Prescription Writing for Drugs in Solid Forms

Computation of Dosages and Prescription Writing

for Liquid Forms and Parenterally-Administered

Drugs

SOLIDS – Case # 1:For the treatment of gastritis in a male executive, Famotidine tablet (available in 20- and 40-mg tablets) to be given orally at a dose of 40 mg per

day at bedtime for 4 weeks. Compute for the number of tablets to be given per dose.

40-mg tablet/ 20-mg tablet = 2 tablets 40-mg tablet/40-mg tablet = 1 tablet

Compute for the number of tablets to be given for the whole course.

2 20-mg tablets x 28 days = 56 tablets 1 40-mg tablet x 28 days = 28 tablets

Prescribe: Patient’s Name, Address, Age, Date

RxFamotidine 40 mg

tablet # 28

Sig.: Take 1 tablet once daily at bedtime for 4 weeks.

MD’s Name and Signature, License #, PTR #

SOLIDS – Case # 2: Nifedipine capsules, available in 5- and 10-mg capsules, to be taken orally at a dose of 5 mg

3x a day for 14 days.

Compute for the number of capsules to be given per day. 1 5-mg capsule per dose x 3 doses per day = 3 5-mg

capsules per day Compute for the number of tablets to be given for the

whole course. 3 capsules x 14 days = 42 5-mg capsules

Prescribe: Patient’s Name, Address, Age, Date

RxNifedipine 5 mgcapsule # 42

Sig.: Take 1 capsule 3 times a day for 14 days.

MD’s name/signature, License #, PTR #

LIQUIDS: 2 STEPS INVOLVED IN PEDIATRIC DOSAGE

CALCULATIONS Determine whether or not the dose is

within a safe range. Calculate the minimum and maximum levels

for normal daily doses. Divide by the number of doses in a 24-hour

period.

Calculate for the amount to be prescribed and administered. Desired quantity x Dose available x Conversion

factor = Amount to be administered

CASE 1: An 18-kg child needs to be given Amoxicillin suspension at a dose of 20-40 mg/kg/day in 3

divided doses for 7 days. Amoxicillin is available in 60-ml bottles, 125 mg/5 ml strength. Compute for

the dose in household measure and write a prescription that includes the number of bottles

needed for the whole course of therapy. For the minimum dose:

20 mg/kg/day x 18 kg = 360 mg/day 24 hrs/day doses/day = 8 hours interval between

doses mg/day ÷3 doses/day = 120 mg/dose or every 8

hours

For the maximum dose: 40 mg/kg/day x 18 kg = 720 mg/day 720 mg/day ÷ 3 doses/day = 240 mg/dose or every 8

hours

Normal range is: 120 – 240 mg/dose or every 8 hours

Case 1

The desired quantity. 120 mg The dose available. 120 mg x 5 ml

125 mg Conversion factor. 120 mg x 5 ml x 1 tsp

125 mg 5 ml Set up the formula using “X”. X = 120 mg x 5 ml x 1 tsp

125 mg 5 ml Cancel out all like measurements. X = 120 mg x 5 ml x 1 tsp

125 mg 5 ml Multiply across the tops and bottoms of the fractions. X = 120x5x1

tsp 125x5

Divide. X= 600 tsp ÷ 625 Assess your answer and double-check your math. X = 0.96 tsp or 1

tsp

Case 1

Compute for the number of bottles needed for the whole course of therapy:

60 ml ÷ 5 ml = 12 tsp7 days x 3 doses/day = 21 doses = 21 tsp21 tsp ÷ 12 tsp/bottle = 1.75 bottles or 2 bottles

Prescribe: Patient’s Name, Address, Age, Date

RxAmoxicillin 125 mg/5 ml suspension

bot # 2 60 ml-bottle

Sig.: Take 1 teaspoon orally every 8 hours for 7 days.

MD’s Name/Signature, License #, PTR #

Case 2: For the symptomatic relief of cough in a 7-year-old patient who weighs 20 kg, you prescribe Ambroxol syrup at a dose of 1.2 mg/kg/day in 2

divided doses for 5 days. The drug is available in 15 mg/5 ml strength and in 60-ml bottle.

The desired quantity. 20 kg x 1.2 mg/kg/day = 24 mg/day 24 mg/day ÷ 2 doses/day = 12 mg/dose

The dose available. 12 mg x 5 ml (No conversion factor) 15 mg

Set up the formula using “X”. X = 12 mg x 5 ml 15 mg

Cancel out all like measurement units. X = 12 mg x 5 ml 15 mg

Multiply across the tops and bottoms. X = 12 x 5 ml 15

Divide. X = 60 ml ÷ 15 Assess your answer and double-check your math. X = 4

ml/dose

Case 2

Compute for the number of bottles needed for the 5-day course: 60 ml ÷ 4ml/dose = 15 doses per bottle at 4 ml/dose5 days x 2 doses/day = 10 doses needed10 doses ÷ 15 doses/bottle = 0.67 bottle or 1 bottle

Prescribe: Patient’s Name, Address, Age, Date of Prescription

RxAmbroxol 15 mg/5 ml syrup

bot # 1 60-ml bottle

Sig.: Take 4 ml by mouth every 12 hours for 5 days.

