Pharmacy calculations
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Pharmacy calculations

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Pharmacy calculations Pharmacy calculations Presentation Transcript

  • Pharmacy Calculations Numbers/Fractions Decimal/Significant Figures Measurements/Equations & Variables Ratio & Proportion Percents & Solutions
  •  
  • Numerals
    • ss
    • I or i
    • V or v
    • X or x
    • L or l
    • C or c
    • D or d
    • M or m
    • ROMAN
    • 0.5 or ½
    • 1 (one)
    • 5
    • 10
    • 50
    • 100
    • 500
    • 1000
    • ARABIC
  • Practice Problems
    • Caps no. xiv
    • Gtts ix
    • Tabs # XLVIII
    • Tabs # xxi
    • Gms xlv
    • ii tsps
    • Positional Notation---
    • Position of the number carries a mathematical significance or value-
    • 14 capsules
    • 9 drops
    • 48 tablets
    • 21 tablets
    • 45 grams
    • 2 teaspoonfuls
    • Second of two letters is:
    • Smaller --- ADD
    • Larger --- SUBTRACT
  • A Fraction……
    • Is a numerical representation indicating there is a part of a whole (3/4,5/8).
    • Represents the division of two numbers.
    • Has a denominator (number below the bar), which tells us how many parts the whole is divided into.
    • Has a numerator (number above the bar), which tells us how many of those parts exist.
    • One way to think of a fraction is as a division that has not been completed.
    • ¼ 0.25 25/100 25%
    • ½ 0.5 50/100 50%
    • ¾ 0.75 75/100 75%
  • Decimal Numbers Power of 10
    • Adding & Subtracting
    • First- put the #’s in a vertical column
    • Aligning decimal points
    • Add starting Right to Left and carry
    • Subtract starting Rt-Lt and borrow
    • 4 + 3.1 + 0.3 + 5.001= ?
    • 4.0
    • 3.1
    • 0.3
    • 5.001 = 12.401
    • Subtract 1.203 from 32.55
    • 32.55
    • - 1.203 = 31.347
  • Decimals cont.
    • Multiplying Decimals
    • First, align numbers on the right
    • Multiply normally & add the products
    • Finally, count the decimal places
    • Multiply 9.683 by 6.1
    • 9.683
    • x 6.1
    • 9683
    • 58098
    • 590663 how many decimals?
    • 59.0663
  • Significant Figures
    • The actual value we can use in our calculations depends on the sensitivity of the measuring device. Last figure to the right is approximation. RULES
      • Digits other than zero are always significant 453.7g
      • Final zeros after a decimal point are always significant 0.100mg=100mcg
      • Zeros between two other significant digits are always significant 101g
      • Zeros used only to show the location of the decimal are never significant 0.123mg 00123.4560
    • Rounding off retains significance of least #
        • 1.65370 x 0.26 = 1.65 x 0.26 = 0.4290 = 0.43
  • Pharmacy Measurement Systems
    • Metric System
      • Liquids (Volume)
        • Liter 1L = 10 dL = 1000mL
        • Milliliter 1mL = 0.001 L
          • Milliliters = cubic centimeters (cc)
      • Solids (Weight)
        • Kilogram 1kg = 1000g
        • Gram 1g (gm) = 0.001kg=1000mG
        • Milligram 1mG= 0.001g=1000mcg
        • Microgram 1 mcg= 0.001mG =0.000001g
      • Length (na)
  • Measurements cont.
    • Avoirdupois System
      • Pound 1 lb=16oz
      • Ounce 1 oz=437.5
      • Grain 1gr=64.8mg
    • Apothecary System (Metric)
      • Gallon 1gal=4qt 3840mL
      • Quart 1qt=2pt 960mL
      • Pint 1pt=16 fl oz 480mL
      • Fluid Ounce 1fl oz=6 fl dr 30mL
      • Fluid dram 60 minims 5 mL
  • Measurements cont.
