1. Animal, Plant & Soil Science Lesson C5-5 Veterinary Math

2. Interest Approach Bring in empty bottles, boxes, or labels of common household medications, such as acetaminophen (Tylenol®), acetylsalicylic acid (aspirin), and naproxen (Aleve®). Ask the students to examine the information on these and read dosage amounts, instructions, and side effects of the medications. Facilitate a discussion about the medications, possibly covering the following topics:

3. Interest Approach What is the importance of using the correct dosage? Explain that more medication than the recommended dosage is not better. Why are certain medications provided in different dosages per tablet? What can happen when too much or too little of a drug is used? What are the problems associated with the habitual use of a drug? How are liquid medications measured differently from solid/tablet medications? Why is double-checking measurements and math calculations for medicines important? What are side effects, and how do they relate to too little or too large a dose? What people deal with dosage and concentration frequently in their daily work tasks?

4. Objectives Define dose, dosage, and concentration. Complete conversions necessary to formulate dosages (kg to lb., mg to cc), and calculate appropriate dosages (tablet and liquid) based on body weight.

5. Objectives Read graduated cylinders and syringes, and fill them with correct amounts of medication.

6. Terms concentration dosage dose meniscus therapeutic

7. What are dose, dosage, and concentration? Dose, dosage, and concentration A. A dose is a specified quantity of a therapeutic agent, such as a drug, prescribed to be taken at one time or at certain intervals. Therapeutic means pertaining to a disease treatment or cure.

8. What are dose, dosage, and concentration? B. Dosage is the amount of a drug to be administered per quantity of body weight, usually given in mg/kg (less frequently in mg/lb.). C. Concentration is the strength of a solution—the number of molecules of a substance in a given volume, usually stated in mg/ml or mg/cc.

9. How are measurements converted and dosages calculated? Performing conversions and calculating dosages A. Conversions 1. Unit conversions are necessary to transition between units of measurement. 2. Generally, the initial amount of measurement is written first from left to right. By multiplying the initial amount times the units of the desired amount, the final unit of measurement can be obtained.

10. How are measurements converted and dosages calculated? 3. An equivalent of measurement (e.g., 1 oz. = 28.35 g) should be expressed as a fraction, with the desired resulting unit of measurement written on top and the unit of measurement of the initial amount written on the bottom.

11. How are measurements converted and dosages calculated? 4. The units written on both the top and the bottom will essentially “cancel,” and the last unit on the top right will remain. This unit should be the desired unit for conversion. 5. Example: Convert 2,000 lb. to g (1 lb. = 453.59 g).

12. How are measurements converted and dosages calculated? B. Dosage calculations 1. Tablet a. Often the dosage, or the strength of medication prescribed, is not the same as the strength of medication available. For the appropriate amount of medicine, the correct dosage must be calculated. A tablet of medication may need to be cut in half to give the correct dosage. Some tablets are scored to make halving easier.

13. How are measurements converted and dosages calculated? b. To obtain the correct dosage, divide the strength of the desired dose by the strength of the medicine on hand, and multiply by the quantity of the on hand dose.

14. How are measurements converted and dosages calculated? c. Example: If a dosage of 250 mg of acetaminophen has been ordered, and there are only 500 mg tablets (1 tablet = 500 mg), then the medical care giver needs to provide only half a tablet to equal the correct dosage.

15. How are measurements converted and dosages calculated? 2. Liquid a. Dosage × Weight = Dose in mg (the precise amount of the drug that the animal should receive). b. The unit of weight and the unit of dosage must be the same.

16. How are measurements converted and dosages calculated? c. Example: A guinea pig weighing 900 g needs ivermectin at 0.4 mg/kg. First, 900 g should be converted to 0.9 kg to match the lower unit of the dosage measurement. Then, these numbers should simply be plugged into the formula to determine the dose in mg.

17. How are measurements converted and dosages calculated? d. To determine the dose in cc, the formula to be used is Dose (mg) ÷ Suspension (mg/cc) = Dose (cc) (the precise amount of the suspension containing the correct amount of the drug in mg).

18. How are measurements converted and dosages calculated? e. Example: Ivermectin 1% solution has 10mg/mL (i.e., 10 mg/cc). The dose in cc for the 900-g guinea pig needing 0.4 mg of ivermectin is calculated as follows: f. Calculations should always be double- checked.

19. How are graduated cylinders and syringes read and filled with correct amounts of medication? Correctly reading and filling containers with medication A. Graduated cylinders 1. The volume contained in a graduated cylinder is determined by reading, at eye level, the measurement of liquid at the meniscus, with the cylinder resting on a flat surface.

20. How are graduated cylinders and syringes read and filled with correct amounts of medication? 2. The meniscus is the curved top of a column of liquid in a small tube. It is created because the attractive forces of the liquid’s molecules with the cylinder are stronger than the cohesive forces between the individual liquid molecules. With water, the curve is concave, sagging downward in the middle, whereas with other liquids, such as mercury, it is convex, bulging upward.

21. How are graduated cylinders and syringes read and filled with correct amounts of medication? B. Syringes 1. Give students the following directions for filling a syringe. a. Start with the plunger pushed fully down. b. Insert the needle point into the rubber cap of the vial of medication and hold the syringe with the needle pointed toward the ceiling.

22. How are graduated cylinders and syringes read and filled with correct amounts of medication? c. Begin to fill the syringe with slightly more medication than is needed by gently pulling back the plunger. d. After filling the syringe with more than enough medication, push the excess out by pushing the plunger back in. This will also help remove any air bubbles that may have been drawn up into the syringe from the vial.

23. How are graduated cylinders and syringes read and filled with correct amounts of medication? e. Determine how much medication is in the syringe by measuring from the bottom of the plunger down toward the needle.

24. Review What are dose, dosage, and concentration? How are measurements converted and dosages calculated? How are graduated cylinders and syringes read and filled with correct amounts of medication?