Calculation of Medications Measured in Units, Milliequivalents, and Percentages of Concentration
• Calculate doses of antibiotic medications measured in units
• Calculate insulin doses measured in units
• Calculate anticoagulant doses measured in units
• Calculate medications measured in milliequivalents
• Interpret dosage when the medication is expressed as a percentage
• Interpret dosage of solutions expressed in ratio strength
• Calculate weight of active ingredients expressed in percentage or ratio and proportion
One thousandth of a chemical equivalent; represents the number of grams of solute (usually electrolytes in pharmacology) dissolved in a milliliter of solution or the chemical combining power of the substance
Basic measurement used to indicate the strength of some medications; the unit describes a standardly agreed upon amount of an individual drug that can produce a given biological effect and is specific to that drug alone. The units of one substance are not equivalent to the same number of units of another substance.
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.
1 A physician orders Acthar Gel 50 units IM stat. The medication on hand has a label reading Acthar Gel 80 units/mL.
What measureable volume of medication should be given to the patient? ____________________
What type of syringe should be used to administer this medication? ____________________
Interpret the physician’s order. ______________________________________________________
2 A physician orders heparin sodium 1500 units subcutaneously stat. Use the label provided for calculations.
Interpret the medication order. ______________________________________________________
What is the measurable volume of medication that should be given to the patient? ____________________
What type and size of syringe should be used to prepare this medication? ____________________
What is the total volume of medication in the vial? ____________________
What is the total strength of heparin in the vial? ____________________
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.
What volume of medication should be given to the teen? ____________________
What is the recommended route of administration? ____________________
What is the volume of diluent that was added to the vial? ________________
How long would the medication be potent after reconstitution? _________________
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.
What is the strength of medication per milliliter? _______________________
What volume of medication should be administered to the patient? _______________________
What total volume of medication is in the vial after reconstitution? _______________________
What type of syringe should be used to administer the medication? _______________________
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.
What volume of medication should be added to the IV fluids for this patient? _______________________
What is the milliequivalent per milliliter in this vial? _______________________
What is the total volume of medication of the vial? ________________
What is the total strength of medication in the vial? _______________
How many doses of medication are in this vial if the patient receives the same amount of medication for each dose? _______________________
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.
Interpret the order. __________________________________________________________________
What volume of medication should be administered to the patient with each dose? _________________________
What is the total strength of the medication in the vial? __________
How many doses of medication can be administered from a single vial if the dosage remains the same? _______________________
7 A physician orders 2500 units of heparin sodium subcutaneously. The medication available is 10,000 units/mL in a 1 mL vial.
What volume of medication would the patient receive? _______________________
What volume of medication would be available in the vial after this dose has been prepared? ______________________
Which syringe should be used to provide the most accurate dose of medication? _______________________
Indicate the dose that would be drawn for this order.
8 A physician orders Humulin R 50 units in IV fluids to make an insulin infusion.
Using an unopened vial of medications, what volume of medication should be added to the fluids? _____________
What volume of medication would be available in the vial after the dose of insulin has been prepared? __________________________
Choose the syringe that would provide the most accurate dose of medication and indicate the desired volume.
9 A physician orders Humulin R 35 units subcutaneously stat. The available medication is shown on the previous label.
What volume of medication should be prepared to meet the order? ____________
Which syringe would you choose to provide the most accurate dose to administer this medication? _______________________
Indicate the dose that would be drawn for this order.
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.
What volume of medication should be given for this order? _______________________
Which syringe should you choose for the order? _______________________
What is the total concentration of the medication in the vial? ___________________
Indicate the volume of medication on the correct syringe.
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.
Can this medication be mixed with other insulin preparations? ____________________
Indicate on the syringe the amount of medication that should be shown to the patient for appropriate administration at home.
12 A physician orders 17,000 units of heparin sodium subcutaneously as a stat dose. The available medications are shown on the following labels.
