Reconstitution of Solutions

Reconstitution of Solutions

After reviewing this chapter, you should be able to:

1. Prepare a solution from a powdered medication according to directions on the vial or other resources

2. Identify essential information to be placed on the vial of a medication after it is reconstituted

3. Determine the best concentration strength for medications ordered when there are several directions for mixing

4. Identify the varying directions for reconstitution and select the correct directions to prepare the dosage ordered

5. Calculate dosages from reconstituted medications

6. Determine the rate in milliliters per hour for enteral feedings

7. Calculate the amount of solute and solvent needed to prepare a desired strength for enteral feedings

Some medications are unstable when stored in liquid form for long periods of time and therefore are packaged in powdered form. When medications come in powdered form, they must be diluted with a liquid referred to as a diluent or solvent before they can be administered to a client. Once a liquid is added to a powdered medication, the solution may be used for only 1 to 14 days, depending on the type of medication. The process of adding a solvent or diluent to a medication in powdered form to dissolve it and form a solution is referred to as reconstitution. Reconstitution is necessary for medications that come in powdered form before they can be measured and administered. If you think about it, this process is something you do in everyday situations. For example, when you make iced tea (powdered form), in essence you are reconstituting it. The iced tea, for example, is the powder, and the water you add to it is considered the diluent, or solvent.

As a safety precaution in some institutions, the pharmacy reconstitutes most medications. However, the nurse must understand the process of reconstitution because some medications may have to be reconstituted just before administration. Medications requiring reconstitution can be for oral or parenteral use; these are not always injectable medications. With emphasis being placed on home care, nurses and other health care providers may have to dilute things such as oral medications, irrigating solutions, and nutritional feedings. Sterile solutions are always used to reconstitute medications for injectable use. Special diluents, when required for reconstitution, are usually packaged with the powdered medication; but oral medications can often be, but are not always, reconstituted with tap water. Thus the nurse must know how the reconstitution process works. Understanding the terminology relating to reconstitution enables the nurse to understand the process:

• Solute—a powdered medication or liquid concentrate to be dissolved or diluted.

• Solvent (diluent)—a liquid that is added to the powder or liquid concentrate. The nurse must identify the solvent (diluent) to use. The type of solvent (diluent) varies according to the medication. The package insert or the medication label will indicate the solvent (diluent) to be used and the amount. If the information is not indicated on the label or the package insert is unavailable consult the pharmacy or a medication reference such as the Physician’s Desk Reference (PDR), a medication reference, or the hospital formulary.

• Solution—the liquid that results when the solvent (diluent) dissolves the solute (powdered medication or liquid concentrate).

BASIC PRINCIPLES FOR RECONSTITUTION

The first step in reconstitution is to find the directions and carefully read the information on the vial or the package insert. Medications labeled and packaged with reconstitution directions may indicate “oral, IM, or IV use only” or may say “can be used for any route.” Carefully check the route of administration of the medication and the reconstitution directions. Examples of the several directions for reconstitution are shown in this chapter.

Before reconstituting a medication, read and follow the directions on the label or package insert. This includes checking the expiration date on the medication and diluent. Never assume the type or amount of diluent to be used. Consult the appropriate resources if the information is not available.

1. The drug manufacturer provides directions for reconstitution, including information regarding the number of milliliters of diluent or solvent that should be added, as well as the type of solution that should be used to reconstitute the medication. The concentration (or strength) of the medication after it has been reconstituted according to the directions is also indicated on some medications. The directions for reconstitution must be read carefully and followed.

2. The diluent (solvent, liquid) commonly used for reconstitution is sterile water or sterile normal saline solution, prepared for injection. Other solutions that may be used are 5% dextrose and water and bacteriostatic water. Some powdered medications for oral use may be reconstituted with tap water. The manufacturer’s directions will tell you which solution to use. If the medication requires a special solution for reconstitution, it is usually supplied by the drug manufacturer and packaged with the medication (e.g., Librium).

3. Once you have located the reconstitution directions on the label, you need to identify the following information:

a. The type of diluent to use for reconstitution.

b. The amount of diluent to add. This is essential because directions relating to the amount can vary according to the route of administration. There may be different dilution instructions for intravenous (IV) versus intramuscular (IM) administration.

c. The length of time the medication is good once it is reconstituted. The length of time a medication can be stored once reconstituted can vary depending on how it is stored. When medications are reconstituted the solution must be used in a timely fashion. The potency (stability) of the medication may be several hours to several days or a week. Check the medication label, package insert, or appropriate resources for how long a medication may be used after reconstitution.

d. Directions for storing the medication after mixing. Medications must be stored appropriately once reconstituted per manufacturer’s instructions to ensure optimal potency of the medication. Medications can become unstable when stored incorrectly and for long periods. Example: A label may state a medication maintains its potency 96 hours at room temperature or 7 days when refrigerated.

e. The strength or concentration of the medication after it has been reconstituted.

