Chapter 10 and Solution/Dilution Handout

1. Chapter 10 and Solution/Dilution Handout Systems of Measurement in Veterinary Pharmacology Dr. Dipa Brahmbhatt VMD, MS, MPH

2. OBJECTIVES • 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)

3. Practice! Practice! Practice! • 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? 

4. Solutions • 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

5. Working With Solutions • The amount of solute dissolved in solvent is known as the concentration • 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.

6. Rules of Thumb When Working with Solutions • 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)

7. Rules of Thumb When Working with Solutions • 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)

8. Solutions • 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

9. COMPLETE SOLUTIONS HANDOUT • HOMEWORK IS QUESTION 1-16 DUE TOMORROW

10. DILUTIONS

11. Percent Concentration Calculations • Pure drugsare substances that are 100% pure • Stock solutionis 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

12. Another Way to Determine Volume 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

13. Volume concentration method 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

14. Volume concentration method • 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

15. Drug Concentrations in Percents • 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

16. Drug Concentrations in Percents • 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

17. GO THROUGH DILUTIONS HANDOUT • HOMEWORK: pg. 58: 1-8 and pg. 62: 1-4. DUE TOMORROW

18. Reconstitution Problems • 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

21. References • 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.