbreviation
Name
-----
gr
Grain
60 grains
dr
Drachm
8 dr
oz
ounce
12 oz
Ib
pound
Grain : is defined as the weight of a grain of wheat and it is equivalent to 0.06 gm (60 mg).
A . Units of weights:

Equivalent

Abbreviation
Name
---------
---------
Minims
60 minims
Fl.dr
Fluid drachm
8 fl.dr
Fl.oz
Fluid ounce
16.fl.oz
o
pint
Minim(m): is defined as the volume corresponding to 0.06 ml (1 drop).
Or :The minim (abbreviated min, ♏ or ) is a unit of volume measurement. Specifically it is 1⁄60 of a fluidram or 1⁄480 of a fluid ounce
b. Units for measuring
VOLUME


It is very simple because it is standarized system & the difference between one unit &other is tenth, therefore it named Decimal system.
Metric system
(international system)
1/1000000
1/1000
1/100
1/10
unit
10
100
1000
One
million
One
thousand
One
hundred
One tenth

tenth

hundred
thousand
Micro
µ
Milli
o.oo1
Centi
0.01
Deci
0.1
Gram
(gm)
Liter(l)
Meter(m)
Deca
Hecta
kilo


Liter(The litre (International spelling) or liter (American spelling)): it is the volume of 1 kg of water at 4 degree centegrate.
or : a metric unit of capacity, formerly defined as the volume of 1 kilogram of water under standard conditions, now equal to 1,000 cubic centimeters (about 1.75 pints).

Gram: it is the weight of one (ml)

Or defined as "the absolute weight of a volume of pure water equal to the cube of the hundredth part of a metre, and at the temperature of melting ice (later 4 °C),

Conversion from apothecaries system to metric system:

A. units of weights
G 0.06 gm (0.06479891 grams )
Dr. 4 gms
0z 30 gms
B. Units of liquid
m 0.06 ml
Fl.dr 4 ml
Fl.oz 30 ml
0 500 ml

A. units for weight

gm 15 gr(15.4323583529 grains)
kg 2.2 Ib


B. Units for volume of liquids
ml 15 M
L 2 0(Pint)

Conversion from metric system to apothecaries system

Household measures
Household measures are commonly encountered when liquid
preparations are prescribed. If the directions call for the patient to take
a certain volume of drug solution, the pharmacist converts the metric
value given into its household equivalent

1 minim₌ 0.06 ml

Drop
1 ml
20 drop
2.5 ml
Tea spoonful (small)
5 ml
Tea spoonful (large)
15 ml
Table spoonful
30 ml
Coffee cupful
150 ml
Tea cupful
250 ml
glassful
Household measures
(domestic measures)


Calculating the appropriate patient dose, calculating the amount of drug product needed to achieve this dose, expressing the dose in a household measure, and calculating the total amount of the drug to be dispensed by the pharmacist for the full course of treatment are common calculations performed in the practice of dentistry.
Suchcalculations are required when prescribing an antibiotic suspension for a child. Although the mathematics is simple, teaching experience indicates that 40% of students are unable to perform calculations correctly on examination. The 1999 Institute of Medicine report on medical error noted that dosing errors are frequently made in children’s dosing. Students should practice performing such calculations, and any time drug doses are calculated for a patient, they should be double-checked for accuracy.

If a cough syrup contains 0.3 g of drug in 100 ml, how many milligram are contained in each TABLE spoonful dose???
Conversion to apothecaries system???

0.3 100 ml

X 15