mckennon pharm ch06

is administered into a blood vessel (typically through a vein). Unlike an injection, an infusion is used for both small and large volumes of fluid. Medications given as injec-tions or infusions are considered parenteral, which literally means “occurring outside the intestines.” In other words, the medications do not pass through the gastrointesti-nal system.

Injecting MedicationsThere are three main types of injections: subcutaneous injections, intramuscular injections, and intravenous infusions. All three types of injections are administered by healthcare professionals on a regular basis.

A subcutaneous (subcut, SC, or SQ) injection is administered into the vascu-lar, fatty layer of tissue under the layers of skin. Most medications given by this route of administration are quickly absorbed. Patients can self-administer medications such as insulin by subcut injection.

An intramuscular (IM) injection is administered into the muscle tissue. Water-soluble medications are absorbed rapidly when given intramuscularly, whereas oil-based medications are absorbed slowly. With proper training, patients can self-administer medications by IM injection, but this route requires more skill and coordi-nation than the subcut route of administration.

An intravenous (IV) infusion is administered into a vein. Large-volume IV infu-sions, such as 500–1,000 mL, may be administered over a period of hours. IV infusions of 50–100 mL are often given over a period of 30–60 minutes. A smaller volume, such as 5–30 mL, may be given via a syringe as an IV push medication over a few minutes. Most IV infusions are administered to inpatients, although these infusions can also be given in a clinic or at home with proper training of home healthcare personnel.

Measuring Injection ComponentsBecause injectable medications are adminis-tered directly into the body, these medications must be specially compounded in a controlled environment that is as sterile, or germ-free, as possible. The preparation of injectable medica-tions requires special training and the use of specific supply items. Most medications are combined with base solutions prior to injec-tion. A base solution is a sterile solution com-patible with human blood that serves as a vehi-cle for the delivery of medications. Commonly used base solutions include sterile water for injection (SWFI) as well as manufactured mix-tures of dextrose in water (often dextrose 5% in water [D

5W]) or sodium chloride solutions (often sodium chloride [NaCl] 0.9% or 0.45% solutions).

Put Down Roots

The word intra-muscular comes from two Latin roots: intra, mean-ing “inward,” and musculus, mean-ing “little mouse” because the shape and movement of the biceps resemble a mouse. Therefore, an intramuscular injection is given “within the muscle.”

Put Down Roots

The word subcuta-neous comes from two Latin roots: sub, meaning “under,” and cutis, meaning “skin.” Therefore, a subcutaneous injection is given “under the skin.”

Name Exchange

Injectable 0.9% sodium chloride solution is often referred to as normal saline (abbreviated as NS)in healthcare settings.

This image shows a manufactured mixture of 0.9% sodium chloride. This base solution may be administered with or without a medication added.

6.1 Injectable Dose Calculations Injection is the act of administering a medication or other substance into the body. In injections, a needle or cannula (a small tube) attached to a syringe pen-etrates the skin or a membrane to deposit medication into the tissue, muscle, or vessel below. An infusion is a type of injection in which a large volume of fluid

Pharmacy Technician Series © Paradigm Education SolutionsPharmacy Calculations for Technicians, Seventh Edition: Chapter 6, Section 6.1

Volumes of medications and, at times, base solutions must be measured. Syringes are typically used for the volumetric measurement of injectable products. A syringe is a device that contains a hollow barrel (with calibration marks) and a pis-ton plunger to withdraw or inject liquid. Syringes are available in a variety of sizes. Typical syringe sizes include 1 mL, 3 mL, 5 mL, 10 mL, 20 mL, or 50 mL. Smaller syringes are marked to indicate volume using fifths, tenths, or other fractions of a milliliter. Larger syringes are marked in 1 mL or 2 mL increments. For accuracy, it is best to select the smallest syringe that will hold the desired volume.

Calculating the Volume of an Injectable SolutionMedications given by injection are often ordered in milligrams, and the pharmacy or nursing staff must select and prepare an appropriate concentration of medication from the available stock medication. The volume of medication to be used (either directly administered to a patient or added to a base solution) must be calculated.

