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?

image

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

image

Total dosage necessary=2 tablets+29 tablets

image

Total dosage necessary=31 tablets

image

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.

image

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.

image

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

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