Refer to Figure 19-1 showing the oxacillin sodium reconstitution procedure. Note that directions on the label say to add 2.7 mL sterile water for injection and that each 1.5 mL contains 250 mg. The available dosage after reconstitution is 250 mg of oxacillin per 1.5 mL solution (500 mg per 3 mL).

Figure 19-1 Oxacillin reconstitution procedure. (Modified from Brown M, Mulholland JL: Drug calculations: process and problems for clinical practice, ed. 8, St. Louis, 2008, Mosby.)

4. If there are no directions for reconstitution on the label or on a package insert, or if any of the information (listed in number 3) is missing, consult appropriate resources such as the Physician’s Desk Reference (PDR), a pharmacology text, the hospital drug formulary or the pharmacy.

5. Injectable medications for reconstitution can come in a single-dose vial or a multiple-dose vial. When medications are in single-dose vials, there is only enough medication for one dose and the contents are administered after reconstitution. In the case where the nurse reconstitutes a multiple-dose vial, there is enough medication for more than one dose. Therefore, when a multiple-dose vial is reconstituted, it is important to clearly label the vial after reconstitution with the following information:

a. The date and time prepared, dosage strength prepared, the expiration date for the medication once reconstituted, and the time. Note: If all of the solution that is mixed is used, this information is not necessary. Information regarding the date and time of preparation and date and time of expiration is crucial when all of the medication is not used.

b. Storage directions such as “Refrigerate.”

c. Your initials.

If the medication label does not have room to clearly write the required information, add a label to the vial and indicate important information. Make certain the label is applied so that it does not obscure the medication name and dosage.

Tips for Clinical Practice

When reconstituting a multiple-dose medication vial, label it with the required information and store it appropriately. If the vial is not labeled with a date and time, the medication must be discarded.

6. When reconstituting medications that are in multiple-dose vials or have several directions for preparation, information regarding the dosage strength or final concentration (what the medication’s strength or concentration is after you mixed it) must be on the label; for example, 500 mg per mL. This is important because others using the medication after you need this information to determine the dosage.

7. After the diluent is added to a powder, some medications completely dissolve and there is no additional volume added. Often, however, the powdered medication adds volume to the solution. The powdered medication takes up space as it dissolves and results in an increase in the amount of total (fluid) volume once it has dissolved. This is sometimes referred to as the displacement factor, or just displacement. The reconstituted material represents the diluent and powder. For example, directions for 1 g of powdered medication may state to add 2.5 mL sterile water for injection to provide an approximate volume of 3 mL (330 mg per mL). When the 2.5 mL of diluent is added, the 1 g of powdered medication displaces an additional 0.5 mL, for a total volume of 3 mL. The available dosage after reconstitution is 330 mg per milliliter of solution.

Always determine both the type and amount of diluent to be used for reconstituting medications. Read and follow the label or package insert directions carefully to ensure that your client receives the intended dosage. Consult a pharmacist or other appropriate resources if there are any questions. Never assume!

Tips for Clinical Practice

If the powder displaces the liquid as it dissolves and increases the volume as illustrated in the example, the resulting volume and concentration must be considered when the correct dosage of medication is calculated. Whether a medication causes an increase in volume when it is reconstituted will be indicated on the medication label or the package insert.

The two types of reconstituted parenteral solutions are single strength and multiple strength. A single-strength solution has the directions for reconstitution printed on the label, as shown on the 500-mg oxacillin label in Figure 19-1. A multiple-strength solution usually has several directions for reconstitution and requires the nurse be even more attentive to the directions to select the best concentration to administer the required dosage.

Always consult the label, package insert, or other sources regarding directions for reconstituting medications in powdered form to ensure accurate reconstitution for administration.

Let’s do some practice problems answering questions relating to single-strength solutions.

Practice Problems

Using the label for ampicillin, answer the following questions.