The following examples demonstrate how to calculate the volume of medication using the ratio-proportion and dimensional analysis methods. A small volume (less than 20 mL) is rounded to the nearest tenth or hundredth of a milliliter, depending on the size of the syringe barrel and its degree of accuracy. Larger volumes are rounded to the nearest tenth or whole milliliter.

Ideally, you should choose a syringe that provides the most accurate volume measurement. Typically, the smaller the syringe, the more accurate its mea-

surement. The total volume to be prepared should generally fill at least half of the syringe barrel. For example, when measuring 2.8 mL of medication, the selection of a 3 mL or 5 mL syringe would be appropriate because the 2.8 mL would fill half or more of either syringe. If you chose the 10 mL syringe for dispensing 2.8 mL, the volume of fluid might not be measured as accurately as it would be in the smaller syringes.

WORKPLACE WISDOM

SafetyAlert

Because all syringes are not marked using the same incre-ments, pharmacy technicians should become familiar with the demarca-tions (calibrations) of syringe sizes before using these measuring devices.

Syringes range in both volume and marked increments.

Example 6.1.1

How many milliliters of the medication shown in the label below must be prepared to provide 12.5 mg to a patient?

You can solve this problem by using the ratio-proportion method or by using the dimensional analysis method.

Ratio-Proportion Method

To begin, set up a proportion with the desired medication amount on one side and the available drug concentration on the other side. Remember that the units of measurement in the numerators and in the denominators must match. Then, cross multiply, cancel similar units (like terms), and divide to solve for the unknown variable x.

12.5 mg_______

x mL =

5 mg_____1 mL

x mL (5 mg) = 1 mL (12.5 mg)

x = 2.5 mL

Dimensional Analysis Method

12.5 mg_______ 1

3 1 mL_____5 mg

= 2.5 mL

Answer: To provide 12.5 mg of midazolam to the patient, you must prepare 2.5 mL in a 3 mL syringe (see Figure 6.1).

Example 6.1.2

How many milliliters of the medication shown in the label below must be prepared to provide 8 mg of ondansetron to a patient?


Name Exchange

The generic medica-tion midazolam is commonly known as the brand name Versed.

1 mL Vial

NDC 0000-0000-000

Midazolam HCl

5 mg/1 mL

Rx Only

For Intravenous or Intramuscular Use

Injection

Name Exchange

The generic medica-tion ondansetron is commonly known by the brand name Zofran.

2 mL Single-Dose Vial

NDC 0000-0000-000

Ondansetron

4 mg/2 mL

Rx Only

For Intramuscular or Intravenous Use

Injection

(2 mg/mL)

0.5

1

1.5

2

2.5

3mL

FIGURE 6.1

2.5 mL of medication in a 3 mL syringe



8 mg_____x mL =

4 mg_____2 mL

x mL (4 mg) = 2 mL (8 mg)

x = 4 mL


8 mg_____1 3

2 mL______4 mg = 4 mL

Answer: To provide 8 mg of ondansetron to the patient, you must prepare 4 mL in a 5 mL syringe (see Figure 6.2).

Example 6.1.3

How many milliliters of medication shown in the label below must be prepared to provide 10 mg of adenosine?




10 mg______x mL =

12 mg______4 mL

x mL (12 mg) = 4 mL (10 mg)

x = 3.3 mL


NDC 0000-0000-000

Adenosine

12 mg/4 mL

Rx Only

For Rapid Bolus Intravenous Use

Injection

(3 mg/mL)

1

2

3

4

5mL

FIGURE 6.2

4 mL of medication in a 5 mL syringe

1

2

3

4

5mL

.5 mL

1.5 mL

2.5 mL

3.5 mL

4.5 mL

3.3 mL

FIGURE 6.3

3.3 mL of medication in a 5 mL syringe


10 mg _____

1 3

4 mL ______

12 mg = 3.3 mL

Answer: To provide 10 mg of adenosine to the patient, you must prepare 3.3 mL in a 5 mL syringe (see Figure 6.3).

