Transcript Calculation of Doses I Dr. Osama AA Ahmed

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: the schedule of dosing (4 times per day for 10
days)
•
Dr. Osama A. A. Ahmed
number of doses  total quantity
Size of dose
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Dose Definitions
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Usual adult dose: the amount that ordinarily produces the medicinal effect intended
in the adult patient
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Usual pediatric dose: : the amount that ordinarily produces the medicinal effect
intended in the infant or child patient
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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.
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Average serum conc. (mg/ml)
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MTC
MEC
Time after drug administration (hours)
Minimum toxic concentration:
The base level of blood serum concentration that produces dose-related toxic effects.
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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)
ounce
Metric system
1 teaspoonful (tsp)
1 tablespoonful (tbsp)
1/6 fluidounce
1/2 fluidounce
5 ml
15 ml
Dr. Osama A. A. Ahmed
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Dose Measurement
Household measures
Signa
Label
dose
f
One teaspoonful
5 ml
One dessertspoonful
10 ml
One tablespoonful
15 ml
f
One coffee cupful
30
m
One drop
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• 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).
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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
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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
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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: 1 year through 5 years
• Late childhood: 6 years through 12 years
• Adolescence: 13 years through 17 years of age
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Calculation of doses
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Patient Parameters
According to age
Child and infant doses
Young’s rule
 X adult dose
Dose for Child   Age of child  years 
age  years   12

• Cowling’s rule
Dose for Child   Age at next birthday  years   X adult dose
24

• Fried’s rule for infants
 X adult dose
Dose for Infant   Age months
150

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Calculation of doses
• Patient Parameters
• According to body weight
• Clark’s rule
 X adult dose
Child dose  weight lb 
150

• According to body surface area (BSA)
 
 BSA of the child m 2

Child dose  
2  X adult dose
1.73 m 

 
Child dose  BSA of the child m2 X dose per m2
• To determine patient’s BSA, use standard Nomogram or this equation
Patient ' s height cm Patient ' s weight kg
Patient ' s BSA m 
3600
 
2
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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
 X adult dose
Dose for Child   Age of child  years 
age  years   12

•
= (8/8+12)X 15 = 6 mg
• Cowling’s rule
Dose for Child   Age at next birthday  years   X adult dose
24

•
Dr. Osama A. A. Ahmed
= (9/24)X 15 = 5.625
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