1. What is the total dosage strength of ampicillin in this vial? _________________________________

2. How much diluent is added to the vial to prepare the medication for IM use? _________________________________

3. What diluent is recommended for reconstitution? _________________________________

4. What is the final concentration of the prepared solution for IM administration? _________________________________

5. How long will the reconstituted material retain its potency? _________________________________

6. 500 mg IM q6h is ordered. How many milliliters will you give? Shade the dosage in on the syringe provided. _________________________________

Using the label for Tazidime, answer the following questions.

7. What is the total dosage strength of Tazidime in the vial? ___________________________________

8. How much diluent is added to the vial to prepare the medication for IM use? ___________________________________

9. What diluent is recommended for reconstitution for IM administration? ___________________________________

10. What is the final concentration of the solution prepared for IM administration? ___________________________________

11. How long does the medication retain its potency at room temperature? _________________________________

12. How long does the medication retain its potency if it is refrigerated? ___________________________________

13. 400 mg IM q8h is ordered. How many milliliters will you give? Shade the dosage in on the syringe provided. ___________________________________

Using the label for Ticar, answer the following questions.

14. What is the total dosage strength of Ticar in the vial? ___________________________________

15. What diluent is recommended to prepare an IV dosage? ___________________________________

16. How many milliliters of diluent are needed to prepare an IM dosage? ___________________________________

17. What is the final concentration of the solution prepared for IM administration? ___________________________________

18. Ticar 500 mg IM q8h is ordered. How many milliliters will you give? Shade the dosage in on the syringe provided. ___________________________________

Using the label for Rocephin, answer the following questions.

19. What is the total dosage strength of Rocephin in this vial? ___________________________________

20. For what routes of administration is the medication indicated? ___________________________________

21. How much diluent must be added to the vial to prepare the medication for IV use?_______________________________

22. What kind of diluent is recommended for IV reconstitution? ___________________________________

23. What is the final concentration of the prepared solution for IV use? ___________________________________

24. How much diluent must be added to the vial to prepare the medication for IM use? _________________________________

25. What kind of diluent is recommended for IM reconstitution? ___________________________________

26. 1 g IV q12h is ordered. How many milliliters will you give? Shade the dosage in on the syringe provided. __________________________________

Using the label for Augmentin, answer the following questions.

27. How much diluent must be added to prepare the solution? ___________________________________

28. What type of solution is used for the diluent? ___________________________________

29. What is the final concentration of the prepared solution? ___________________________________

30. How should the medication be stored after it is reconstituted? ___________________________________

Using the label for Zovirax and a portion of the package insert, answer the following questions.

31. What is the total dosage strength of Zovirax in this vial? ___________________________________

32. How much diluent must be added to prepare the solution? ___________________________________

33. What diluent is recommended for reconstitution? ___________________________________

34. What is the final concentration of the prepared solution? ___________________________________

35. What is the route of administration? ________________________

Using the label for erythromycin, answer the following questions.

36. How much diluent must be added to prepare the solution? ___________________________________

37. What is the volume of the solution after it is mixed? ___________________________________

38. What is the final concentration of the prepared solution? ___________________________________

39. For how long is the reconstituted solution good? ___________________________________

Using the label for Zithromax, answer the following questions.

40. What is the total dosage strength of Zithromax in this vial? ___________________________________

41. How much diluent must be added to prepare the solution? ___________________________________

42. What diluent is recommended for reconstitution? ___________________________________

43. What is the final concentration of the prepared solution? ___________________________________

44. What is the route of administration? ________________________

Using the label for cefazolin, answer the following questions.

45. What is the total dosage strength of cefazolin in this vial? ___________________________________

46. How many milliliters of diluent are needed to prepare an IM dosage? ___________________________________

47. What diluent is recommended for reconstitution? ___________________________________

48. What is the final concentration of the prepared solution? ___________________________________

49. How long does the medication maintain its potency at room temperature? ___________________________________

Using the label for fluconazole, answer the following questions.

50. How much diluent must be added to prepare the solution? ___________________________________

51. What diluent is recommended for reconstitution? ___________________________________

52. What is the final concentration of the prepared solution? ___________________________________

53. How should the medication be stored after it is reconstituted? ___________________________________

Answers on pp. 642–643

Calculation of Medications When the Final Concentration (Dosage Strength) Is Not Stated

Sometimes a medication comes with directions for only one way to reconstitute it, and the label does not indicate the final dosage strength after it is mixed, such as “becomes 250 mg per mL.” Example: A particular medication is available in 1 g in powder. Directions tell you that adding 2.5 mL of sterile water yields 3 mL of solution. When you add 2.5 mL of sterile water to the powder, the volume expands to 3 mL. The concentration is not changing; you will get 3 mL of solution; however, it will be equal to 1 g.

