Calculation of Doses I Dr. Osama A. A. Ahmed. 2 Dose of a drug : the quantitative amount...

Calculation of Doses I

Dr. Osama A. A. Ahmed

Dr. Osama A. A. Ahmed 2

• 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: the schedule of dosing (4 times per day for 10

days)

•

Dose Definitions

doseofSizequantitytotaldosesofnumber


• 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 determinedthat can be expected to produce the drug’sdesired effects in a patient.

• Minimum toxic concentration: • The base level of blood serum concentration that produces dose-related toxic effects.

Dose Definitions

MTC

MEC

Ave

rage

ser

um c

onc.

(g

/ml)

Time after drug administration (hours)


• 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

Dose Measurement

Household measure (Abbreviation)

ounce Metric system

1 teaspoonful (tsp)

1 tablespoonful (tbsp)

1/6 fluidounce

1/2 fluidounce

5 ml

15 ml

f

f ss


Household measures

• Calibrated droppers• US Pharmacopeia, official medicinal dropper held vertically

delivers approximately 20 drops water per millilitre.• A drop (abbreviated gtt) doesn’t represent a definite quantity

(few liquids have the same surface and flow characteristics as water).

Dose Measurement

Signa Label dose

f i One teaspoonful 5 ml

f ii One dessertspoonful 10 ml

f ss One tablespoonful 15 ml

f One coffee cupful 30

m One drop


• 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

Dose Measurement


• 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: 1 year through 5 years

• Late childhood: 6 years through 12 years

• Adolescence: 13 years through 17 years of age

Calculation of doses


• Patient Parameters• According to age• Child and infant doses• Young’s rule

• Cowling’s rule

• Fried’s rule for infants


doseadultXyearsage

yearschildofAgeChildforDose

12

doseadultXyearsbirthdaynextatAgeChildforDose

24

doseadultXmonthsAgeInfantforDose

150


• Patient Parameters• According to body weight• Clark’s rule

• According to body surface area (BSA)

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


doseadultXlbweightdoseChild

150

doseadultXm

mchildtheofBSAdoseChild

2

2

73.1

22 mperdoseXmchildtheofBSAdoseChild

3600

''' 2 kgweightsPatientcmheightsPatient

mBSAsPatient


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

• Young’s rule

• = (8/8+12)X 15 = 6 mg

• Cowling’s rule

• = (9/24)X 15 = 5.625


doseadultXyearsage

yearschildofAgeChildforDose

12

doseadultXyearsbirthdaynextatAgeChildforDose

24

Calculation of Doses I Dr. Osama A. A. Ahmed. 2 Dose of a drug : the quantitative amount...

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