2016. 2. Petunjuk Prakt Blok 21 Dosis

8/17/2019 2016. 2. Petunjuk Prakt Blok 21 Dosis

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1. CALCULATION AND DETERMINATION THE DRUG DOSES

OBJECTIVES

After doing this activity, the students are expected able to:

1. Determine the appropriate dosage regimen (doses, route of administration,

frequency of administration, time of administration, and duration of treatment)2. Calculate the total amount drug needed to fill the prescription

INTRODUCTIONAfter the doctors examine and diagnose the patient, they often prescribe medicine to

relive or cure the diseases. In the writing of a prescription, there are some important thing

that should be paid attention by a doctor to ensure patient safety such as determination the

proper dosing of medication and drug dosage regimen. Drug dosage regimen consists of

route of administration, frequency of administration, doses of each administration, time of

administration, and duration of treatment. Dosing involves a series of steps, that are

1. Find drug dosing guidelines

Dosing guidelines can be found in many common textbook which usually give us a range tochoose from. Some of these ranges may be total daily doses. For instance, the pediatric

dosing guidelines for chloramphenicol (an antibiotic), for meningitis and severe infection,

are 50-100 mg/kg daily in divided doses every 6 hours. Other ranges will be per-dose. The

adult dosing guidelines for cotrimoxazole is 960 mg (trimethoprim 160 mg and

sulfamethoxazole 800 mg) per dose, twice daily. The usual adult intravenous dose of

vincristine sulfate (anticancer) is 1,4-1,5 mg/m2 once weekly, up to a maximum weekly

dose of 2 mg. It use body surface area to create a patient-specific dose.

2. Obtain variable data of patient

After finding drug dosing guidelines, doctors should determine the value of some variables

in which drug dose depends on. The most commonly-used variables are the patient‟s

weight, age, height, or kidney function. To determine the kidney function the data of blood

creatinine (a product of muscle breakdown) concentration is needed.

3. Determine the daily dosing range of patientAfter obtaining dosing guidelines and the value, the next step is: multiply one by the other

in order to get the dosing range for that individual patient. For instance, if the patient is a

child with Body Weight (W) 18 kg who receives chloramphenicol, and based on dosing

guidelines the dose of chloramphenicol for children is 50-100 mg/kg daily, it is simply to

determine that this patient should receive between 900 and 1800 mg of chloramphenicol

daily.

4. Calculate the range for each patient dose

The the drug dose obtained from the reference/guideline is sometimes calculated for 1 day(daily dose). By having a daily dosing guideline, and the patient is to receive more than one

dose per day, it need to divide the total daily dose by the number of doses/day. For instance,

the patient who need to receive between 900 to 1800 mg of chloramphenicol daily should

have this medication divided every six hours or four times per day. It means that the patient

should receive 225 mg to 450 mg in each administration.

We sometimes cannot find any appropriate drug dose which is matched with the strength of

drug available in market (see choose an appropriate strength or concentration). In general,

if we deal with an antibiotic it is better to round up the dosing range. Otherwise, the dose of

other medications should be round down.

5.

Determine an appropriate dosage form for the patient.In order to simplify the drug administration and increase the patient compliance, the dose of

drug has to be converted in „drug dosage form‟ such as tablet, capsule, syrup, suspension,



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etc. Adult patient usually swallow tablet and capsule easier than children. For adult patient

who has an impaired ability to swallow, an alternative dosage form such as liquid is

preferable. The appropriate oral dosage form for children is pulveres (powder) and liquid

(suspension, syrup, etc).

6. Choose an appropriate strength or concentrationAfter drug dose of administration is calculated, we simply look forward for the list of drug

concentration available in market and choose the simplest one. For example,

Choramphenicol suspension is available in a concentration of 125 mg/5 ml. Since patient

needs 250 mg per dose it would be easier to administer 10 ml or two teaspoonful (one

teaspoonful = 5 ml), every six hours.

7. Calculate the total amount needed to fill the prescription.

To calculate the total amount needed to fill the prescription, exact amount of the drug that

will be given per dose/each administration and the duration treatment should be already

determined. Most antibiotics are given for a finite period of time (e.g. 10 days), so if the

patient above is to receive Choramphenicol suspension for 10 days, the amount of

suspension should be prescribed or written in prescription is 400 ml (10 ml/dose x 4doses/day x 10 days). If a bottle contains 60 ml of Choramphenicol, it needs 7 bottles

(400ml/60 ml/bottle = 6,67 bottles 7 bottles) prescribed.

