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. 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.

What number of tablets should be administered per dose? _______________________

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.

How many suppositories should be used by the patient each night? _______________________

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.

What volume of medication should be provided with each dose? _______________________

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

Buy Membership for Basic Science Category to continue reading. Learn more here