Interpreting Physicians’ Orders for Dosages

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Chapter 14

Interpreting Physicians’ Orders for Dosages

Objectives

• Calculate total dosage of medication when quantity is unknown

• Calculate number of doses of medication from total dosage presented on a prescription

• Calculate the number of doses in a prescription if medication is taken according to a physician’s order, including duration in days

• Read and interpret prescriptions to calculate doses and dosages

Pretest

Using the information provided, calculate the doses or dosages for the prescriptions as appropriate. Note that all doses will be administered on the first day as ordered unless otherwise stated. Note that a month means 30 days unless otherwise stated. Round answers to measurable doses depending on the utensil to be used or the available form of medication. Show your work.

image 1 A physician prescribes amoxicillin suspension 250 mg/5 mL 150 mL to be taken 1 teaspoonful three times a day until the entire amount has been taken. A dosespoon is to be included with the prescription.

image image 2 A physician prescribes furosemide 20 mg po daily × 1 mo image refills × 2. The available medication is furosemide 40 mg/tablet.

image 3 Using the provided prescription, how many tablets are necessary to fill the prescription? __________

image 4 A physician prescribes NPH insulin 80 units qam. The vial contains 10 ml of NPH insulin U-100. Indicate the amount of medication on the syringe so that you can supply patient instruction for self-administration.

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image 5 An order is written for the preparation of CEFTIZOXIME 500 mg in 50 mL of D-5-W to be infused at the rate of 50 mg/kg per day. CEFTIZOXIME is available for dilution at 1 g/10 mL of sterile water.

image 6 A physician prescribes Vibramycin 100 mg po tab ii stat and repeat in 12 hours. The prescription then reads to provide the patient with 100 mg/d for one week.

image 7 A physician orders AMPICILLIN 0.2 g/kg/d IV in divided doses q6h. The physician wants AMPICILLIN 500 mg to be added to each 100 mL of D-5-W. AMPICILLIN is available in 500 mg vials for reconstitution with 1.2 mL of diluent. The patient weighs 110 lb.

image 8 Use the prescription provided to make the necessary calculations. The tablet is available as Toprol-XL 25 mg.

image 9 A patient weighing 198 lb is to receive chloramphenicol 50 mg/kg/d in divided doses q4h to be administered in D-5-NS 500 mL for a Salmonella typhi infection. The available medication is in 1-g vials at 100 mg/mL.

image 10 A child has a streptococcal infection of the throat. The child weighs 66 lb. The physician tells the pharmacist to supply the accurate amount of medication so that the child receives erythromycin 40 mg/kg/day in divided doses to be administered q6h for 10 days. The medication is available as erythromycin 200 mg chewable tablets.

What would the prescription label read for the prescription with the medication shown as available? __________

If the parent states that the child will not chew the tablet but will take oral liquids, after obtaining the physician’s permission, what volume of medication would be supplied to the child with each dose if the erythromycin is available as 400 mg/5 mL? __________

How would the label read in household measurements? __________

How many tablets would be necessary to complete the order if chewable tablets are used? __________

How many milliliters of medication would be used to prepare the prescription? __________

Using a choice of utensils for dispensing with the medication, what utensil should be chosen for more exact administration of the medication at home? __________

Hint: Go back to Chapter 7 to see available utensils.

image 11 The patient presents the provided prescription for preparation. The patient has no drug insurance coverage and wants 2 months’ supply. The prescription has prn refills for one year. The medication is available in 40-mg capsules.

image 12 A physician prescribes amoxicillin 62.5 mg po tid for 10 days for a child weighing 44 lb. Available is amoxicillin 125 mg/5 mL in 100-mL and 150-mL containers.

image 13 A physician writes a prescription for Humulin N 65 units subcutaneously qam and qpm. The prescription also contains an order for Humulin R 25 units subcutaneously with the afternoon dose.

image 14 A physician prescribes atenolol 75 mg po qam and 25 mg po at bedtime. The available stock medication is atenolol 50 mg.

image 15 A physician prescribes ibuprofen liquid 10 mg/kg to be administered po qid prn for pain for a child who weighs 66 lb. The available medication is 100 mg/5 mL. The volume of medication to be dispensed is 8 ounces.

Preparing Medications When The Quantity For Dispensing Is Unknown

In some cases physicians may accidentally write orders for the dispensing of medications and do not include the amount of medication that should be dispensed. In those cases the pharmacy staff is responsible for ensuring that the patient has sufficient medication to complete the desired medication cycle. The formula for calculating the total dose quantity required follows:

< ?xml:namespace prefix = "mml" />Total dosage required=Number of doses per day×Total number of days

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Example 14-1

imageA physician prescribes digoxin 0.125 mg tab ii stat then tab i daily. How many tablets would be necessary for a 30-day supply if the available medication is that seen on the following label?

