Calculation of Medications Measured in Units, Milliequivalents, and Percentages of Concentration

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Chapter 11

Calculation of Medications Measured in Units, Milliequivalents, and Percentages of Concentration

Pretest

Calculate the following problems. If syringes are included, indicate the volume of medication to be administered on the correct syringe, based on the route of administration, to give the most accurate dose. Show your calculations in all instances. Round to the nearest hundredth, as appropriate.

image 1 A physician orders Acthar Gel 50 units IM stat. The medication on hand has a label reading Acthar Gel 80 units/mL.

image 2 A physician orders heparin sodium 1500 units subcutaneously stat. Use the label provided for calculations.

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image 3 A physician orders 750,000 units of penicillin G IM stat for a male teenager who has pneumonia. Use the following label to calculate this information. The medication is reconstituted to 500,000 units/mL.

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image 4 A physician orders penicillin G potassium 500,000 units IM for an adult. Add 1.8 mL of sterile water and use the label provided to answer questions.

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image 5 A physician orders potassium chloride 2 mEq to be added to IV fluids for a patient in electrolyte imbalance. Using the following label, calculate the necessary dose.

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image 6 A physician orders 500,000 units of penicillin G IM stat and q6h. The available medication is penicillin G 250,000 units/mL in a 10-mL vial.

image 7 A physician orders 2500 units of heparin sodium subcutaneously. The medication available is 10,000 units/mL in a 1 mL vial.

image 8 A physician orders Humulin R 50 units in IV fluids to make an insulin infusion.

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image 9 A physician orders Humulin R 35 units subcutaneously stat. The available medication is shown on the previous label.

image 10 A physician orders procaine penicillin G 1,000,000 units IM. The medication available is a 10-mL vial of procaine penicillin G 250,000 units/mL.

image 11 A physician orders Lantus insulin glargine 55 units subcutaneously to be given daily at bedtime. The medication available is shown on the following label.

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image 12 A physician orders 17,000 units of heparin sodium subcutaneously as a stat dose. The available medications are shown on the following labels.

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image 13 A physician orders heparin sodium 750 units subcutaneously as a stat dose. Available are the following labels for preparing the medication for the order.

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image 14 A physician orders a heparin sodium flush 45 units to be administered q12h to keep an intravenous site patent. The available medications are shown on the following labels.

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image 15 A physician orders penicillin G potassium 10,000,000 units to be given IV stat. Use the following label to complete this order.

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image 16 A physician orders V-Cillin K suspension 300,000 units q6h. The available medication is V-Cillin K suspension 200,000 units/5 mL.

image 17 A physician orders Mycostatin oral suspension 250,000 units to be swished and swallowed. The medication is available as shown in the following label.

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image 18 A physician orders Kaon-Cl 40 mEq po qam. The available medication is Kaon-Cl 40 mEq/15 mL.

image 19 A physician orders Klor-Con (KCl) 10 mEq daily. The available medication is Klor-Con 20 mEq scored tablet.

image 20 A physician provides a new prescription for Humulin R 12 units and Humulin N 35 units subcutaneously qam. Use the following labels to calculate the medication for this order.

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Introduction

Medications such as penicillin, insulin, and heparin are measured in International units. With these parenteral medications, the labels read a specific number of units per milliliter. The unit amounts are not interchangeable between types of medications; rather, each medication unit is specific to the drug ordered and represents a standard amount of that particular medication that produces the desired biologic effect.

Milliequivalents are measurements of the strength of ion concentration in a medication indicating the number of grams of solute (usually electrolytes in pharmacology) dissolved in a milliliter of solution or the chemical combining power of the substance.

Percentages are the concentration of weight of a substance or medication dissolved in a solute, either by volume with liquids or weight with solids. (To review how to change a percentage to whole or decimal numbers see Chapter 2.) These medications have the label showing the percentage strength such as Lidocaine 1% or epinephrine 0.1%. Solutions expressed in ratio strengths provide information concerning the ratio of medication to the amount of solute.

Medications expressed as ratio and percentage also show the total active ingredient amount, usually in the metric system on the label. As with unit measures per milliliter, percentages, ratios, and milliequivalents are expressed to indicate the amount of medication per volume amount.

Calculating Dosages in Unit and Milliequivalent Measurements

A unit measurement gives the information concerning the strength of medication in a given drug form, such as volume for liquid. A conversion factor is not necessary because the unit is the factor specific to the strength of the particular medicine. Drugs commonly measured in unit measurements include penicillin, insulin, and heparin. Other less-used medications that have unit measurements are fat-soluble vitamin E, some forms of vitamins A and D, and the topical antibiotic bacitracin. The medication label provides information on the strength of the medication such as insulin U-100 (100 units/mL) or penicillin 500,000 units/mL as an example. These are similar to the medication strengths found with the metric system when mg/mL is used for measurements. Most important for you as a pharmacy technician is the need to be aware of the volume of the medication and strength for the dose as listed on medication labels. As with medication calculations in previous chapters, reading a drug label accurately is of utmost importance and is the basis for correct administration of medications to patients.