MD’s Name/Signature, License #, PTR #

ASSIGNMENT

Write a complete prescription for the following patients (please include your computation):

A 2-year-old child with fever, weighing 8 kg, who needs Paracetamol syrup, available at a strength of 120 mg/5ml, given at a dose of 15 mg/kg/dose every 4 hours PRN for temperature of 37.8oC and over. Paracetamol is available in 60-ml or 120-ml bottles.

A 7-year-old child, who weighs 20 kg, with Pneumonia needs Azithromycin suspension at a dose of 10 mg/kg/day on day 1 and 5 mg/kg/day on days 2-5, given only once daily. The drug is available in 15-ml bottles, 200 mg/5 ml strength.

ASSIGNMENT

Write a complete prescription for the following patients (please include your computation):

For intestinal parasitism of a 25-kg girl, using Pyrantel pamoate at a dose of 10 mg/kg/day, given once a day for 3 days. The drug is available in suspension form with a strength of 125 mg/5 ml in 30-ml bottle.

For the treatment of uncomplicated mild pneumonia in a 10-month-old infant weighing 20 lbs., using Cefalexin at a dose of 50 mg/kg/day in 3 divided doses for 7 days. The drug is available only as infant drops with a strength of 100 mg/ml in 10-ml bottle.

Injectables: Case 3 - A 27-year-old male with primary syphilis for whom you prescribe Penicillin at

a single dose of 2.4M International Units (MIU) by IM, injected after a negative skin test. The drug is

available in 1.2MIU 1-ml vial.

The desired quantity. 2.4 MIU The dose available. 2.4 MIU x 1ml

1.2 MIU Set up the formula using “X”. X = 2.4 MIU x

1ml 1.2 MIU

Cancel all like measurement units. X = 2.4 MIU x 1ml 1.2 MIU

Multiply across the tops and bottoms. X = 2.4 x 1ml ÷1.2

Divide. X = 2.4 x 1ml ÷1.2 Assess your answer and double-check your math. X = 2 ml

Case 3 Compute for the number of vials:

2.4 MIU ÷ 1.2 MIU/vial = 2 vials Prescribe: Patient’s Name, Address, Age, Date of

PrescriptionRx

Penicillin 1.2 M International Unitsvial # 2 1-ml vial

Sig.: Inject 2 ml intramuscularly single dose after a negative skin test.

MD’s Name/Signature, License #, PTR #

MEDICATION ORDER: Penicillin 2.4M IU, single dose, IM, ANST.

9-11-07

4:00pm

Case 4: A 30-kg male is admitted for meningitis and you prescribe Ceftriaxone injectable (Forgram) at a dose of 50 mg/kg/day given every 12 hours by slow

IVTT for 10 days. The drug is available in 500-mg-vial with 5-ml

diluent. The desired quantity. 30 kg x 50 mg/kg/day ÷ 2 doses/day

1,500 mg/day ÷ 2 doses/day = 750 mg/dose The dose available. 750 mg/dose x 5 ml

500 mg Set up the formula suing “X”. X = 750 mg/dose x 5 ml

500 mg Cancel all like measurement units. X = 750 mg/dose x 5 ml

500 mg Multiply across the tops and bottoms. X = 750 x 5 ml ÷ 500

mg Divide. X = 3,750 ÷ 500 Assess your answer and double-check your math. X = 7.5

ml/dose

Case 4 Compute for the total number of vials needed for the 10-day

course of therapy.750 mg/dose ÷ 500 mg/vial = 1.5 vials/dose1.5 vials/dose x 2 doses/day x 10 days = 30 vials for the 10-day course

Prescribe: Patient’s Name, Address, Age, Date RxCeftriaxone injectable (Forgram)vial # 30 500-mg vial with 5-ml diluent

Sig.: Inject 7.5 ml slow IVTT every 12 hours for 10 days ANST (after a negative skin test).

MD’s Name/Signature, License #, PTR #MEDICATION ORDER:

Ceftriaxone injectable (Forgram) 7.5 mL by slow IVTT q 12o

x 10 days ANST.

Assignment

Compute and write a complete prescription for the following patients:

Valium injectable for a 5-month-old 7-kg infant, having convulsions. Its dosage is 0.1-0.3 mg/kg/day administered by IVTT every 8 hours. It is available in 10-mg/2-ml ampule.

For acute pulmonary congestion in a 55-year-old male using Furosemide at an intravenous dose of 40 mg initially, followed by 2 more doses at 20 mg/dose with an interval of 12 hours between doses. The drug is available in 20-mg/2-ml ampule.

Assignment

Compute and write a complete prescription for the following patients:

Ceftriaxone (Rocephin) IV vial for a 6.5-lb neonate at a dose of 30 mg/kg/day, given once daily for 5 days by slow IVTT. It is available in 250-mg IV vial.

A 42-year-old woman, weighing 52 kg, is admitted with cerebral edema associated with a malignancy. You contemplate on giving Dexamethasone injectable at a dose of 0.5 mg/kg/day in 4 divided doses for 3 days. The drug is available in 4-mg/ml 2-ml vial.

TOPICAL PREPARATIONS

For acute bacterial conjunctivitis, OD: Chloramphenicol (Spersanicol) eye drops 1 gtt to the affected eye 2 hourly for 1 day, then QID x 3 days.

For atopic dermatitis:Betamethasone valerate (Betnovate) cream to be applied thinly on skin lesions 2x a day for 5 days.