Calculation of Doses I
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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

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Calculation of Doses I

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Calculation of doses i

Calculation of Doses I

Dr. Osama A. A. Ahmed


Dose definitions

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


Dose definitions1

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.

Minimum toxic concentration:

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

Dose Definitions

MTC

Average serum conc. (mg/ml)

MEC

Time after drug administration (hours)

Dr. Osama A. A. Ahmed


Dose measurement

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

Dr. Osama A. A. Ahmed


Dose measurement1

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

Dr. Osama A. A. Ahmed


Dose measurement2

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

Dr. Osama A. A. Ahmed


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

Calculation of doses

Dr. Osama A. A. Ahmed


Calculation of doses1

Calculation of doses

  • Patient Parameters

  • According to age

  • Child and infant doses

  • Young’s rule

  • Cowling’s rule

  • Fried’s rule for infants

Dr. Osama A. A. Ahmed


Calculation of doses2

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

Calculation of doses

Dr. Osama A. A. Ahmed


Calculation of doses3

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

Calculation of doses

Dr. Osama A. A. Ahmed


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