Calculating Antibiotics Measured in Units

Penicillins G and V are products measured in the unit system, as are other antimicrobials such as nystatin suspension. In many cases, these medications are available in a powdered form that requires reconstitution before administration. The information on the drug label will inform you about the type and amount of needed diluent. If the label does not specify the needed diluent, in most cases the diluent will be provided with the powdered medication. In some cases the label also provides different strengths for the medication that can be prepared by the amount of diluent added (Figure 11-1). If you need to review the necessary steps for reconstitution of medications, see Chapter 9.

Practice Problems A

Calculate the following problems and if reconstitution is necessary, decide on the amount of diluent that would best provide the dose ordered with the least volume of medication per dose, whether for injection or oral administration. Use ratio and proportion or formula method for calculations. Show your calculations. Round your final answers to the hundredth unless the question asks for a measurable dose.

1. imageA physician orders penicillin G potassium 750,000 units to be added to IV fluids for a postoperative patient. The following label is the medication available for use for administration.

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2. imageA physician orders Pfizerpen 800,000 units to be added to IV fluids. Use the label in Problem No. 1 for calculation.

3. imageA patient with severe bronchitis has an order for penicillin V 250,000 units qid. The medication on hand is oral penicillin V 400,000 units/5 mL.

4. imageA physician orders V-Cillin K tablets 800,000 units to be given bid. The available medication is V-Cillin K 400,000-unit tablets.

5. imageA physician orders penicillin G 450,000 units IM daily for 4 days. The available medication is penicillin G 300,000 units/mL.

6. imageA physician orders penicillin G 750,000 units IM q12h for a patient with a severe bacterial infection. The available medication is penicillin G 300,000 units/mL.

7. imageA physician orders penicillin G 500,000 units IM q6h. The label reads 1,000,000 units/vial.

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8. imageA physician orders Mycostatin Oral Suspension 300,000 units to be administered bid in divided doses for each side of mouth. The available medication is shown on the following label.

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9. imageA physician orders penicillin V oral suspension 200,000 units po qid. The medication available is penicillin V oral suspension 400,000 units/5 mL.

10. imageA physician orders penicillin G procaine suspension 600,000 units IM bid for a patient with a severe infection. The available medication is shown on the following label.

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11. imageA physician orders Bicillin L-A 425,000 units IM. The available medication is found on the following label.

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12. imageA physician orders penicillin G potassium 450,000 units IM as a stat dose. The available medication is on the following label.

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13. imageA physician orders penicillin G 300,000 units IM. A medication vial containing penicillin G 5,000,000 units is available. Directions for reconstitution state to add 8 mL of sterile water to provide a 500,000 units/mL medication.

14. imageA physician orders penicillin G potassium 125,000 units q6h. The vial contains penicillin G potassium 1,000,000 units. The reconstituted strength is penicillin G potassium 250,000 units/mL.

15. imageA physician orders penicillin G potassium 50,000 units/kg/d in two divided doses for a patient who weighs 220 lb. The available medication is penicillin G potassium 2,000,000 units/mL.

16. imageA physician orders penicillin G benzathine 2,400,000 units IM stat for syphilis. The available medication label reads penicillin G benzathine 600,000 units/mL.

17. imageA physician orders penicillin G IV for severe strep throat for a 66-lb child to prevent strep pneumonia. The normal dose is 150,000 units/kg/day in four divided doses.

18. imageA physician orders Mycostatin 200,000 units at bedtime vaginally for a patient with a Candida infection. The available medication is labeled Mycostatin Vaginal Suppositories 100,000 units.

19. imageA patient is being given prophylactic treatment for rheumatic fever. The physician orders penicillin G benzathine 1,200,000 units qmo for this patient. The medication is available as penicillin G benzathine 300,000 units/mL for IM administration.

20. imageMrs. Jones, an elderly patient, has chronic sinusitis. The physician orders penicillin V 300,000 units po qid. The available medication is penicillin V 400,000 units/5 mL.

Calculating Insulin Doses in Units

Insulin, which is used to control type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) in some persons whose elevated blood sugar cannot be adequately controlled with oral hypoglycemics, is prescribed and measured in units. Most insulin preparations are only available in U-100 strength, meaning that each milliliter of insulin contains 100 units of medication. Even insulin preparations that are combinations of regular insulin and intermediate-acting insulins are in U-100 specifications. See Figure 11-2 for labels for different insulin preparations.

To administer insulin preparations, insulin syringes that are calibrated in 100 units/mL must be used; no other syringe is based in units for insulin (in an emergency a tuberculin syringe could be used because it is also calculated in hundredths of milliliters). The design of the syringe makes it easy to ensure that the exact dose of medication ordered is administered. Syringes come in 30-, 50, and 100-unit calibrations (Figure 11-3

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