    • Household units
      • Teaspoon 1 tsp=5mL
      • Tablespoon 1tbsp=3tsp=15mL
        • 2 tbsp = 30ml = 1 fl oz
      • Cup 1cup=8 fl oz
    • Temperature ~~~
      • Centigrade (Celsius) C
      • Fahrenheit, F
        • 9C=5F-160
    • International Units
      • IU
      • Measures the amount of drug in units
      • Penicillin, heparin, insulin, vitamin E
    • Milliequivalents
      • mEq
      • Refer to positively charged ions per liter of salt solution
      • Klor-con 8mEq
  • Conversions
    • Change one unit of measure into another
    • 1pt=473.167mL (473mL) (480mL)
    • 1 fl oz=29.57mL (30mL)
    • 1kg=2.2lb
    • 1g=1000mG
    • 1lb=453.59gm (454g)
    • 1oz=28.35gm (30g)
    • 1gr=64.8mG (65mg)
    • 1g=1000mG
    • 1 fl dr= 5mL
  • Equations & Variables X
    • An equation is a mathematical statement in which two terms are equal.
    • There is often an unknown value that needs to be determined, called a variable, indicated by x.
  • Problem Solving an RX
    • RX: Amoxicillin 250mg tid for 7 days. How many capsules need to be dispensed?
    • (doses needed) x =(caps per dose)(dose/day) (days)
    • x=1x3x7 = 21 capsules of Amoxicillin to fill the Rx.
    • RX: Phenergan w/Cod Liq 120 ml How many Fluid ounces will be dispensed?
    • x fl oz= (total prescribed ml) x (conversion Rate)
    • x fl oz= 120 ml x 1 fl oz
    • 29.57 ml
    • x fl oz = 4 (approx)
  • Ratio and Proportion~
    • A relationship between two quantities : A or A:B
    • B
    • RULES for Solving
    • Three of the four values must be known
    • Numerators must have the same units
    • Denominators must have the same units
    • Two equal ratios form a proportion :
    • A = C or AD=BC
    • B D
    • STEPS for Solving~~
    • Write problem in ratio form
    • Select conversion equation
    • Diagonal multiply & divide
    • OR
    • x=( D esired) x Q uantity~~
    • H ave
  • Critical Thinking ERRORS !
    • RX Prelone 15mG /5mL
    • 15mG po BID
    • ERROR: Order misread 15mL BID
    • Patient received 15 mL instead of 5 mL or 45 mG
    • Potential Outcome: hi dose steroid
    • GI bleed, HA, Seizures, HTN
    • PREVENTION:
    • mG is weight – mL is volume
    • RX ASA 325mg
    • 10gr qd
    • ERROR: Order misread
    • 10 grams
    • Patient received 16 times dose
    • Potential Outcome: GI heartburn,nausea,bleed
    • PREVENTION: order in apothecary, supply in metric,decimal point
    • 10gr (60mg/1gr)=600mg
  • Percents and Solutions
    • Are used to indicate the amount or concentration of something in solution
    • Concentrations are in terms of weight to volume OR volume to volume
    • Wt per Vol (w/v) = grams per 100 milliliters g/100mL
    • Vol per Vol (v/v) =milliliters per 100 millilters ml/ 100mL
    • Wt per Wt (w/w) = grams per 100 grams g/100 g
    Part Whole %
  • Critical Thinking ERRORS !
    • RX Keflex 80mg po QID
    • Supply Keflex 250mg/5ml
    • ERROR Incorrect ratio setup
    • Patient received 9.75 x dose
    • 80mg = 250 mg x=15.6ml
    • 5 ml x ml
    • Potential Outcome :renal/liver
    • Impairment; BUN/liver labs;
    • Family notified & incident report
    • PREVENTION: correct ratio
    • 250mg = 80 mg x=1.6ml
    • 5ml x ml
    • Desired x Q = x
    • Have
    • 80mg x 5ml = x
    • 250mg
    • *check that units cancel
    • *check that number makes sense
  • Practice Pharmacy Problems