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Total dosage necessary=2 tablets now and 1 tablet daily for 29days

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Total dosage necessary=2 tablets+29 tablets

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Total dosage necessary=31 tablets

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Prescription label directions: Take two tablets now then one tablet daily

Practice Problems A

Calculate the following problems, showing all calculations. Note that a month means 30 days unless otherwise stated.

1. imageA physician prescribes phenobarbital gr image po q6h for epilepsy. The order is to provide a month’s supply with each prescription refill.

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2. imageA physician prescribes Voltaren 50 mg po tid with meals or snack. How many tablets are necessary to fill this prescription for a month? __________

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3. imageA physician prescribes cephalexin oral suspension 62.5 mg po q6h × 10 days. Indicate the dose on the available utensil below.

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4. image imageA physician prescribes Macrodantin 0.1 g to be given po qid for a month for a severe urinary tract infection.

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5. imageUsing the provided prescription, how many tablets would be necessary to fill the prescription? __________

6. imageUsing the provided prescription, what volume of medication must be supplied to fill the order? __________

7. imageDuring a severe influenza epidemic, the physician writes the provided prescription as a prophylactic in an older adult with COPD. The only amoxicillin in stock is amoxicillin 250 mg/capsule.

8. imageUsing the provided prescription, what volume of medication must be provided to fulfill this order? __________

9. imageA patient presents the provided prescription for preparation. __________________

10. imageOn Friday a nurse orders medication to be sent to the floor for the weekend using the provided medication label. The patient is to receive cimetidine 300 mg IM q6h.

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11. imageA physician orders Solu-Cortef 150 mg IM q8h for a patient with severe allergic dermatitis.

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12. imageA physician prescribes cyanocobalamin 1.5 mg subcutaneously for administration twice a week for a month. Use 4 weeks for a month with this calculation.

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13. imageA physician prescribes Keflex 500 mg to be given po qid.

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14. imageHow many tablets would be necessary to supply this medication for 2 weeks? __________

15. imageHow many tablets are necessary for a month’s supply of the provided prescription? __________

16. imageThe physician orders phenobarbital gr 1/4 po q8h for seizures.

17. Four prescriptions are written as shown in the provided illustration. Determine how many tablets of each medication would be necessary for the prescription as written.

image

image Depakote 500-mg tablet is available.

Depakote to be supplied: __________

Interpret the order for this medication. ____________________________________________

Indicate label directions. __________________________________________________________

image Desyrel 50-mg tablet is available.

Desyrel to be supplied: __________

Interpret the order for this medication. ____________________________________________

Indicate label directions. __________________________________________________________

image Xanax 0.5-mg tablet is available.

Xanax to be supplied: __________

Interpret the order for this medication. ____________________________________________

Indicate label directions. __________________________________________________________

image Zoloft 100-mg tablet is available.

Zoloft to be supplied: __________

Interpret the order for this medication. ____________________________________________

Indicate label directions. __________________________________________________________

* These abbreviations are found on the TJC Do Not Use List and ISMP’s List of Error-Prone Abbreviations, Symbols, and Dose Designations due to medication safety issues. They should not be used. You are being tested on them here because these abbreviations may still appear in the pharmacy setting.

18. imageA physician prescribes Cardizem 120 mg qid.

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19. imageA patient who has difficulty swallowing tablets is to receive Mellaril 45 mg bid.

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20. image imageA physician prescribes Lasix 80 mg po stat, then Lasix 40 mg po daily thereafter.

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Calculating The Number of Medication Doses In A Given Container

Some physicians write prescriptions to last a specified amount of time. If the size of the dose and the amount of medication in a container is known, the number of doses in the container can be calculated to ensure the patient has a sufficient amount of medication for the expected time for administration. To calculate this information, the following formula should be used:

Number of doses in a container=TotalamountofmedicationincontainerDosesize

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Tech Note

Calculations of doses of medication must have the same measurement system in the numerator and denominator.

Example 14-2

A physician orders a dose for 1 tsp of an antibiotic from a bottle containing 120 mL.

Notice that a teaspoon is in the household measurement system and milliliter is in the metric system, so a conversion to a common measurement system must be performed. The first step is to convert the 1 tsp to 5 mL. Now you can do the necessary calculation.

image

image

The number of doses in the container=120÷5

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Number of doses=24

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Does the container of medication contain adequate doses for 10 days if the medication is given tid?