Calculating the Quantity of Medication in an Injectable SolutionThe previous examples demonstrated how to calculate the volume of an injectable solu-tion needed to obtain a desired quantity of medication. As a pharmacy technician, you will also have situations in which you need to perform the opposite calculation. You will need to determine the quantity of medication in a given volume of an injectable solution.

Example 6.1.4

How many milligrams of progesterone are in 2 mL of the solution shown in the label below?



To begin, set up a proportion with the desired medication volume on one side and the available drug concentration on the other side. Remember that the units of measurement in the numerators and in the denominators must match. Then, cross multiply, cancel similar units (like terms), and divide to solve for the unknown variable x.

x mg

_____ 2 mL

= 50 mg

______ 1 mL

x mg (1 mL) = 50 mg (2 mL)

x = 100 mg


2 mL _____

1 3

50 mg ______

1 mL 5 100 mg

Answer: There are 100 mg of progesterone in 2 mL of the solution.

10 mL Multiple-Dose Vial

NDC 0000-0000-000

Rx Only

Progesterone

50 mg/mL

For Intramuscular Use Only

Injection

Example 6.1.5

How many milligrams of carboplatin are in 30 mL of the solution shown in the label below?




x mg

______ 30 mL

= 450 mg

_______ 45 mL

x mg (45 mL) = 450 mg (30 mL)

x = 300 mg


30 mL

______ 1 3 450 mg

_______ 45 mL

= 300 mg

Answer: There are 300 mg of carboplatin in 30 mL of the solution.

Example 6.1.6

How many milligrams of furosemide are in 6 mL of the solution shown in the label below?

Multiple-Dose Vial

NDC 0000-0000-000

Carboplatin

450 mg/45 mL

Rx Only

For Intravenous Use

Injection

(10 mg/mL)


NDC 0000-0000-000

Furosemide

Preservative-Free

For Intramuscular or Intravenous Use

20 mg/2 mL

(10 mg/mL)

Injection

Rx Only




x mg

_____ 6 mL

= 20 mg

______ 2 mL

x mg (2 mL) = 20 mg (6 mL)

x = 60 m g


6 mL _____

1 3

20 mg ______

2 mL = 60 mg

Answer: There are 60 mg of furosemide in 6 mL of the solution.

Calculating Ratio StrengthAs you learned in Chapter 2, a ratio can be used to express the strength or concentra-tion of a drug. For example, a 1% solution could be written as 1:100. The ratio 1:100 is referred to as a ratio strength and is an alternate way to indicate medication strength for liquids.

Ratio strength is expressed by the ratio a:b (read as “a to b”). In this ratio, a repre-sents parts of active drug, and b represents parts of a liquid solution. Therefore, ratio strength is defined as the parts of active drug in a liquid solution. The units indicated in a ratio strength are always a grams:b milliliters. Consequently, the ratio 1:100 repre-sents 1 g of active drug in 100 mL of solution.

The following examples utilize methods to determine the quantity of active drug or volume for medications expressed in ratio strength.

Example 6.1.7

How many grams of active drug are in 500 mL of a 1:200 solution?



To begin, set up a proportion with the medication volume on one side and the available drug’s ratio strength on the other side. Remember that the units of measurement in the numerators and in the denominators must match. Then, cross multiply, cancel similar units (like terms), and divide to solve for the unknown variable x.

x g _______

500 mL =

1 g _______

200 mL

x g (200 mL) = 1 g (500 mL)

x = 2.5 g


500 mL

_______ 1

3 1 g _______

200 mL = 2.5 g

Answer: There are 2.5 g of active drug in 500 mL of a 1:200 solution.

Example 6.1.8

How many grams of active drug are in 500 mL of a 1:3,000 solution?



To begin, set up a proportion with the medication volume on one side and the available drug’s ratio strength on the other side. Remember that the units of measurement in the numerators and in the denominators must match. Then, cross multiply, cancel similar units (like terms), and divide to solve for the unknown variable x.

x g _______

500 mL =

1 g _________

3,000 mL

x g (3,000 mL) = 1 g (500 mL)

x = 0.17 g


500 mL

_______ 1

3 1 g _______

3000 mL = 0.17 g

Answer: There is 0.17 g of active drug in 500 mL of a 1:3,000 solution.

