Dosage Calculations - Ccma

1. A patient is prescribed 20 units of Lantus insulin subcutaneously. The vial is labeled U-100 (100 units/mL). How many milliliters of insulin should be administered?
   Answer: 0.2 mL The correct answer is 0.2 mL. The concentration of U-100 insulin is 100 units per mL. The ordered dose is 20 units. To calculate the volume in mL, divide the ordered units by the concentration: $20 \text{ units} \div 100 \text{ units/mL} = 0.2 \text{ mL}$. While an insulin syringe is calibrated in units for accuracy, it is essential to know the corresponding volume.
2. An order is written for erythromycin 0.5 g PO. The pharmacy dispenses an oral suspension with a concentration of 250 mg per 5 mL. How many milliliters should the patient take per dose?
   Answer: 10 mL The correct answer is 10 mL. First, ensure the units are the same. The order is for 0.5 grams (g) and the supply is in milligrams (mg). Convert the order to mg: $0.5 \text{ g} \times 1000 \text{ mg/g} = 500 \text{ mg}$. Now, use the formula (Dose Ordered / Dose on Hand) × Volume: $(500 \text{ mg} / 250 \text{ mg}) \times 5 \text{ mL} = 2 \times 5 \text{ mL} = 10 \text{ mL}$.
3. A pediatric patient weighing 8 lbs 4 oz needs a weight-based medication. To perform the dosage calculation, the medical assistant must first convert the weight to kilograms. What is the child's weight in kilograms?
   Answer: 3.75 kg The correct answer is 3.75 kg. First, convert the ounces to a decimal fraction of a pound. There are 16 ounces in a pound, so 4 oz is $4 \div 16 = 0.25$ pounds. The total weight in pounds is $8 + 0.25 = 8.25 \text{ lbs}$. Next, convert pounds to kilograms by dividing by 2.2: $8.25 \text{ lbs} \div 2.2 \text{ lbs/kg} \approx 3.75 \text{ kg}$.
4. A provider orders a 250 mg dose of a medication. The stock vial has a concentration of 1 g in 4 mL. How many milliliters should the medical assistant draw up for the injection?
   Answer: 1 mL The correct answer is 1 mL. First, convert the units to be the same. The stock is 1 gram (g), which equals 1000 milligrams (mg). So the concentration is 1000 mg/4 mL. Next, calculate the volume for the 250 mg dose. Using ratio and proportion: $(250 \text{ mg} / 1000 \text{ mg}) \times 4 \text{ mL} = 0.25 \times 4 \text{ mL} = 1 \text{ mL}$. Alternatively, simplify the concentration to 250 mg/mL and see that the ordered dose is exactly 1 mL.
5. A provider orders 7.5 mL of an antacid suspension for a patient. To ensure the patient can measure the dose accurately at home, which of the following instructions is most appropriate for the medical assistant to provide?
   Answer: Take 1 1/2 teaspoons. The correct answer is 1 1/2 teaspoons. The standard medical conversion is $1 \text{ teaspoon (tsp)} = 5 \text{ mL}$ and $1 \text{ tablespoon (tbsp)} = 15 \text{ mL}$. To convert the ordered dose of 7.5 mL to teaspoons, divide by 5: $7.5 \text{ mL} \div 5 \text{ mL/tsp} = 1.5 \text{ tsp}$. One-half tablespoon would be $15 \text{ mL} \div 2 = 7.5 \text{ mL}$, which is also correct, but teaspoons are a more common and smaller unit of measure for this volume, making 1 1/2 teaspoons the most appropriate instruction.
6. A provider prescribes warfarin 7.5 mg PO. The pharmacy supplies 5 mg scored tablets. How many tablets should the medical assistant administer?
   Answer: 1.5 tablets The correct answer is 1.5 tablets. To calculate the number of tablets, divide the prescribed dose by the strength of the available tablets: $7.5 \text{ mg} \div 5 \text{ mg/tablet} = 1.5 \text{ tablets}$. Since the tablets are scored, it is acceptable to administer one and a half tablets to achieve the correct dose.
7. A patient is to receive an injection from a vial containing 400,000 units of penicillin G per mL. The ordered dose is 300,000 units. How many milliliters should be administered?