Actual Body Weight (ABW) or total body weight (TBW) is a patient‟s real weight.

Ideal Body Weight (IBW). This is the weight of lean body mass (LBM). It should be

known about this because many medications are dosed based on a patient‟s IBW. Why?

These are medications that do not distribute well into fat (i.e., hydrophilic drugs), and if an

overweight patient is dosed for a such a medication using ABW, it cause overdosing the

patient. The common equation used for calculating IBW is:

Male : 50 kg + (0.9kg)(each cm > 152 cm) = IBW in kg

Female : 45 kg + (0.9kg)(each cm > 152 cm) = IBW in kgExamples of hydrophilic drugs is ampicilline, aminoglycosides (gentamicin, neomycin,

amikacin, tobramycin, andc streptomycin) whereas lipophylic drugs (distribute well into fat)

are methotrexat, fentanyl, thiopental, progesterone, triamcinolone diacetat.

Dosing guidelines in obese adultsTable 1. Examples of drug dosing in obesity

Drug Dosing weight Comment

IBW ABW DW

Ampiciline X Larger volumes of distribution in obese patients

Cyprofloxacine X DW = 0.4 (ABW-IBW) + IBW

Digoxin X

Erythromycine X

Rifampicine X

Theophylline LD MD

Trimethoprim/

Sulfamethoxazole

X DW = 0.4 (ABW-IBW) + IBW

DW – dosing weight for drugs

LD – loading dose

MD – maintenance dose (Source: Semchuk, 2007)

Overweight is defined as a body mass index (BMI) of 25 to 29,9 kg/m2 and obesity as a

body mass index of 30 kg/m2 or more.

BMI = mass (kg)(height (m))2



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Appropriate drug dosing in the obese patient is a challenge for health care practitioners.

Obesity causes physiologic alterations which can affect drug pharmacokinetics. In the obese

patient, body composition is characterized by a relatively higher percent of fat and lower

percent of water and lean tissue mass than the non-obese patient. In spite of increased

cardiac output and total blood volume, the blood flow per gram of fat is less than in the non-

obese patient. Histological hepatic changes and an increased glomerular filtration rate have

also been reported in obese individuals.

Doses for patients with decreased kidney functionMany drugs are cleared by the kidney ( i.e. cleared “renally”). In order to dose medications

cleared by the kidney in patients whose kidneys are not working well, figure out how well

their kidneys are working is needed, then apply that estimation of function to dosing. The

most commonly-used measurement method for determining kidney function utilizes an

endogenous compound called “creatinine”. Identify the patient‟s weight and gender. All of

this information needed to determine a patient‟s “creatinine clearance” (CrCl). CrCl units

are milliliters/minute.Cockroft-Gault equationCrCl = (140 - age) (IBW)

(gender factor)(Scr)

where

· age = age in years

· IBW (Ideal Body Weight) in kg; ABW (Actual Body Weigth = patient‟s real body

weight) can be used when the patient is less than 110% of IBW

· gender factor = 72 for males, 85 for females

·

Scr = the patient‟s serum creatinine in mg/dL

After determining creatinine clearance, use it to follow any given renal dosing guidelines.

Example: A 62 years old, 59 kg, female patient with pneumonia is admitted to hospital and

the decision is made to begin therapy with piperacillin, an antibiotic. Her measured serum

creatinine is 1.4 mg/dL. Standard dosing for patient with good kidneys is 4 gram,

intravenous, every 6 hours (4g IV q6h). This is decreased to 4g IV q8h for patients with

CrCl between 20 and 5 40ml/min, and 4g IV q12h for patients with CrCl < 20ml/min.

Please determine the dosing frequency recommended for this patient.

CrCl = (140 - age) (IBW) = (140 - 62) (59) = 39 ml/min

(85)(Scr) (85)(1.4)

Recommendation: 4g IV q8h

Notice that this patient‟s IBW was used, rather than her ABW, since her ABW was more

than 20% over her IBW. Also notice that the calculated creatinine clearance was rounded

off to the nearest whole number.

