Reconstitution and Dosages Measured in Units

LEARNING OBJECTIVES

On completion of the materials provided in this chapter, you will be able to perform computations accurately by mastering the following mathematical concepts:

1 Calculating drug dosage problems that first require reconstitution of a powdered drug into a liquid form

2 Using a proportion to solve problems involving drugs measured in unit dosages

3 Drawing a line through an insulin syringe to indicate the number of units desired

A unit is the amount of a drug needed to produce a given result. Various drugs are measured in units; the examples used in this chapter are among the more common drugs prescribed.

Drugs used in this chapter include:

Epogen—A drug that increases the production of red blood cells

Fragmin—An anticoagulant that prevents the clotting of blood

Penicillin—An antibiotic that reduces organisms within the body that cause infection

Heparin—An anticoagulant that inhibits clotting of the blood

Insulin—A hormone secreted by the pancreas that lowers blood glucose

Epogen is a drug that helps to combat the effects of anemia caused by chemotherapy or chronic renal failure. After administering the medicine, the nurse should monitor the patient’s blood pressure and laboratory results on a routine basis.

Fragmin is used in the prevention of deep vein thrombosis after abdominal surgery, hip replacements, and unstable angina/non–Q wave myocardial infarction. It may also be used with patients who have restricted mobility during an acute illness. Fragmin may only be given by subcutaneous injections—never intramuscularly or intravenously. The patient’s blood studies must be monitored on a routine basis during treatment with Fragmin.

Penicillin can be administered orally or parenterally, but heparin, insulin, and epogen must be given subcutaneously or intravenously.

Before administering penicillin, the nurse must confer with the patient regarding previous allergies to the drug. After administering the drug, the nurse must still observe the patient for signs of an allergic reaction.

Because heparin prolongs the time blood takes to clot, the dosage must be accurate. A larger dose may cause hemorrhage, and an insufficient dose may not have the desired result. After administering the drug, the nurse should observe the patient for signs of hemorrhage.

INSULIN

Insulin is used in the treatment of diabetes mellitus. Accuracy is important in the preparation of insulin. A higher dosage than needed may cause insulin shock. An insufficient amount of insulin may result in diabetic coma. Both conditions are extremely serious, and the nurse must be able to recognize the symptoms of each condition so that immediate treatment can be initiated to stabilize the patient. In many institutions, both insulin and heparin dosages are checked for accuracy by another nurse before the drug is administered to the patient. Figure 15-1 shows examples of different types of insulin.

Insulin Syringes

Insulin syringes were developed specifically for the administration of insulin. They are calibrated in units and are available in 30 units, 50 units, and 100 units (Figure 15-2). A U-100 insulin syringe and U-100 insulin are necessary to ensure an accurate insulin dosage. U-100 insulin means that 100 units of insulin are contained in 1 mL of liquid. U-100 insulin is a universal insulin preparation that all persons requiring insulin can use. Another type of U-100 syringe is the U-100 Lo-Dose syringe, which measures 50 units; however, for accuracy, no more than 40 units should be measured in the U-100 Lo-Dose syringe. Because the doses are minute, the U-100 syringe provides the most accurate measurement of insulin dosages. The 30-unit U-100 syringe is used for insulin doses that equal less than 30 units.

FIGURE 15-2 *Left to right:* 30 units measured on a 100-unit syringe (each calibration is 2 units), a 50-unit syringe (each calibration is 1 unit), and 30-unit syringe (each calibration is 1 unit). (From Macklin D, Chernecky C, Infortuna H: *Math for clinical practice*, ed 2, St Louis, 2011, Mosby.)

IMPORTANT NOTE: Only insulin is measured and given in the syringes that are marked in units.* Heparin, penicillin, and other medication measured in units can be measured and given only in syringes marked in milliliters.

ALERT

Only insulin is measured and given in insulin syringes.

Insulin Pens

Insulin is also available in prefilled insulin pens. The insulin pens require a special needle to be attached. Each insulin pen contains a dial to choose the desired number of units to be administered. For example, if 6 units of Novolog insulin are desired, the dial on the Novolog insulin pen would be turned to the Number 6. See Figure 15-3 for examples of insulin pens.

Powder Reconstitution

A drug in powdered form is necessary when a medication is unstable as a liquid form for a long period. This powdered drug must be reconstituted—dissolved with a sterile diluent—before administration. The diluents commonly used include sterile water, sterile normal saline solution, 5% dextrose solution (D₅W), and bacteriostatic normal saline.

Before reconstituting the medication, the nurse must follow several principles:

1. Carefully read the information and directions on the vial or package insert for reconstitution of the medication.

2. If no directions are available with the medication, consult the Physicians’ Desk Reference, hospital drug formulary, pharmacology text, or hospital pharmacy.

3. Identify the type and amount of diluent and the route of administration.

4. Note the drug strength or concentration after reconstitution and circle or place this on the label, if not already written, when you use a multidose vial.

5. Note the length of time for which the medication is good once reconstituted and the directions for storage.

6. Be aware that the total reconstitution amount may be greater than the amount of diluent.

7. After reconstitution of a multidose vial, place your initials, date of preparation, time of preparation, date of expiration, and time of expiration on the label.

EXAMPLE:

a.	What is the route of administration?	IV
b.	What type of diluent can be used?	Check insert
c.	How much diluent must be added?	75 mL, 33 mL, or 11.3 mL
d.	If 75 mL of diluent is added, what is the medication concentration?	250,000 units/mL
e.	How long will the medication maintain its potency at room temperature?	7 days
f.	The physician orders 2,000,000 units IV q4 h. How many milliliters will you give?	8 mL
	Shade the syringe.