   Answer: 0.75 mL The correct answer is 0.75 mL. This is a ratio and proportion problem. Use the formula (Dose Ordered / Dose on Hand) × Volume. The ordered dose is 300,000 units. The dose on hand is 400,000 units in 1 mL. Calculation: $(300,000 \text{ units} / 400,000 \text{ units}) \times 1 \text{ mL} = 0.75 \text{ mL}$.
8. A provider prescribes amoxicillin 30 mg/kg/day, to be given in two divided doses, for a child who weighs 44 lbs. The available suspension is 250 mg/5 mL. How many mL should be administered for each dose?
   Answer: 6.0 mL The correct answer is 6.0 mL. First, convert the child's weight from pounds to kilograms: $44 \text{ lbs} \div 2.2 \text{ lbs/kg} = 20 \text{ kg}$. Second, calculate the total daily dose in mg: $30 \text{ mg/kg} \times 20 \text{ kg} = 600 \text{ mg}$. Third, since the dose is divided into two doses, calculate the amount per dose: $600 \text{ mg} \div 2 = 300 \text{ mg}$. Finally, calculate the volume to administer per dose using the available suspension: $(300 \text{ mg} / 250 \text{ mg}) \times 5 \text{ mL} = 1.2 \times 5 \text{ mL} = 6.0 \text{ mL}$.
9. A provider orders a medication dose of 4 mg/kg for a patient who weighs 154 lbs. The medication is supplied in a vial containing 250 mg in 5 mL. What volume in mL should be administered?
   Answer: 5.6 mL The correct answer is 5.6 mL. First, convert the patient's weight from pounds (lbs) to kilograms (kg): $154 \text{ lbs} \div 2.2 \text{ lbs/kg} = 70 \text{ kg}$. Next, calculate the total required dose in mg: $4 \text{ mg/kg} \times 70 \text{ kg} = 280 \text{ mg}$. Finally, calculate the volume to administer from the supplied vial (250 mg/5 mL, which simplifies to 50 mg/mL): $280 \text{ mg} \div 50 \text{ mg/mL} = 5.6 \text{ mL}$.
10. A provider orders 1500 mg of a medication PO. The medication is available in 0.5 g tablets. How many tablets should the medical assistant administer?
    Answer: 3 tablets The correct answer is 3 tablets. First, convert the units to be consistent. The order is in milligrams (mg) and the stock is in grams (g). Convert the stock to mg: $0.5 \text{ g} \times 1000 \text{ mg/g} = 500 \text{ mg}$ per tablet. Then, divide the ordered dose by the dose on hand: $1500 \text{ mg} \div 500 \text{ mg/tablet} = 3 \text{ tablets}$.
11. A patient weighing 176 lbs is prescribed a total daily dose (TDD) of insulin at 0.5 units/kg/day. This TDD is split, with 50% given as basal insulin and 50% as bolus insulin divided equally among three meals. What is the rapid-acting (bolus) insulin dose for a single meal, rounded to the nearest whole number?
    Answer: 7 units The correct answer is 7 units. First, convert weight to kg: $176 \text{ lbs} \div 2.2 \text{ lbs/kg} = 80 \text{ kg}$. Second, calculate the TDD: $0.5 \text{ units/kg} \times 80 \text{ kg} = 40 \text{ units}$. Third, calculate the total bolus dose for the day (50% of TDD): $40 \text{ units} \times 0.50 = 20 \text{ units}$. Finally, divide the total bolus dose by the three meals: $20 \text{ units} \div 3 \approx 6.67 \text{ units}$, which rounds to 7 units per meal.
12. A medical assistant is preparing an injection of Cefazolin 500 mg IM. The medication is in a 1 g powder vial. The instructions state: "Reconstitute with 2.5 mL of sterile water to yield a final concentration of 330 mg/mL." How many milliliters should be drawn into the syringe?
    Answer: 1.5 mL The correct answer is 1.5 mL. The provider ordered 500 mg. After reconstitution, the final concentration is 330 mg/mL. To find the volume, divide the desired dose by the concentration: $500 \text{ mg} \div 330 \text{ mg/mL} \approx 1.515 \text{ mL}$. This is rounded to 1.5 mL for administration. The 1 g and 2.5 mL values are used for reconstitution but are not the final volume to be administered.