Example 6.1.9

How many milligrams of active drug are in 1.5 mL of a 1:1,000 solution of epinephrine?



First, convert the ratio strength from units of grams per milliliter to milligrams per milliliter.

x mg

_____ 1 g

= 1,000 mg

_______ 1 g

x mg (1 g) = 1,000 mg (1 g)

x = 1,000 mg

We now can rewrite the drug’s ratio strength as 1,000 mg/1,000 ml.

Now, set up a proportion with the medication volume on one side and the available drug’s ratio strength on the other side. Remember that the units of measurement in the numerators and in the denominators must match. Then, cross multiply, cancel similar units (like terms), and divide to solve for the unknown variable x.

x mg

______ 1.5 mL

= 1,000 mg

_______ 1,000 mL

x mg (1,000 mL) = 1,000 mg (1.5 mL)

x = 1.5 mg


1.5 mL

______ 1

3 1 g _______

1,000 mL 3

1,000 mg _______

1 g = 1.5 mg

Answer: There are 1.5 mg of active drug in 1.5 mL of a 1:1,000 solution of epinephrine.

Example 6.1.10

How many milligrams of active drug are in 3 mL of a 1:2,500 solution?



To begin, set up your calculation using grams. Create a proportion with the medication volume on one side and the available drug’s ratio strength on the other side. Remember that the units of measurement in the numerators and in the denominators must match. Then, cross multiply, cancel similar units (like terms), and divide to solve for the unknown variable x.

x g

_____ 3 mL

= 1 g _________

2,500 mL

x g (2,500 mL) = 1 g (3 mL)

x = 0.0012 g

Next, use your answer in the first calculation (0.0012 g) and set up a conversion from grams to milligrams.

x mg

________ 0.0012 g

= 1,000 mg

________ 1 g

x mg (1 g) = 1,000 mg (0.0012 g)

x = 1.2 mg

Alternatively, you can use your answer in the first calculation (0.0012 g) and simply move the decimal point three places to the right.

0.0012 g = 1.2 mg


3 mL _____

1 3

1 g _______

2,500 mL 3

1,000 mg _______

1 g = 1.2 mg

Answer: There are 1.2 mg of active drug in 3 mL of a 1:2,500 solution.

Example 6.1.11

How many milliliters are needed to provide 0.75 g of a medication if the solution available is 1:2,000?



To begin, set up a proportion with the medication amount on one side and the available drug’s ratio strength on the other side. Remember that the units of measurement in the numerators and in the denominators must match. Then, cross multiply, cancel similar units (like terms) and divide to solve for the unknown variable x.

0.75 g

______ x mL

= 1 g _________

2,000 mL

x mL (1 g) = 2,000 mL (0.75 g)

x = 1,500 mL


0.75 g

_____ 1

3 2,000 mL

_________ 1 g

5 1,500 mL

Answer: For a 1:2,000 solution, a volume of 1,500 mL is needed to provide 0.75 g of a medication.

Example 6.1.12

How many milliliters are needed to provide 20 mg of a medication if the solution available is 1:500?



To begin, convert the desired dose units from milligrams to grams.

x g _____

20 mg =

1 g _______

1,000 mg

x g (1,000 mg) = 1 g (20 mg)

x = 0.02 g

Next, set up a proportion with the medication amount on one side and the avail-able drug’s ratio strength on the other side. Remember that the units of mea-surement in the numerators and in the denominators must match. Then, cross multiply, cancel similar units (like terms), and divide to solve for the unknown variable x.

0.02 g

______ x mL

= 1 g _______

500 mL

x mL (1 g) = 500 mL (0.02 g)

x = 10 mL


20 mg

_____ 1

3 1 g _______

1,000 mg 3

500 mL _______

1 g = 10 mL

Answer: For a 1:500 solution, a volume of 10 mL is needed to provide 20 mg of a medication.

mckennon pharm ch06

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