Additionally, there are several tools or formula available to adjust a medication dosage for

children.

1. Calculated by considering the doses for adult as reference

a. Based on age:

Fried's Rule for Infants and Children up to 1 to 2 years:



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Child‟s age in months x adult dose (mg)

-------------------------

150

Young's Rule for Children from 1 year to 12 Years:The child‟s age divided by age plus 12 represents the fraction of the adult dose

suitable for the child.

Child‟s age in years x adult dose (mg)

-----------------------

Child‟s age + 12

b. Based on body weight

Clark’s Formula:Clark‟s formula is based upon the weight of the child. To determine the proper

dosage for children, divide child‟s weight in kilograms by 70 kilograms to get the

correct fraction of adult dose.Child‟s weight in kg x adult dose (mg)

-------------------------

70 kg *

*Average weight of an adult is 70 kg

c. Based on Body Surface Area (BSA) Normogram are used to determine the BSA in square meters according to the child‟s

height and weight. When you know the child's BSA, the dosage is determined by

multiplying the BSA by the recommended dose.

Formula for calculating child's dosage based on BSA is

Child's BSA in square meters X adult dose1,73 m2 *

* The figure for the average BSA of an adult in square meters is 1,73.

You can also determine BSA using this formula

BSA = body weight (kg) x height (cm)

3600

2. Calculated by measuring certain physical indicatora. Calculated according to individual BW of the child (.......mg/kgBW)

Example: Doses of Paracetamol 10-15 mg/kgBW/dose b. Calculated according to individual Body Surface Area of the child (mg/m2)

Example: doses of methotrexat 3,3 mg/m2

c. Calculated according to the age of the child

Example: Doses of Paracetamol :

- Age 3 month – 1 year : 60 mg/dose

- Age 1 – 3 year : 60 - 120 mg/dose

- Age 3 – 6 year : 120 mg/dose

- Age 6 – 12 year : 240 mg/dose

Children are more sensitive than adults to medications because of their weight, height,

physical condition, immature systems, and metabolism. The child who weighs more than 50

kg may receive adult dosages. If the calculated dose is greater than the recommended adult

dose, DO NOT administer the medication. A child should not receive higher doses than



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those recommended for the adult, ever. Many drugs have a “do not exceed” or “maximal

dose” in 24 hours listed; this must always be considered.

TOOL AND MATERIAL

-

Questions/scenarios list

-

List of drug dosages

- White Board

- References

PROCEDURE

Method

Each student has to answer the questions below, then present and discuss it with

other student. The answer of each case should contain:

1. Dosage regimen (route of administration, frequency, doses of each administration,

time of administration, and duration of treatment)!

2.

Calculate the total amount drug needed to fill the prescription

The cases are:

1.

A doctor gives erythromycine syrup to Seto, a three-year-old boy (20 kg) suffering

from acute bacterial pharyngitis.

2.

A doctor gives nifedipine capsule to Bp.Juragan, 60 years old having hipertension

3. A doctor gives amoxicillin syrup to Hasan, a one-year-old boy (14 kg) undergoing

uncomplicated pneumonia

4. A doctor gives hydrocortisone cream to be applied topically to Doni, an eight-year-

old boy (27 kg) suffering from atopic Dermatitis.

5.

A doctor gives ranitidine tablet to Ibu Bona, 55-year-old woman suffering

Gastroesophageal Reflux Diseases (GERD)6.

A doctor gives erythromycin tablet to Bp.Zakaria, (65 years old, 160 cm) suffering

acute bronchitis with secondary infection. His creatinin serum is 1,6 mg/dl.

7. A doctor gives ciprofloxacine tablet scored to Ibu Jendela (50 years old, 80kg, 160

cm) suffering uncomplicated urinary tract infection

8. A doctor gives Tempra oral drop to Ja‟far, a five-year-old boy (20 kg) suffering from

fever.

9. A doctor gives chlorpheniramine maleat pulveres to be taken orally to Doni, an one-

year-old boy (10 kg) suffering from allergic Dermatitis.

