- The amount of a drug in its manufactured or prescribed form is always stated numerically - that is, with numbers
- In pharmacy we use two different number systems: Arabic (such as 1, 1/2, 0.5, or 50%) and Roman (such as I, V, X)
Fractions
- Fractions have numerators and denominators; the denominator of a fraction cannot be zero
- Reciprocals are two different fractions that equal 1 when multiplied together
- The least common denominator is needed when adding or subtracting fractions
Decimal Numbers
- Decimal numbers are another way to express fractions
- Calculations with decimal numbers can be less challenging than fractions with numerators and denominators
Significant Figures
- When working with measured amounts, significant figures provide us with information about the sensitivity of equipment used
Measurement
- Common systems of measurement in pharmacy include the metric, English, apothecary, and avoirdupois systems
- The metric system is the primary system used in pharmacy
Equations and Variables
- Equations are used to calculate unknown amounts that are needed to fill prescriptions or calculate dosages
- An equation is a mathematical statement in which two terms are equal
Alligation
- Alligation is a way to solve problems associated with mixing two different strengths of the same ingredient to make a strength that is in between the two starting preparations
- Once the alligation method is mastered, it becomes an easy and quick way to perform difficult calculations that involve mixing different strengths of the same ingredient
Powder Volume
- Some medications are provided to the pharmacy in powder form but are constituted by the pharmacy so they are dispensed in liquid form
- The final volume of the constituted liquid is equal to the volume of the diluent plus the powder volume of the medication
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