Medical Dosage Calculations A Dimensional Analysis Approach Eleventh Edition Chapter 9 Parenteral Medications

Learning Objectives 9.1 Calculate doses for parenteral medications in liquid form. 9.2 Interpret the directions on drug labels and package inserts for reconstituting medications supplied in powdered form. 9.3 Label reconstituted multidose medication containers with the necessary information. 9.4 Choose the most appropriate diluent volume when reconstituting a multiple-strength medication. 9.5 Calculate doses of parenteral medications measured in units. Slide 2 is list of textbook LO numbers and statements

Figure 9.1 Ampules. Glass container that holds single dose of medication Neck snaps open Use filter needle to withdraw contents

Figure 9.2 Vials. Glass or plastic with rubber membrane on top For medicine in liquid or powdered form Multi-dose or Single-dose (SDV)

Calculations We will be calculating the volume of the solution that contains the prescribed amount of medication ORDER x STRENGTH Check that our result is reasonable compared to the stated strength

Parenteral Medications Supplied as Liquids Example 9.1 (1 of 2) The prescriber ordered 3 milligrams of Dolophine (methadone hydochloride) subcut stat. The strength is 10 mg per mL. How many milliliters would you administer to the patient? 3 mg = ? mL

Parenteral Medications Supplied as Liquids Example 9.1 (2 of 2) The label reads 10 milligrams per milliliter. This strength will be used as the unit fraction:

Parenteral Medications Supplied as Liquids Example 9.2 (1 of 2) The prescriber ordered 0.002 gram of a drug IM stat. The strength is 1 mg per mL. Calculate the number of milliliters of this solution you would administer. You want to convert 0.002 grams to its equivalent in milligrams, and then change milligrams to milliliters

Parenteral Medications Supplied as Liquids Example 9.2 (2 of 2) Because the strength is 1 mg = 1 mL, no further calculations are needed to determine that 2 mg = 2 mL You would administer 2 milliliters of the solution IM, which would contain 0.002 gram of the prescribed drug.

Parenteral Medications Supplied as Liquids Example 9.3 (1 of 3) Determine the quantity of solution to be withdrawn from the vial if the medication order reads 250 milligrams of 10% calcium chloride. 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ= 𝑆𝑜𝑙𝑢𝑡𝑒 𝑆𝑜𝑙𝑢𝑡𝑖𝑜𝑛 10 𝑔 100 𝑚𝐿 = 250 𝑚𝑔 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛

Parenteral Medications Supplied as Liquids Example 9.3 (2 of 3) You want to convert 250 milligrams to milliliters.

Parenteral Medications Supplied as Liquids Example 9.3 (3 of 3)

Parenteral Medications Supplied as Liquids Example 9.4 (1 of 3) The prescriber ordered: heparin 5,000 units subcut q12h. The label on the vial reads 10,000 units per milliliter. How many milliliters will you administer to the patient?

Figure 9.19 Vial of heparin. (For educational purposes only)

Parenteral Medications Supplied as Liquids Example 9.4 (2 of 3) You want to convert 5000 units to milliliters. 5,000 units = ? mL The label on the vial reads 10,000 units per milliliter, so the strength is:

Parenteral Medications Supplied as Liquids Example 9.4 (3 of 3) So, 0.5 milliliter contains 5,000 units of heparin and you would administer 0.5 milliliter of the solution to the patient subcutaneously.

Parenteral Medications Supplied in Powdered Form Powdered Parenteral Medication Some parenteral medications are supplied in powdered form in sealed vials. The powder cannot be removed from these vials. You must add sterile water or saline (diluent) to the vial and dissolve the powder to form a solution. This process is called Reconstitution. You then withdraw from the vial the liquid volume of prepared solution that contains the proper amount of the drug. If there are no directions on the vial for reconstitution, consult a pharmacist or find info from the manufacturer.

Parenteral Medications Supplied in Powdered Form Most common diluents: Sterile water for injection (SW) and 0.9% NaCl (NS – “normal saline”). Displacement Factor is the increase in volume that can occur when you dissolve the drug in a diluent

Figure 9. 45 Drug label for Pfizerpen. (Reg. Trademark of Pfizer Inc Figure 9.45 Drug label for Pfizerpen. (Reg. Trademark of Pfizer Inc. Reproduced with permission.)

Parenteral Medications Supplied in Powdered Form Example 9.5 (1 of 2) The prescriber ordered 150 mg of a drug IM stat. The directions on the 500 mg vial read, “Add 9.7 mL NS and the strength will be 100 mg/mL.” How many milliliters of the reconstituted solution will you administer? ORDER x RECONSTITUTED STRENGTH

Parenteral Medications Supplied in Powdered Form Example 9.5 (2 of 2) You want to convert 150 mg to mL. Using the strength of 100 mg/mL.

Figure 9.10 Reconstitution of ceftriaxone. The prescriber ordered 250 mg.

Chapter Summary (1 of 3) Medications supplied in powdered form must be reconstituted following the manufacturer’s directions. You must determine the best dosage strength when there are several options for reconstituting the medication. After reconstituting a multiple-dose vial, label the medication vial with the dates and times of both preparation and expiration, storage directions, your initials, and strength.

Chapter Summary (2 of 3) When directions on the label are provided for both IM and IV reconstitution, be sure to read the order and the label carefully to determine the necessary amount of diluent to use. Heparin is measured in USP units.

Chapter Summary (3 of 3) It is especially important that heparin orders be carefully checked with the available dosage strength before calculating the amount to be administered. A tuberculin (1 mL) or a 0.5 mL syringe should be used when administering heparin. Heparin sodium and heparin flush solutions are different and should never be used interchangeably.