10. A doctor gives injection Methotrexate to Bayu, a-four-year-old (20 kg, 110 cm)

suffering from Leukaemia

Example of how to answer the case :

A doctor gives Paracetamol to Anggi a one-year-old girl (12 kg), suffering from fever.

Answer :1.

The Dosage regimen :

a. According to reference: oral dosage of paracetamol for children is 10-15

mg/kgBW/dose, given every 4-6 hours. The doses for Anggi with 12 kg BW is

120-180 mg/dose

b.

Route of administration : orally

c. Frequency : every 4-6 hours if necessary (4-6 times daily)

d. Time of administration : before or after meal, because absorption of

paracetamol doesn‟t disturbed with or withoud food

e. Duration of the treatment : 3 days



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2. The total amount drug needed to fill the prescription

Because the duration treatment is 3 days so the amount paracetamol needed is 120

mg/dose x 4 times/day x 3 days = 1440 mg.

a.

Paracetamol comes in a concentration of 120mg/5ml and a bottle

contains 60 ml. It would be easiest to administer 5 ml (one teaspoonful)

four times a day to the child. Because the duration treatment is 3 days so

the amount paracetamol needed is 5ml/dose x 4 dose/day x 3 days = 60

ml or 1 bottle of paracetamol syrup.

b. If the doctor choose powder (pulveres) form and each sachet contain 120

mg, the amount paracetamol to fill in prescription are 1 sachet/dose x 4

dose/day x 3 days = 12 sachet

Duration : 1 x 100 minutes

EVALUATION

Practical laboratory report

REFERENCES

Anonim. 2013. Lesson 4: Calculations used to determine patient- specific doses “The right

dose”. www.courses.washington.edu. Cited 24 June 2014.

Roach, S. 2004. Introductory Clinical Pharmacology. 7th ed.

Robinson, M.J. and Roberton, M.D. 2003. Practical Paediatrics. Ed.5th. Churchill

Livingstone

Semchuk. 2007. Medication Dosing Guidelines in Obese Adults. RQHR Pharmacy Services

Suharmi, S dan Murini, T. 2009. Bentuk sediaan Obat. Bagian Farmasi Kedokteran,

Fakultas Kedokteran , Universitas Gadjah Mada.

Syarif, R. A., Murini, T., Wahyuningsih, M. S. H. 2012. Pedoman Dasar Penulisan Resep Dokter untuk Anak . Bagian Farmakologi dan Terapi Fakultas Kedokteran

UGM, Yogyakarta

http://www.courses.washington.edu/





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LIST OF DRUG DOSAGES

AMOXYCILLIN

Dosage orally:Children : 10-25 mg/KgBW/dose

Adult : 250-500 mg/doseEvery 8 hoursDuration of treatment uncomplicated pneumonia : 7-10 days

Drug preparations available on the market:1. Generic name:

- Capsul 250 mg; 500 mg

- Dry syr. 125mg/5ml (60 ml/flask)

- Dry syr. Forte 250mg/5ml (60 ml/flask)2. Brand name : Amoxan

- Capsul 250 mg; 500 mg- Dry syr. 125 mg/5ml (60 ml/flask)

- Dry syr. Forte 250 mg/5ml (60 ml/flask)

ACETAMINOPHEN

Dosage orally:Children : 10-15 mg/kg/doseAdult : 500-1000 mg/doseEvery 4-6 hoursMaximal dose : 4 g/day (Dewasa)

Drug preparations which are available on themarket:Raw materialGeneric name:

- Tablet 100 mg; 500 mg- Syr. 120mg/5ml (60ml/flask)

Brand name : Tempra

- Oral drop 80 mg/0,8ml (15 ml/flask)

- Syrup 160 mg/5 ml (60 ml/flask)

CHLORPHENIRAMIN MALEAT

Dosage orally:Children : 0.1 mg/kg BW/dose

Adult : 4 mg/dose.Every 6-8 hours

Duration of treatment: 5 days

Drug preparations available on the market:1. Raw Material

2. Generic name: Tablet 4 mg3. Brand name :Alleron

capl 4 mg.

CYPROFLOXACINE

Adult oral dose: 250 to 750 mg twice dailyTablet may delayed by the presence of food, but is not substantially affected overall.

