Injectable Medication Calculations

Introduction

Medications may be ordered to be given by a parenteral route—a route outside of the gastrointestinal tract. This chapter covers injectable medications that may be ordered for the intradermal, subcutaneous, or intramuscular route. Related safety issues are discussed. The dose calculations for mL using the ratio and proportion method have already been covered in Chapter 4 and will be used also in this chapter.

Measuring and Reading Amounts in a Syringe

The best way to learn to read the measurements on a syringe is to examine some unfilled syringes while you read this (Figure 5-1). Then examine some filled syringes, and verify the amounts with your instructor or lab partner.

FIGURE 5-1 Comparison of syringe sizes and calibrations. Note the red arrows where the dose is measured. There are two black rings on the plunger and a rounded or pointed tip. Ignore the rounded/pointed tip and read the uppermost ring, as shown in A. The rings are not shown in C and E so the dose and calibrations can be better visualized. E, 1 mL tuberculin syringe. F, Prefilled syringe with calibration markings. (D, From Becton, Dickinson, and Company, Franklin Lakes, NJ. F, From Macklin D, Chernecky C, Infortuna H: Math for clinical practice, ed 2, St Louis, 2011, Mosby.)

Steps for Measuring and Reading Amounts in a Syringe

1. Examine the total amount the syringe contains first. The 3 mL hypodermic syringe is most commonly used for intramuscular injections and also for subcutaneous injections. The 1 mL tuberculin syringe is used mainly for skin tests.

2. Locate the 1 mL markings on each syringe.

3. Examine the calibrations in 1 mL, 0.2 mL, 0.1 mL, or 0.01 mL, depending on the size of the syringe. The larger the syringe, the larger the calibration.

WORKSHEET 5A

Answers on page 366

Reading Syringe Measurements

Examine the following syringes. Note the total capacity and the 1 mL markings. Indicate the filled-in dose measurements in the space provided.

1. Total capacity: _________ mL
Indicated dose: _________
Smallest measurable dose:_________ mL

2. Total capacity: _________ mL
Indicated dose: _________
Smallest measurable dose:_________ mL

3. Total capacity: _________ mL
Indicated dose: _________
Smallest measurable dose:_________ mL

4. Total capacity: _________ mL
Indicated dose: _________
Smallest measurable dose:_________ mL

5. Total capacity: _________ mL
Indicated dose: _________
Smallest measurable dose:_________ mL

WORKSHEET 5B

Answers on page 367

Syringe Volume Practice

Examine the following syringes. Note the total capacity and the 1 mL and 0.5 mL markings. Fill in the blanks and shade the syringe to the volume requested. If possible, practice with real syringes.

1. Total capacity: _________ mL. Calibrated in tenths or hundredths of a milliliter? (Circle one) Indicate 1.6 mL.

2. Total capacity: _________ mL. Calibrated in 0.1, 0.2, or 0.01 mL increments? (Circle one) Indicate 4.6 mL.

3. Total capacity: _________ mL. Calibrated in 0.1, 0.2, or 0.01 mL increments? (Circle one) Indicate 3.4 mL.

4. Total capacity: _________ mL. Calibrated in tenths or hundredths of a milliliter? (Circle one) Indicate 2.5 mL.

5. Total capacity: _________ mL. Calibrated in tenths or hundredths of a milliliter? (Circle one) Indicate 0.75 mL.

Parenteral Routes

Injectable medications routes known as parenteral (outside the gastrointestinal [GI] tract) include the routes mentioned below as well as intravenous route, which is taught in a later chapter. All equipment and sites are based upon patient size and condition, the type of medication, and the route. Refer to clinical skills manuals for injection techniques.