Which label strength of medication would be optimal to prepare the medication order? _______________________
What volume of medication should the patient receive when using the selected vial of medication? _______________________
Which syringe would be appropriate for administration of the medication? _______________________
Indicate the amount of medication on the appropriate syringe.
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.
Which vial of medication should be made available for administration? _______________________
Which syringe should be used for administration? _______________________
Indicate the amount of medication on the correct syringe.
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.
Choose the appropriate medication for completing the order. _______________________
What volume of medication should be administered to the patient using the appropriate medication label? _______________________
Indicate the correct amount of medication to be administered to prepare this order on the correct syringe.
15 A physician orders penicillin G potassium 10,000,000 units to be given IV stat. Use the following label to complete this order.
If 11.5 mL of diluent is added to this vial, what is the strength of the medication per milliliter? _______________________
For what length of time would the medication be acceptable for use after reconstitution? _______________________
What volume of medication should be added to IV fluids to complete this order as diluted above? _______________________
Indicate the needed documentation for the label following reconstitution using today’s date and time and initials as appropriate. ____________________
Choose the appropriate syringe that is necessary to add the penicillin to the fluids.
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.
What volume of medication should be administered? _______________________
On the following measuring device(s), show the volume of medication that should be administered.
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.
What volume of medication should be administered? _______________________
Which oral measuring device(s) could be used to administer this medication? _______________________
Indicate the amount to be administered on the correct measuring device(s).
18 A physician orders Kaon-Cl 40 mEq po qam. The available medication is Kaon-Cl 40 mEq/15 mL.
What volume of medication should be administered? _______________________
Which measuring device(s) should be used to administer this medication? _______________________
How could this be administered using a household measuring device? ______________
Indicate the amount to be administered on the correct utensil.
19 A physician orders Klor-Con (KCl) 10 mEq daily. The available medication is Klor-Con 20 mEq scored tablet.
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.
How many units of medication would be available in each vial for future use when this dose of medication has been prepared? ________________
Using the syringes that follow, show the amount of regular insulin on one syringe, the amount of Lente insulin on another syringe, and the total amount of insulin on the final syringe.
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.
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. 
A 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.
What volume of diluent should be added to the medication for the strength to be 500,000 units/mL? ____________________
What volume of medication should be added to the IV fluids? _______________________
What volume of medication would be left in the vial after medication is prepared? _______________________
Should the residual medication be diluted to another dosage strength? _______________________ Explain your answer ____________________
Which syringe for injection should be used to prepare the medication for addition to IV fluids? _______________________
2. 
A physician orders Pfizerpen 800,000 units to be added to IV fluids. Use the label in Problem No. 1 for calculation.
What amount of diluent is added to the vial for medication strength of 250,000 units/mL? _______________________
What volume of medication should be prepared for a patient dose? _______________________
What volume of medication would remain in the vial following preparation of the ordered medication? _______________________
Show the documentation that would be needed on the vial, using today’s date and time as guide if necessary. _______________________
How long would the medication be stable in the vial following reconstitution? _______________________
Which syringe should be used to add the medication to the IV fluids? _______________________
3. 
A 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.
What volume of medication should be given to the patient with each dose? _______________________
Which measuring device should be included with the prescription for the patient to take the medication at home? _______________________
What is the measurable dose? _______________________
If the patient should misplace the measuring device provided, how could this be estimated using household utensils? _______________________
4. 
A 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. 
A physician orders penicillin G 450,000 units IM daily for 4 days. The available medication is penicillin G 300,000 units/mL.
What volume of medication should be administered to the patient daily? _______________________
What type of syringe would be needed to administer this strength of medication? _______________________
6. 
A 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.
Interpret the order. __________________________________________________________________
What volume of medication should be administered with each dose? _______________________
Show the correct amount of medication on the correct syringe in the following illustrations.
7. 
A physician orders penicillin G 500,000 units IM q6h. The label reads 1,000,000 units/vial.
