Drug Dose Calculations & Timing

Mohammad M. Kamal Nawar

Steward of Clinical Pharmacy Department

& Drug Information Center

ERMED

Minstry of Transport

2011 – 2013

2 By : Dr. Mohammad M. Kamal Nawar

Drug Dose Calculation

There are 3 types of measurements you will encounter تواجهها when

dealing with medications :

Type Number Solids Liquids

Imp

eri

al S

yste

m

Household ًمنزل Whole numbers & fractions before الكسور unit . e.x. 11/2 T

Teaspoons ( tsp , t ) Tablespoons ( Tbs , T ) Pounds ( lb ) باوند ، رطل

Drop ( gtt ) Ounce ( oz ) أونص ، أوقٌة

Cup ( c ) Pint ( pt ) نصف

لتر

Quart ( qt ) ربع

جالونGlass

Apothecary صٌدالنً

Whole numbers , fractions & roman numerals after unit , e.x. gr 151/2 , or dr iss

Grains ( gr ) Drams ( dr ) دراخمة

Minum ( m ) Fluid drams ( dr )

Syst

em

Inte

rnat

ion

ale

( S

. I )

Metric المتري Whole numbers & decimals األرقام

before العشرٌةunit . e.x. 0.15 ml

البد من : مالحظة كتابة الرقم صفر

قبل العالمة العشرٌة

Grams ( g ) Meter ( m )

Liters ( L )


Common conversion factors

1 cc ( cubic centimeter ) = 1 mL = 15 gtt = m 15

dr 1 = 4 mL

1 T = 3 t = 15 mL

1 oz = 30 mL = dr 8

gr 1 = 60 mg

1 gr = gr 15

1 in ( inch ) = 2.54 cm

1 kg = 2.2 lb

Roman numerals

1/2 = iss

1 = I or i , 2 = II or ii , 3 = III or iii

4 = IV or iv ( i before v = 5-1 )

5 = V , 6 = VI , ....

9 = ix , 10 = x , 11 = xi , ....

19 = xix ( = 10 + ( 10-1 ) ), 20 = xx

Kilo Unit Milli Micro

Kilogram Gram Milligram Microgram Kiloliter Liter Milliliter Microliter

Kilometer Meter Millimeter Micrometer 1 1000 1000000 1000000000


Body Surface Area ( BSA ) ( m2 )

.glomerular filtration rate ( GFR ) و renal clearanceتأتً أهمٌته فً حساب

BSA = 𝑙𝑏 𝑋 𝑖𝑛

3131 =

𝑘𝑔 𝑋 𝑐𝑚

3600

Calculating a child's dose using an adult dose

Child's dosage = 𝐶𝑕𝑖𝑙𝑑 ′ 𝑠 𝐵𝑆𝐴

1.7 𝑚2 𝑋 𝑎𝑑𝑢𝑙𝑡 𝑑𝑜𝑠𝑎𝑔𝑒

Calculations of intravenous drips

Flow rate ( mL / hr. ) :

Flow rate = 𝑡𝑜𝑡𝑎𝑙 𝑚𝐿 𝑜𝑟𝑑𝑒𝑟𝑒𝑑

𝑡𝑜𝑡𝑎𝑙 𝑕𝑟 . 𝑜𝑟𝑑𝑒𝑟𝑒𝑑

IVI ( Intravenous مللٌلٌتر500فمثال ، ما هو معدل التدفق المطلوب لمرٌض ٌتناول

infusion ) و ٌقرب ألقرب رقم صحٌح . ساعة / مللٌلٌتر 41.66 ساعة ؟؟ سٌكون 12 لمدة

.42فٌكون

Drip rate ( gtt / min. ) :

Drip rate = 𝑡𝑜𝑡𝑎𝑙 𝑚𝐿 𝑜𝑟𝑑𝑒𝑟𝑒𝑑

𝑡𝑜𝑡𝑎𝑙 𝑚𝑖𝑛 . 𝑜𝑟𝑑𝑒𝑟𝑒𝑑 𝑋 𝑑𝑟𝑜𝑝 𝑓𝑎𝑐𝑡𝑜𝑟 ( gtt / mL )

" Drop factor : is the number of drops which make up every millilitre of

fluid delivered " 20: و هو رقم ثابت ٌعطى مع جهاز منظم معدل التدفق و غالبا ما ٌكون

.مللٌلٌتر مع بعض حاالت االطفال / نقطة60مللٌلٌتر و أحٌانا / نقطة15مللٌلٌتر أو /نقطة

% 5 مللٌلٌتر من محلول دكستروز 500ما هو معدل التنقٌط لكل دقٌقة لمرٌض ٌتناول : مثال

مللٌلٌتر ؟ فاالجابة / نقطة 20 ساعة ؟ مع العلم بأن معامل التنقٌط هو 12ورٌدٌا على مدار