The problem is therefore calculated by using 1 g = 3 mL.

RECONSTITUTING MEDICATIONS WITH MORE THAN ONE DIRECTION FOR MIXING (MULTIPLE STRENGTH)

Remember the directions for reconstitution can be on the label or a package insert. At times the vial will contain minimal information. It may only include the dosage strength and state “see package insert for directions for reconstitution or storage.”

Some medications in addition to giving the route of administration may come with several directions for preparing different solution strengths. In this case the nurse must choose the concentration or dosage strength appropriate for the dosage ordered. A common medication that has a choice of dosage strengths is penicillin. When a medication comes with several directions for preparation or offers a choice of dosage strengths, you must choose the strength most appropriate for the dosage ordered. The following guidelines may be used.

Guidelines for Choosing Appropriate Concentrations

1. Consider the route of administration.

a. IM—You are concerned that the amount does not exceed the maximum allowed for IM administration. However, you do not want to choose a concentration that will result in irritation when injected into a muscle. When a choice of strengths can be made, do not choose an amount that would exceed the amount allowed for IM administration or one that is very concentrated.

b. IV—Keep in mind that this medication is usually further diluted because once reconstituted, the medication is then placed in additional fluid of 50 to 100 mL or more, depending on the medication being administered. Example: Erythromycin requires that the reconstituted solution be placed in 250 mL of fluid before administration to a client. In pediatrics a medication may be given in a smaller volume of fluid, depending on the child’s age, the child’s size, and the medication.

2. Choose the concentration or dosage strength that comes closest to what the prescriber has ordered. The dosage strengths are given for the amount of diluent used. Example: If the prescriber orders 300,000 units of a particular medication IM, and the choices of strength are 200,000 units per mL, 250,000 units per mL, and 500,000 units per mL, the strength closest to 300,000 units per mL is 250,000 units per mL. It allows you to administer a dosage within the range allowed for IM administration, and it is not the most concentrated.

When multiple directions are given for reconstituting medications, the smaller the amount of diluent used to reconstitute the medication, the more concentrated the resulting solution will be. Consider the route of administration when reconstituting medications. Always check the route and the directions related to reconstitution.

3. The word respectively may sometimes be used on a medication label for directions on reconstitution. For example, reconstitute with 23 mL, 18 mL, 8 mL of diluent to provide concentrations of 200,000 units per mL, 250,000 units per mL, 500,000 units per mL, respectively. The word respectively means in the order given. In terms of the directions for reconstitution, this means that if you add 23 mL diluent, it will provide 200,000 units per mL, 18 mL diluent will provide 250,000 units per mL, etc. In other words, the amounts of diluent correspond to the order in which the concentrations are written. Remember: When you are mixing a medication that is a multiple-strength solution, the dosage strength that you prepare must be written on the vial.

Let’s look at a sample label that shows a multiple-strength solution.

Notice that the penicillin label states one million units. This means a total of 1,000,000 units of penicillin is in the vial. The directions for reconstitution and the dosage strengths that can be obtained are listed on the right side of the label. If the dosage ordered for the client was, for example, 250,000 units q6h, the most appropriate strength to mix would be 250,000 units per mL. If you look next to the dosage strength in the directions, you will notice that 4 mL of diluent must be added to obtain a concentration of 250,000 units per mL. Because this is a multiple-strength solution, the dosage strength you choose must be indicated on the vial after you reconstitute it. Since the type of diluent is not indicated on the label, other resources, such as those recommended previously, must be consulted.

If a multiple-strength solution is prepared and not used in its entirety, the dosage strength (final concentration) you mixed must be indicated on the label to verify the dosage strength of the reconstituted solution. Proper labeling is a crucial detail.

Practice Problems

Using the label for penicillin G potassium, answer the following questions.

54. What is the total number of units of penicillin contained in the vial? (Write out in numbers.) ___________________________________

55. If you add 33 mL of diluent to the vial, what dosage strength will you print on the label? ___________________________________

56. If 2,000,000 units IV is ordered, which dosage strength would be appropriate to use? ___________________________________

57. How many milliliters will you administer? _________________________________

58. How long will the medication maintain its potency if refrigerated? ___________________________________

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Feb 11, 2017 | Posted by admin in PHARMACY | Comments Off

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