Calculation of Doses I

Dr. Osama A. A. Ahmed

Dose Definitions

•

Dose of a drug :

the quantitative amount administered or taken by a patient for the intended medicinal effect •

Single dose:

the amount taken at one time • • • •

Total dose (Daily dose)

: the amount taken during the course of therapy (may be subdivided in divided doses)

Dosage regimen:

days) the schedule of dosing (4 times per day for 10

number of doses



total quantity Size of dose

Dr. Osama A. A. Ahmed 2

•

Dose Definitions

Usual adult dose:

the amount that ordinarily produces the medicinal effect intended in the adult patient •

Usual pediatric dose: :

the amount that ordinarily produces the medicinal effect intended in the infant or child patient • • •

Usual dosage range

: the quantitative range or amounts of the drug that may be prescribed within the guidelines of usual medical practice

Median effective dose:

the amount that produces the desired intensity or effect in 50% of the individuals tested.

•

Minimum effective concentration:

the minimum concentration determined that can be expected to produce the drug’s desired effects in a patient. MTC MEC • •

Minimum toxic concentration:

Time after drug administration (hours) The base level of blood serum concentration that produces dose-related toxic effects.

Dr. Osama A. A. Ahmed 3

Dose Measurement

• Doses are measured and administered by professional and paraprofessional personnel in case of institutional setting.

• adults or child’s parents are generally measures and administers medication in the home setting.

• Household measures Household measure (Abbreviation) 1 teaspoonful (tsp) 1 tablespoonful (tbsp) ounce 1/6 fluidounce 1/2 fluidounce Metric system 5 ml 15 ml f f ss

Dr. Osama A. A. Ahmed 4

Dose Measurement Household measures

Signa

f i f ii f f ss m

Label

One teaspoonful One dessertspoonful One tablespoonful One coffee cupful One drop

dose

5 ml 10 ml 15 ml 30 •

Calibrated droppers

• US Pharmacopeia, official medicinal dropper held vertically delivers approximately 20 drops water per millilitre.

• A drop (abbreviated water).

gtt

) doesn’t represent a definite quantity (few liquids have the same surface and flow characteristics as

Dr. Osama A. A. Ahmed 5

Dose Measurement

•

Case 1

• A physician asks a pharmacist to calculate the dose of a cough syrup so that it may be safely administered dropwise to a child. The cough syrup contains the active ingredient dextromethorphan HBr, 30 mg/15 ml, in a 120- ml bottle. Based on the child’s weight and literature references, the pharmacist determines the dose of dextromethorphan HBr to be 1.5 mg for the child. The medicine dropper to be dispensed with the medication is calibrated by the pharmacist and shown to deliver 20 drops of the cough syrup per 1 ml.

Calculate the dose in drops, for the child. •

Answer

• 30 mg dextromethorphan HBr 15 ml • 1.5 mg dextromethorphan HBr X ml • X = 15 * 1.5/30 = 0.75 ml • Number of drops of cough syrup in 0.75 ml dose • 1 ml 20 drops of cough syrup • 0.75 ml X drops of cough syrup • X = 0.75 * 20/1 = 15 drops of cough syrup

Dr. Osama A. A. Ahmed 6

Calculation of doses

• • •

Patient Parameters Geriatric medicine or geriatrics:

is the field that encompasses the management of illness in the elderly

Pediatrics:

is the branch of medicine that deals with disease in children from birth through adolescence.

• • • • •

Neonate

(newborn): from birth to 1 month, neonate is considered

premature

if born less than 37 weeks‘ gestation

Infant:

1 month to 1 year

Early childhood: Late childhood: Adolescence:

1 year through 5 years 6 years through 12 years 13 years through 17 years of age

Dr. Osama A. A. Ahmed 7

Calculation of doses

•

Patient Parameters

• • •

According to age Child and infant doses Young’s rule

Dose for Child

  

Age of child



years



age



years

  12  

X adult dose

•

Cowling’s rule

Dose for Child

  

Age at next birthday



years

 24  

X adult dose

•

Fried’s rule for infants

Age



Dose for Infant

  

months

 150  

X adult dose Dr. Osama A. A. Ahmed 8

Calculation of doses

• • • •

Patient Parameters According to body weight Clark’s rule

Child dose

  

weight

  150  

X adult dose

According to body surface area (BSA)

Child dose

  

BSA of the child Child dose



BSA of the child

1 .

73

m

2  

X adult dose X dose per m

2 • To determine patient’s BSA, use standard Nomogram or this equation

Patient

'

s BSA



Patient

'

s height

  

Patient

'

s weight

3600

Dr. Osama A. A. Ahmed 9

Calculation of doses

• If the adult dose of phenobarbital is 15 mg, what will be the dose for an 8 year-old child?

• •

Young’s rule

Dose for Child

  

Age of child



years



age



years

  12  

X adult dose

= (8/8+12)X 15 = 6 mg • •

Cowling’s rule

Dose for Child

  

Age at next birthday



years

 24  

X adult dose

= (9/24)X 15 = 5.625

Dr. Osama A. A. Ahmed 10