.(بعد تقرٌب الرقم ألقرب رقم صحٌح )دقٌقة / نقطة 14= دقٌقة / نقطة13.89ستكون

.الناتج البد و أن ٌكون رقم صحٌح أو ٌتم تقرٌبه الى أقرب رقم صحٌح : ملحوظة


Converting between oC ( Celsius ) &

oF ( Fahrenheit )

oF = 1.8 (oC ) + 32

oC = oF−32

1.8

l ( lower case L و لٌس L ٌكن بحرف Literفً حالة كتابة اختصار وحدة اللتر : ملحوظة

كاملة microgramكما ٌفضل كتابة . عند القراءة " 1" و رقم " l" نظرا للشبه بٌن حرف (

) m اذ قد تتم قراءته خطأ كـ µللتعبٌر عنها بدال من استخدام الرمز الالتٌنً الخاص بها و هو

=milli ًملل ).

Dosage calculations

For tablet dosage form :

Number of tablets = 𝑎𝑚𝑜𝑢𝑛𝑡 𝑝𝑟𝑒𝑠𝑐𝑟𝑖𝑏𝑒𝑑

𝑎𝑚𝑜𝑢𝑛𝑡 𝑖𝑛 𝑒𝑎𝑐 𝑕 𝑡𝑎𝑏𝑙𝑒𝑡

ملجم ، 40 ملجم و األقراص المتاحة هً 120فلو وصف لمرٌض عقار فٌرابامٌل و بجرعة

.اذا عدد األقراص سٌكون ثالثة

For liquid dosage form :

Volume to be given = 𝑎𝑚𝑜𝑢𝑛𝑡 𝑝𝑟𝑒𝑠𝑐𝑟𝑖𝑏𝑒𝑑 𝑋 𝑢𝑛𝑖𝑡 𝑣𝑜𝑙𝑢𝑚𝑒

𝑎𝑚𝑜𝑢𝑛𝑡 𝑝𝑒𝑟 𝑢𝑛𝑖𝑡

25 ) مللجم من عقار تركٌزه 75العطاء مرٌض (مللٌلٌتر )فمثال ، ما هو الحجم المطلوب

مللٌلٌتر3 بالتأكٌد ؟ (مللً /ملجم


Body mass index ( BMI )

عادة ما ٌستخدم لقٌاس معدل السمنة


Drug Timing

Because food can interact with drugs in different ways, perhaps making

the drugs more or less effective, it can be very important to take the

drugs as recommended - before, after or with food.

Always follow the instructions on drugs labels, and if in doubt, talk to a

doctor or pharmacist.

Taking Drugs Before Food

Some drugs need to be absorbed quickly to have an effect, such as

nitrates in angina, drugs to help sleep (hypnotics), drugs to reduce

agitation (sedatives), and painkillers (analgesics). As food can slow the

absorption of these drugs , they need to be taken on an empty stomach.

Taking Drugs With or After Food

Some foods can delay the emptying of the stomach into the small

intestine, where most drugs and nutrients are absorbed. This means that

the stomach contents, including the drug, are exposed to stomach acid

for longer, which can have different effects on different drugs.

The acid in the stomach breaks down some drugs, so delayed emptying

will mean that more of the drug is broken down, and less of the drug is

available, so it will be less effective. The acid in the stomach also

changes some drugs, making them more soluble and so more easily

absorbed. This means that the drug will be more effective, but could

potentially also cause more side effects.

NSAIDs (non-steroidal anti-inflammatory drugs – used in pain and

inflammation), diuretics (used in high blood pressure), some antibiotics,

and corticosteroids (used in inflammation and allergy) can cause

stomach upsets. Taking these drugs, such as ibuprofen, with food (or

milk) can reduce the irritation to the stomach lining.

According to a study carried out in the USA in 2007, taking lapatinib (a

drug used in the treatment of breast cancer) with food, especially fatty


food , could reduce the side effect of diarrhea and lower the dose

needed, which may potentially save money on treatment. According to

the researchers, following up the meal and tablets with a glass of

grapefruit juice (which changes the way the body breaks down the drug)

could make one tablet have the same effect as five tablets taken on an

empty stomach. Patients should only change their pattern of taking

drugs after discussion with a doctor or pharmacist.

Some drugs have to be taken during or after meals to be effective – for

example, obesity drugs is designed to block the absorption of some of

the fat in food as a treatment for obesity. However, if it is taken with a

high fat meal this can cause unpleasant side effects.

Taking the right number of doses of the drug at the right times (known

as ‘adherence’), is very important for the effectiveness of treatment.

Taking drugs with or after meals can help people establish a routine and

remember their treatments. Some people take drugs at bedtime or

when they first get up for a similar reason.

Drug Dose Calculations & Timing

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