13. A provider orders 100 mg of hydrocortisone to be administered IV. The stock vial contains a 2% hydrocortisone solution. How many milliliters of the solution should be drawn up for the injection?
    Answer: 5 mL The correct answer is 5 mL. First, interpret the concentration of a 2% solution. A 2% solution contains 2 grams of solute per 100 mL of solvent. Convert grams to milligrams: $2 \text{ g} = 2000 \text{ mg}$. So, the concentration is 2000 mg/100 mL, which simplifies to 20 mg/mL. Next, calculate the volume needed for a 100 mg dose: $100 \text{ mg} \div 20 \text{ mg/mL} = 5 \text{ mL}$.
14. A pediatrician orders cefdinir 150 mg PO once daily for a child who weighs 33 lbs. The recommended dosage range for cefdinir is 7-14 mg/kg/day. Which of the following is the most appropriate action for the medical assistant?
    Answer: Administer the medication as ordered. The correct answer is to administer the medication as ordered. First, convert the child's weight to kg: $33 \text{ lbs} \div 2.2 \text{ lbs/kg} = 15 \text{ kg}$. Next, calculate the safe dosage range for this child. Low end: $7 \text{ mg/kg} \times 15 \text{ kg} = 105 \text{ mg}$. High end: $14 \text{ mg/kg} \times 15 \text{ kg} = 210 \text{ mg}$. The ordered dose of 150 mg falls within the safe range of 105-210 mg per day. Therefore, the dose is appropriate.
15. A provider prescribes metoprolol 75 mg PO daily for a 68-year-old patient whose blood pressure is 152/94 mm Hg. The pharmacy supplies 50 mg scored tablets. How many tablets should the medical assistant instruct the patient to take per dose?
    Answer: 1.5 tablets The correct answer is 1.5 tablets. The required dose is 75 mg. The available tablets are 50 mg. Using the dosage calculation formula: (Dose Ordered / Dose on Hand) = (75 mg / 50 mg) = 1.5. Since the tablets are scored, they can be safely split in half. The patient's age and blood pressure are extraneous information not needed for this calculation.
16. A medical assistant measures a wound on a patient's leg to be 3.5 inches in length. For documentation in a clinical trial record that requires metric units, what is this length in centimeters (cm)? (Use the conversion $1 \text{ inch} = 2.54 \text{ cm}$)
    Answer: 8.89 cm The correct answer is 8.89 cm. To convert inches to centimeters, multiply the number of inches by the conversion factor 2.54. Calculation: $3.5 \text{ inches} \times 2.54 \text{ cm/inch} = 8.89 \text{ cm}$.
17. A patient is prescribed an ophthalmic solution with instructions to instill 2 drops (gtt) in each eye twice a day. The solution's concentration is 5 mg/mL, and the dropper delivers 20 gtt/mL. How many milligrams of medication is the patient receiving per day?
    Answer: 2 mg The correct answer is 2 mg. First, calculate the total number of drops per day: 2 drops/eye × 2 eyes × 2 times/day = 8 drops/day. Next, determine the volume per day. Since there are 20 drops/mL, the total volume is $8 \text{ drops} \div 20 \text{ drops/mL} = 0.4 \text{ mL}$. Finally, calculate the total mg of medication per day using the concentration of 5 mg/mL: $0.4 \text{ mL} \times 5 \text{ mg/mL} = 2 \text{ mg}$.
18. A medical assistant records a patient's temperature as 38.5 °C during triage. The electronic health record system requires the temperature to be entered in Fahrenheit. What is the equivalent temperature in degrees Fahrenheit (°F)?
    Answer: 101.3 °F The correct answer is 101.3 °F. The formula to convert Celsius to Fahrenheit is $°F = (°C \times 9/5) + 32$. Using the patient's temperature: $°F = (38.5 \times 1.8) + 32$. First, multiply 38.5 by 1.8, which equals 69.3. Then, add 32: $69.3 + 32 = 101.3 °F$.

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