Reconstitution of Powders or Crystals into Liquid Medications

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Chapter 9

Reconstitution of Powders or Crystals into Liquid Medications

Pretest

Complete the following reconstitution of the medications to supply the dosage necessary for a physician’s order. Show your calculations. Be sure all calculations are made to a measurable amount.

image 1 A physician orders penicillin G 200,000 units to be given IM q12h × 5 d for a child. As the pharmacy technician in the hospital pharmacy, you are to prepare the powdered medication for administration by injection. It is desirable for the intramuscular (IM) injection dose not to exceed 1 mL in volume for this child. You have the label for a multidose vial from which to prepare the medication. Determine the correct reconstituted concentration for use with this patient.

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image 2 A physician orders penicillin G 250,000 units q6h IM. The medication is available in a 1,000,000-unit multidose vial. The label reads to reconstitute the medication with either sterile water for injection or isotonic sodium chloride for injection using the following instructions:

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image 3 A physician orders Mefoxin 1.2 g IM q8h. The medication available is a 2-g vial for reconstitution. The label reads as follows:

MEFOXIN CONCENTRATION AMOUNT OF DILUENT TO BE ADDED AMOUNT THAT CAN BE DRAWN
400 mg/mL 4 mL for IM use 5 mL
180 mg/mL 10 mL for IV use 10.5 mL

image 4 A physician orders ampicillin 500 mg IM q6h. The available medication is a 1-g vial. The following label is on the vial:

AMPICILLIN CONCENTRATION AMOUNT OF DILUENT
250 mg/mL 3.4 mL

image 5 A bottle of ampicillin is marked 125 mg/5 mL for a child. The 200-mL bottle instructs that 158 mL of water be added for an oral suspension. The physician wants the child to receive ampicillin 250 mg qid.

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What is the total strength of medication in milligrams in the bottle? __________

Hint: Use ratio and proportion to complete this answer.

What volume of water is added for the bottle to have the correct concentration? _________ Show on the graduates the volume of water needed for reconstitution.

What is the volume per dose that the child should receive? ____________________

What dose volume would you tell the parent to give in household measurements? ____________________

Is the volume in the one container sufficient for 10 days? __________ Show your work. Explain your answer. ____________________

If necessary, how many mL of medication are needed to complete the prescription as designated? ____________________

What is the total volume of liquid in milliliters in the container after reconstitution? ____________________

What is the powder volume of this medication? ____________________

image 6 A bottle of Veetids after reconstitution will contain 125 mg/5 mL. The bottle states that the total volume in the bottle will be 100 mL after reconstitution.

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image 7 A label for ticarcillin for injection for IV and IM use shows that the vial contains 1 g of medication in 2.6 mL of reconstituted medication for IM use. The instructions state to use at least 4 mL of sterile water for injection for IV use. To prepare an IM solution, add 2 mL of sterile diluent. Use the solution promptly after reconstitution.

What is the dosage strength found in this vial once prepared for IM use? ____________________

What is the diluent volume for IM use? ____________________

If 5 mL of sterile water has been added to the medication for IV use, what volume of medication would be added to the IV fluids to provide the medication for an order of 750 mg? Base your answer on the fact that the entire vial will contain 6 mL of medication. ____________________

What volume of medication is prepared for injection if the physician orders 500 mg IM stat? ____________________

The physician then orders 250 mg IM every 8 hours. What volume of medication would be given with each dose? ____________________

Can the remainder of the vial be used for the subsequent injections? ____________________ Explain your answer. ____________________

image 8 A vial of Solu-Medrol is being reconstituted for a patient with severe allergies. The label reads to reconstitute the medication with 8 mL of bacteriostatic water for injection with benzyl alcohol. When reconstituted, each 8 mL will contain 500 mg. The solution will remain stable between 15° and 30° C for 48 hours after mixing.

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What is the total strength of medication in a vial? ____________________

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    What is the total strength of medication in the container in grams? __________

What is the diluent volume that should be added to the medication when reconstituting to the strength designated on the container? ____________________

Show on the graduates the water volume to be added to the solid medication.