The amount of medication per day is 15 mL or 3 doses. To last 10 days, there must be 30 doses, so the amount of medication provided is not adequate for the ordered amount because 24 doses are available and 30 doses are needed.

Practice Problems B

In the following problems, determine the number of doses in the container. Note that a month means 30 days unless otherwise stated. Show your work.

1. imageHow many full doses are available with this prescription? __________

* These abbreviations are found on the TJC Do Not Use List and ISMP’s List of Error-Prone Abbreviations, Symbols, and Dose Designations due to medication safety issues. They should not be used. You are being tested on them here because these abbreviations may still appear in the pharmacy setting.

2. imageA physician prescribes Keflex Suspension 125 mg q6h for 10 days.

image

3. image imageA patient is to take furosemide 80 mg po daily.

image

4. imageA physician orders Humulin 70/30 63 units subcutaneously daily.

image

5. imageA physician orders EryPed 200 mg qid for a child with acute bronchitis.

image

6. imageA physician desires that a patient receive heparin 2500 units IV q8h. The vial of medication available is shown as follows.

image

7. imageHow many doses of medication are in this prescription? __________

* Per ISMP’s List of Error-Prone Abbreviations, Symbols, and Dose Designations, the abbreviation “cc” should not be used. It is included here because it may still be seen in a pharmacy setting.

8. imageA physician prescribes Halcion 0.25 mg hs prn sleep.

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9. imageA physician prescribes rifampin 600 mg daily 1 hr ac for tuberculosis.

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10. imageA physician orders digoxin 0.25 mg stat and in am and then digoxin 125 mcg daily.

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11. imageA physician orders Procanbid 1 g stat and repeat in 30 min. Then give Procanbid 500 mg q12h as a maintenance dose to control atrial fibrillation.

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12. imageA physician orders Lopid 600 mg qam and 300 mg qpm.

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13. image imageA vial of Compazine with the provided label has been provided to the medical floor for a patient with postoperative emesis.

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14. imageUsing the provided prescription, the pharmacist supplies 50 mL of the medication on the prescription. The dropper holds 1 mL. Round to whole doses.

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15. imageAs the pharmacy technician, you are checking the floor narcotics for the amount of meperidine that has been administered. Meperidine 50 mg has been given to four patients over the past 24 hours. The floor stocks a box of 75 mg/mL ampules in a floor locked cabinet, as labeled below.

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16. imageUsing the provided prescription, how many doses of Brovex would be supplied to the patient? __________

17. imageHow many doses of amoxicillin are found with this prescription? __________

18. image imageThe physician prescribes ibuprofen 0.8 g tid pc for a patient with osteoarthritis.

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19. imageA physician prescribes amoxicillin 250 mg to be taken tid.

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20. imageA physician orders Lincocin 0.6 g IM q12h.

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Determining The Length Of Time A Prescription Will Last

In some cases it is important to calculate how long the medication prescription will last if taken appropriately. In today’s market, where insurance claims may be submitted only after a specified period of time following the last prescription dispensing, the pharmacist or pharmacy technician needs to know if the medication has been taken properly or if the medication should be refilled at the specific time.

image Tech Alert

If the proper length of time between prescription refills is inappropriate, the pharmacist should be notified that the prescription cannot be refilled. The pharmacist then notifies the physician for further directions and so patient education can occur by both the pharmacist and physician to be sure medications are being administered as ordered.

The time that the prescription should last may be determined using the following equation:

Total dose administration time=TotalamountofmedicationNumberofdosestobeadministeredinaspecifictime

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Example 14-3

A physician orders 60 tablets of antibiotic to be administered qid. How many days will the prescription last if taken properly?

Total dose administration time=TotalamountofmedicationNumberofdosestobeadministeredinaspecifictime

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Total dose administration time=60tablets4tablets/day

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image

Total dose administration time=15 days

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Tech Note

Again, be sure the medication measurements in the numerator and denominator are the same. If not, make the needed conversion calculations.

Practice Problems C

Complete the following problems, showing all calculations. Note that a month means 30 days unless otherwise stated. Calculate as full days unless otherwise stated.

1. image How long would the provided prescription last? __________

2. imageHow long would the medication in the provided prescription last? __________

3. imageA physician writes a prescription for minoxidil 0.04 g to be administered po daily. The pharmacist fills the prescription with 40 tablets of the medication shown on the provided label.

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4. imageA physician writes a prescription for Lanoxin 0.125 mg tablets #40. The patient is to take Lanoxin 0. 5 mg stat and 0.375 mg in am and then to take tab i daily.

