Systems of Measurement in Veterinary Pharmacology

Dr. Dipa Brahmbhatt VMD, MS, MPH

ID and convert within and between metric, household and apothecary

Calculate drug dose: tablets/ solutions Calculate solutions Calculate dilutions If time permits: fluid calculations (mostly in

special topics: review)

Refer to the practice problems in the back of chapter 2.

And…

CPTVT: Chapter 2 Dilutions and Solutions handout Medical Mathematics and Dosage Calculations for

Veterinary Professionals◦ CHAPTER 6◦ CHAPTER 8◦ CHAPTER 10

◦ Homework: Dose, Solution, Dilution

◦ What are my advisement times?

Household system: lacks standardization; not accurate for measuring medicine

Metric system: developed in late 18th century to standardize measures and weights for European countries◦ Units based on factors of 10◦ Prefixes denote increases or decreases in size of

unit Apothecary system: system of liquid

units of measure used chiefly by pharmacists

Uses household measures when an approximate dose is acceptable

Uses a system of weights and measures based on 1 pound containing 16 fluid ounces

Calibrated in units that most people are familiar with such as teaspoon and cup

The drop, tablespoon, and teaspoon are the only household measures still used in pharmacology◦ Disinfectants: cups, quarts and gallon

System of liquid measure used by pharmacists; also called the common system

Derived from the British apothecary system of measures

Units in the apothecary system:◦Volume: Minim = liquid volume of a drop

of water from a standard medicine dropper 60 minims = 1 fluid dram 8 fluid dram = 1 ounce

◦Weight: Grain = basic unit of weight measurement 1 grain of wheat = 60 mg. 480 grains = 1 oz = 1 oz , 12 oz = 1 lb

A.k.a. the international system (SI)

Units are based on factors of 10

Base units are meter (length), liter (volume), and gram (weight)

King – kilo (k)- = one thousand units = 1,000 (103) Henry – hecto- = one hundred units = 100 (102) Died – deka- = ten units = 10 (10) L = vol.; Mightily = meter; G = gram = 1 unit = 1 Drinking – deci (d)- = one tenth of unit = 0.1 (10-1) Chocolate – centi (c)- = one hundredth of unit = 0.01 (10-2) Milk – mili (m)- = one thousanth of unit = 0.001 (10-3) More – micro (µ or mc) - = one millionth of unit = 0.000001

(10-6) Naughtily – nano (n) - = one billionth of unit = 0.000000001

(10-9)kg to g = move decimal point 3 places to the rightg to kg = move decimal point 3 place to the left

l to ml = move decimal point 3 places to the rightml to l = move decimal point 3 places to the left

Converting from larger to smaller units – multiply (MORE)Converting from smaller to larger units – divide (LESS)

KNOW TABLE 2-3 pg. 33 Always validate answer.

66 lbs = __________ kg.1 kg = 2.2 lb

X = 66 lbX = (66 lb / 2.2 lb) * 1 kg

= 30 kg

In the Fahrenheit system, water freezes at 32 degrees; water boils at 212 degrees

In the Celsius system, water freezes at 0 degrees; water boils at 100 degrees

Comparison: ◦ 212 – 32 = 180◦ 100 – 0 = 100◦ 180 ÷ 100 = 1.8

C = (F – 32)/1.8C = (F – 32)/1.8F = 1.8C + 32F = 1.8C + 32

98.6 F = ___________ CelsiusDegree Celsius = (Degree Fahrenheit – 32)/1.8

Degree Celsius = (98.6 degree Fahrenheit – 32)/ 1.8 = 37 degree Celsius

Must know correct amount of drug to administer to a patient

Must be in same system of measurement Weight conversion factor: 2.2 lb = 1 kg Remember that drugs can be measured

in mcg, mg, g, gr, ml, l, units Remember that drugs can be dispensed

or administered in tablets, ml, l, capsules

STEP 1: Convert weight into kg (IF DOSAGE mg/kg)◦ 1 kg = 2.2 lbs◦ X = 22 lbs◦ X = (22 lbs/ 2.2lbs) * 1 kg = 10 kg

STEP 2: From dosage to dose◦ Dosage: 2mg/kg◦ Dose: 10kg * 2mg/kg = 20 mg

STEP 3: From dose to amount administered◦20 mg ◦ Tablets: 40 mg, 80 mg and 100 mg

½ of the 40 mg tablet (assuming that tablet is scored!!) ½ tablet – 40 mg

◦ Solution: 10 mg/ ml (20 mg/ 10 mg) * 1 ml = 2 ml 2 ml of 10mg/ml drug solution

STEP 4: Total dose: BID for 7 days Tablet: 7 tablets Solution: 28 ml of the 10mg/ml solution

HOMEWORK 1 DOSAGE DUE TOMORROW

Romich, J.A. Pharmacology for Veterinary Technicians, 2nd edition. 2010.

Bill, R.L. Clinical Pharmacology and Therapeutics for the Veterinary Technician, 3rd edition. 2006.

Bill, R.L. Medical Mathematics and Dosage Calculations for Veterinary Professionals, 2nd edition. 2009.