If 4 mL of diluent is added to the vial, what is the resultant strength of the penicillin? _______________________
What volume of medication should be prepared for administration? _______________________
How long would this medication be stable after reconstitution? _______________________
Where should the medication be stored after reconstitution? _______________________
What is the total strength of medication in the vial? _______________________
Mark the label with the correct documentation following reconstitution, using today’s date, time, and initials if applicable.
What size syringe should be used for administration of the drug? _______________________
8. 
A 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.
What volume of medication should be administered with each dose? _______________________
If the dose is to be divided between each side of the mouth, what volume of medication should be placed in each side? _______________________
Which measuring device would provide the dosage amount most accurately? _______________________
Indicate the amount of medication on the measuring device to be used.
9. 
A physician orders penicillin V oral suspension 200,000 units po qid. The medication available is penicillin V oral suspension 400,000 units/5 mL.
Interpret the order. _______________________________________________________________
What volume of medication should be administered to the patient? _______________________
How can this be administered using household measuring devices? _______________________
Indicate the amount of medication on the measuring device to be used.
10. 
A 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.
What are the directions for storing this medication? _______________________
What volume of penicillin should be administered to this patient? _______________________
11. 
A physician orders Bicillin L-A 425,000 units IM. The available medication is found on the following label.
What volume of medication should be administered to the patient? _______________________
What is the measurable dose of medication? _______________________
Which syringe should be used to provide the medication? _______________________
Indicate the amount of medication on the proper syringe.
12. 
A physician orders penicillin G potassium 450,000 units IM as a stat dose. The available medication is on the following label.
What is the appropriate concentration of penicillin G potassium on the label for dispensing the medication for this order? _______________________
What volume of diluent should be added to prepare the medication for administration of the desired dose? _______________________
What volume of medication is to be administered following reconstitution? _______________________
What is the proper storage of this medication following reconstitution? _______________________
Show the proper documentation for the reconstitution on the label provided; use today’s date, time, and initials as appropriate.
Which syringe is appropriate for the administration of the medication? _______________________
13. 
A 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.
What volume of medication should be administered? _______________________
Show the volume of diluent to be added on the proper syringe.
Show the volume of medication to be administered on the proper syringe.
Label each syringe with either diluent or medication.
14. 
A 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.
What volume of medication should be administered? _______________________
What is the measurable dose? _______________________
Show the volume of medication on the correct syringe for administration.
15. 
A 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.
What is the total dosage of medication to be given in a day? _______________________
What is the measurable dose in a 3 mL syringe? _______________________
What volume of medication is to be given to the patient to provide each ordered dose? _______________________
16. 
A 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.
What volume of medication should be administered? _______________________
If the medication must be measured from a vial, what syringe should be provided to accurately measure the medication for administration? _______________________
17. 
A 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.
What total dose of medication should be given in a day? _______________________
What dose of medication should be administered with each dose? _______________________
What volume of medication should be administered per dose if the label reads penicillin G 1,000,000 units/50 mL? _______________________
18. 
A 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. 
A 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. 
Mrs. 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.
What volume of medication should be administered to this patient with each dose? _______________________
What measuring device should be included with the prescription for home administration? _______________________
Mrs. Jones calls and states the measuring device given to her to take the medication was stepped on and broken. How would you tell her to take the medication using a household measuring device? _______________________
Explain why using the household measuring device would not provide an accurate dose of medication. _________________________________________________________________
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). Some 100-unit insulin syringes are available in two-unit increments, while others are marked in one-unit increments with two-unit increments of odd/even on each side of the syringe barrel. To further complicate matters when preparing insulin for administration, you will find some syringes are in one-unit increments with the markings on the same side of the syringe. Please note that syringes holding a smaller quantity such as 30-unit and 50-unit syringes are in one-unit increments and are easier to use by patients who have visual problems, a common complication of long-term or uncontrolled diabetes mellitus. Insulin syringes should not be used for measuring any medication other than insulin—not even for heparin or antibiotics.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