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5. imageUsing the provided prescription, how long would the medication last? _________

6. imageHow long would the medication in the provided prescription last if taken appropriately? __________

7. imageA physician prescribes erythromycin ethylsuccinate 200 mg tid using the label provided.

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8. imageHow long would the provided prescription last if taken appropriately? __________

9. imageHow long would the provided prescription last if taken appropriately? __________

10. imageHow long would this medication last if taken as specified on the provided prescription? __________

11. imageHow long would the provided prescription last if taken appropriately? __________

12. imageA physician prescribes Humulin R 50 units subcutaneously at breakfast and 40 units subcutaneously before the evening meal.

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13. imageA physician prescribes penicillin G potassium 200,000 units bid. The medication has been diluted with 1.6 mL of diluent.

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14. imageA physician prescribes 200 mg of Lorabid po bid.

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15. imageA physician prescribes Dilantin 0.3 g to be taken po each am and Dilantin 100 mg to be taken po at bedtime for epilepsy.

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16. imageA physician prescribes Prozac Liquid 40 mg po qam.

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17. image imageA physician prescribes Benadryl elixir 18.75 mg po tid.

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18. imageA physician prescribes Biaxin 500 mg po bid. The available medication is shown on the provided label.

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19. imageThe physician prescribes KCl 80 mEq po qam. The medication is supplied in the container with the provided label.

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20. imageA patient is to take Lantus insulin 35 units qam. Using the syringes below, show the amount of Lantus to be administered on the correct syringe for the order.

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Review

In some cases, pharmacists may be asked to calculate the amount of medication to be dispensed when the number of doses per day and the number of days for treatment is known. On other occasions, the calculation of the number of doses of medications in a container may be necessary to ensure the patient has adequate medication to complete the prescription or physician’s order. Finally, for refills and occasionally when insurance companies have restrictions on the amount of medication that can be dispensed at a given time, you may be required to determine just how long the medication will last. All of these tasks may be necessary to accurately dispense medications and calculations of the time must be accomplished.

Posttest

Before taking the Posttest, retake the Pretest to check your understanding of the materials presented in this chapter.

Use the correct technique to complete the following calculations. A month is 30 days unless otherwise stated. As always, show your calculations. All calculations should be for full days.

image 1 Determine the number of tablets necessary to fill this prescription. __________

* These abbreviations are found on the TJC Do Not Use List and ISMP’s List of Error-Prone Abbreviations, Symbols, and Dose Designations due to medication safety issues. They should not be used. You are being tested on them here because these abbreviations may still appear in the pharmacy setting.

image 2 Determine the number of tablets necessary to complete the provided prescription for 30 days. __________

image 3 How many Alora patches are necessary for a 30-day supply? __________

image image image 4 A physician writes a prescription for a 1 : 1 : 1 proportion of the following:

image 5 A physician writes a prescription for Decadron as shown on the provided label on a sliding scale of tabs 1 qid × 2 days, tid × 2 days, bid × 2 days, and daily × 4 days.

image

image 6 How many days would the provided prescription last if the medication is taken as written? __________

* Per ISMP’s List of Error-Prone Abbreviations, Symbols, and Dose Designations, “qd” should not be used. It is used here because it may still be seen in the pharmacy setting.

image image 7 How long would the prescription for Gabitril last if taken appropriately? __________

image 8 How long would the provided prescription last if taken as ordered? __________

image 9 A physician orders erythromycin ethylsuccinate 300 mg po tid for 10 days.

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image 10 A physician writes an order for Voltaren 50 mg bid with food for 7 days and decrease to daily for a 30 day supply.

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image 11 If the patient uses the albuterol as ordered on a regular basis and does not skip a dose, how long would the provided medication last? __________

image 12 How many capsules would be necessary to provide a 3-month supply? __________

image 13 A physician orders Coumadin 5 mg po on Sunday, Tuesday, Wednesday, Friday, and Saturday and Coumadin image mg po on the other days of the week.

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image 14 If the patient takes the medication as ordered at one tablet q4h, as well as before an appointment, how many days would this medication last? __________

image 15 How many days would the provided prescription last if taken as written? ___________

image 16 The medication as prescribed is available in a 5-mL container.

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image image 17 How many doses of the medication are found in the provided prescription as ordered? _________

image 18 A physician prescribes Dilantin 200 mg po bid for 14 days.

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image 19 A physician writes for Thorazine 50 mg po qam and 75 mg po at bedtime.

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image 20 How long would the provided medication last if taken as ordered? _________

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