What is the dose strength of the medication following reconstitution? __________

How long is the medication stable after reconstitution, when stored as indicated? ____________________

What storage information needs to be supplied to the patient when this medication is dispensed? ____________________

What volume of medication is necessary to give a child a dose of 400 mg? ____________________

What would you tell the parent to give the child a dose in household measurements? ____________________

What volume of medication, in the household measurement system, should be given for an order of 500 mg? ____________________

What is the powder volume in the bottle? ____________________

Introduction

When medications that may require storage over a length of time in liquid form and are unstable, they are often shipped to the pharmacy in powder or crystalline (lyophilized) form requiring reconstitution before administration. Medications such as pediatric antibiotics, injectable antibiotics, or immunization agents are some of the most frequently found medicines in this form. These drugs must have liquid added before their use—liquids in the form of water when the medications are for oral use or in the form of sterile solutions such as sterile water for injection, saline for injection, or diluents supplied by the manufacturer when the medicine is used for parenteral administration. Dissolving the powdered medication in the liquid is called reconstitution.

The dry drug form may be found in single-dose or multidose containers for oral or injectable use. The label on the medication will tell the type of diluent to be used and the amount of the diluent for the desired dosage strength or, in some cases, concentration. The directions on the side of the label should be read carefully to prevent errors in the reconstitution process.

Reconstitution of Powders into Liquid Medications

Medications that are unstable in liquid form for extended periods of time are manufactured in either a powder or crystalline (lyophilized) form for reconstitution before use. To reconstitute a medication, care must be taken to follow the instructions on medication label exactly. Before using the medication, care must be taken that the dry ingredients are completely dissolved or suspended into liquid form by adding a diluent.

When used as an injectable medication, single-dose vials/ampules or multidose vials are available. Available multidose containers are used when a number of doses may be used from the same container within the amount of time that is with the safe time limit after reconstitution. The diluent used for reconstitution for injectable medications must be sterile and may come in a single-dose vial, as for reconstitution of immunizations that are single doses, or in multidose vials such as sterile water for injection used for multiple doses of antibiotics. To reconstitute injectable medications, sterile syringes are used in the appropriate size for the amount of diluent necessary for the manufacturer’s label.

Most oral preparations are found in bottles that are larger than the medication volume present. This allows space for shaking medications before administration. Because the usual vehicle for reconstitution of oral medications is distilled water, graduates are used to measure the quantity of liquid to be added (Figure 9-1). In some pharmacies, a computerized dispenser for distilled water, such as a Fillmaster electronic pharmaceutical water dispenser, is available. When indicating the correct amount of water to be dispensed, this machine provides one half of the necessary diluent, stops and allows time for mixing the powder medication with the diluent, and then dispenses the remainder of the water on demand.

The label on the medication provides the needed information for the necessary volume of diluent to be mixed with the powder to provide the desired dosage per volume. Most oral liquid products are described in dosage strengths that indicate the amount of medication in 1 teaspoonful (5 mL) of medication, whereas the strength described on injectable products varies with the medication and the manufacturer’s instructions based on the intended route of administration. If the medication is a single-strength, single-dose vial, the reconstitution is accomplished by adding the amount of diluent indicated on the label. On the other hand, if the medication vial may be prepared at multiple strengths or concentrations, such as found with antibiotics, the diluent must be adjusted to meet the strength necessary to meet the physician’s order. When reconstituting multiple-strength doses, check the label on the vial for the options available for the route desired and then choose the one closest to that of the physician’s ordered strength for the intended route of administration.

Vials of the same drug may require different volumes and types of diluent for different routes of administration when given parenterally. The directions on the label should be followed exactly to ensure that the correct type and amount of diluent have been used. Some medications may even require specific diluents be added for intramuscular use, such as small amounts of anesthetics to prevent discomfort with administration.

When powders are dissolved in the liquid, the weight or strength of the medication will always remain the same as the amount given on the label. For example, if a label for amoxicillin states that the container holds a total of 2.5 g as a powder, the total weight or strength of the medication will be 2.5 g after reconstitution has occurred. When medications are supplied in dry powder or crystalline form for stability, the space occupied by the powder is known as powder volume or powder displacement. The total liquid volume of the medication will be that of the amount of medication plus the amount of liquid. In the label shown in Figure 9-2, the final volume of the bottle is 100 mL when reconstituted with 78 mL of water (Figure 9-3). So with this reconstitution the powder volume or displacement is 22 mL (100 mL total volume − 78 mL diluent = 22 mL powder volume). Powder volume (Pv) is the difference between the final volume (Fv) and the diluent volume (Dv). This can be shown with the formula Pv = Fv − Dv.