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?

Solutions are mixtures of substances not chemically combined with each other◦ The dissolving substance of a solution is

referred to as the solvent (liquid)◦ The dissolved substance of a solution is referred

to as the solute (solid or particles)◦ Substances that form solutions are called

miscible◦ Substances that do not form solutions are called

immiscible

The amount of solute dissolved in solvent is known as the concentrationconcentration

Concentrations may be expressed as parts (per some amount), weight per volume (w/v), volume per volume (v/v), and weight per weight

Usually reported out as percents or percent solution

Remember that a percent is the parts per the total times 100.

Parts: parts per million (ppm) means 1 mg of solute in a kg (or L) of solvent ◦ % conc. of 1:1000 epinephrine?◦ % conc. = (1/1000)*100 = 0.1%

Liquid in liquid: the percent concentration is the volume per 100 volumes of the total mixture (1 ml/100 ml, 5 oz/ 100 oz)

Solids in solids: the percent concentration is the weight per 100 weights of total mixture(60 mg/100 mg, 4.5 g/ 100 g)

Solids in liquid: the percent concentration is the weight in grams per 100 volume parts in milliliters (dextrose 5% = 5 g/100ml = 5000mg/100ml = 50mg/ml)

How much NaCl needed to make 500mls of 0.9% solution◦X = (0.9g NaCl/ 100 ml) * 500 ml = 4.5 g (4.5 ml density is 1 mg/ml)

Prepare 1L of 4% formaldehyde fixative solution from 37% stock solution◦X = (4%/ 37%) * 1000 = 108 ml of stock solution

◦1000 ml – 108 mls of stock = 892 ml of solvent

COMPLETE SOLUTIONS HANDOUT HOMEWORK IS QUESTION 1-16 DUE

TOMORROW

Pure drugs are substances that are 100% pure Stock solution is a relatively concentrated

solution from which more dilute solutions are made

Ratio-proportion method: one method of determining the amount of pure drug needed to make a solution◦ Amount of drug/amount of finished solution = % of

finished solution/100% (based on a pure drug) Remember that the amount of drug used to

prepare a solution is added to the total volume of the solvent

Volume concentration method: Vs = volume of the beginning or stock

solution Cs = concentration of the beginning or

stock solution Vd = volume of the final solution C d = concentration of the final solution

Vs x Cs = Vd x Cd

Vs x Cs = Vd x Cd

How much water must be added to 1L of 90% alcohol to change it to 40%◦ Vs x Cs = Vd x Cd = 1,000mls x 90% = Vd x 40%◦ Vd = 2250 mL◦ 2250 mL – 1000 mL = 1250 mL

How much 1:25 solution of NaCl is needed to make 3 L of 1:50 solution◦ Convert to %◦ (1/25)*100 = 4%; (1/50) * 100 = 2%◦ Vs x Cs = Vd x Cd = Vs x 4% = 3 L x 2%◦ Vs = 1.5 L

Drug concentrations are sometimes listed in percents

Parts per total = parts (in g) per 100 The front of the vial specifies the

concentration (for example, 2% lidocaine) Use x g/100 ml to determine dose

Drug concentrations are sometimes listed in percents

Parts per total = parts (in g) per 100 The front of the vial specifies the

concentration (for example, 2% lidocaine) Use X g/100 ml to determine dose

◦ Dosage: 3mg/ kg; weight: 15 lb dog; 2% lidocaine◦ (15 lb/ 2.2 lb/kg) * 3mg/kg = 20.45 mg◦ 20.45 mg / 20 mg/ml = 1.02 mL

GO THROUGH DILUTIONS HANDOUT HOMEWORK: pg. 58: 1-8 and pg. 62: 1-4.

DUE TOMORROW

Drug is in powder form because it is not stable when suspended in solution◦ Cefazolin sodium, azithromycin, ampicillin

Such a drug must be reconstituted (liquid must be added to it: sterile water, saline, dextrose)

The label should state how much liquid to add Powder may add to the total final volume of

liquid being reconstituted Label a reconstituted drug with the date

prepared, the concentration, and your initials

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.