Calculation of Doses I

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Calculation of Doses I
Dr. Osama A. A. Ahmed
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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)

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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 drugs
• desired effects in a patient.
• 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 childs 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 f f ss
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Dose Measurement

• Household measures
• Calibrated droppers
• US Pharmacopeia, official medicinal dropper held
  vertically delivers approximately 20 drops water
  per millilitre.
• A drop (abbreviated gtt) doesnt represent a
  definite quantity (few liquids have the same
  surface and flow characteristics as water).

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


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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 childs 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

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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

• Patient Parameters
• According to age
• Child and infant doses
• Youngs rule
• Cowlings rule
• Frieds rule for infants

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Calculation of doses

• Patient Parameters
• According to body weight
• Clarks rule
• According to body surface area (BSA)
• To determine patients BSA, use standard Nomogram
  or this equation

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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?
• Youngs rule
• (8/812)X 15 6 mg
• Cowlings rule
• (9/24)X 15 5.625