Duration of treatment uncomplicatedurinary tract infection: 3 days

For renal impairmentCC 30 to 50 mL/minute: up to 500 mg by

mouth every 12hours or the usual dose byintravenous infusion• CC 5 to 29 mL/minute: up to 500 mg bymouth every 18 hours or up to 400 mg byintravenous infusion every 18 to 24 hours

given over 30-60 minutes as a solutioncontaining the equivalent of 1 to 2 mg/mL.

Drug preparations available on the market:Generic

- Tablet scored 500 mg

- Infusion 2 mg/mL (100ml/bottle)

---------------------------------------------------------------------------------------



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Equivalent AUC Dosing RegimensCipro Oral Dosage Equivalent Cipro IV Dosage

250 mg Tablet q 12 h 200 mg IV q 12 h500 mg Tablet q 12 h 400 mg IV q 12 h

750 mg Tablet q 12 h 400 mg IV q 8 h

------------------------------------------------------------------------------------------

ERYTHROMYCIN

Dosage orally:Children : 10 mg/kg BW/doseAdult : 250-500 mg/doseUsual IV dose for adult: 250-500 mg q6h.

Max 4 g/dayFrequency : every 6 hoursThe dose of erythromycine in renal failure is

decreased to 50-75% of normal dose (maxdaily dose = 2 g) for patients with CrCl <10ml/minDuration of treatment acute pharingitis: 10

daysDuration of treatment pneumonia: 14 days

Drug preparations available on the market:1. Generic name:

- Capsul 250 mg; 500 mg.- Dry syr 200mg/5 ml (60ml/flask)

2. Brand name : Erysanbe

- Caplet 500 mg; Capsul 500 m- Chewable 200mg

- Dry syr 200 mg/5ml (60 ml/flask)

HYDROCORTISONE

Dosage: 0,5- 1,0%Every 6-12 hours.

Duration of treatment for dermatitis : 7-14 days

Drug preparations available on the market:1. Raw Material

2. Generic name:- Cream 1,0% (5g/tube)

- Cream 2,5% (5g/tube)

3. Brand name : Cortine



METHOTREXATE

A common dose for maintenance therapy ofacute lymphoblastic leukaemia is 15 mg/m

2

once or twice weekly, orally or intramuscularly,

with other agentssuch as mercaptopurine

Duration of treatment: 6 months

Drugs.comUsual Pediatric Dose for Acute LymphocyticLeukemia 100 mg/m2 over 1 hour followed by a

35 hour infusion delivering 900 mg/m2/day

Usual Pediatric Dose for Neoplastic Diseases7.5 to 30 mg/m2 IM or orally every 2 weeks.Alternate dosing: 10 to 18,000 mg/m2 IV bolus

or continuous infusion over 6 to 42 hours.

Drug preparations available on the market:1. Generic Name:

- Tablet 2,5 mg

- Dry injection 50 mg/2ml (vial 2ml)

- Dry injection i.v./i.m. 5mg/2 ml (vial 2 ml)2. Brand name : Methotrexate DBL

- Injection Methotrexate 5mg/2ml (vial 2 ml)

- Injection Methotrexate 50mg/2ml (vial 2ml)



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Usual Adult Dose for Acute LymphoblasticLeukemiaInduction: 3.3 mg/m2/day orally or IM (incombination with prednisone 60 mg/m2).

Maintenance (during remission): 15 mg/m2 IMor orally twice a week.Alternate remission dosing: 2.5 mg/kg IV every14 days.

NIFEDIPINE

Dosage orally:10 to 40 mg twice dailyDuration of treatment for hipertension: initialdose for 7 days followed 1 month

Drug preparations available on the market:1. Generic Name:

- Capsule 10 mg

- Slow release tablet 20 mg and 30 mg2. Brand name : Adalat

- Tablet 5 and 10 mg

RANITIDINE

Adult:In gastro-oesophageal reflux disease theoral dose is 150 mg twice daily or 300 mg at bedtime for up to 8 weeks or, if required, 12

weeks.Duration of treatment for GERD: 2 weeks

Drug preparations which are available on themarket:1. Generic name:

- Tablet 150 mg2. Brand name :Rantin tablet 150 mg dan 300 mg



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Source : Roach (2004)



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Source : Roach (2004)

2016. 2. Petunjuk Prakt Blok 21 Dosis

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