Term
Pharmaceutical Calculations
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Definition
- Percentage calculations
- Ratio strengths
- Parts per million
- Alligation alternate
- Alligation medial
- Equivalents, Osmolarity, Normality
- Tonicity
- Electrolytes / energy calculations
- Dry powder reconstitutions
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Term
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Definition
- Most calculations in pharmacy can be expressed as ratios
- Ratios and fractions and can be manipulated by the same rules
- In a ratio, the quantity of one is related to another by a division operation
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Term
Percentage Calculations
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Definition
- Three types of percentage calculations in pharmacy
- Weight/Volume (W/V)
- Grams in 100 mL of solution
- Example: 10% KCl
- Weight/Weight (W/W)
- Grams in 100 grams of solution
- Example: Concentrated HCl
- Volume/Volume (V/V)
- Milliliters in 100 mL of solution
- Example: D5 in 10% ethanol
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Term
Examples of W/V Solutions
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Definition
- Dextrose Solutions
- e.g., 5% Dextrose = 5 gm Dextrose/100 mL
- Sodium Chloride Solutions
- e.g., 0.9% NaCl = 0.9 gm NaCl/100 mL
- Amino Acid Solutions
- Local anesthetics
- Iodine Solutions
- Potassium Chloride Oral Solutions
- Many drugs are mass (weight) / volume
- e.g., gent 40 mg/mL → “gentamicin 4% solution”
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Term
Examples of W/V Solutions
Contd
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Definition
- 5% Dextrose contains 5 gm/100 mL
- 5 gm/100 mL = 5,000 mg/100 mL which equals 50 mg/mL
- 0.75% Bupivacaine is 0.75 gm/100 mL
- 750 mg/100 mL = 7.5 mg/mL
- 1/8% Lidocaine is 0.125 gm/100 mL
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Term
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Definition
- v/v → w/v ← w/w
- Use density to convert w/v and v/v
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Term
Conversion of V/V or W/W
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Definition
- Sometimes formulations are in v/v, but may be dosed in mg
- In Methanol OD, EtOH antidote given:
- Loading Dose (LD): admin 600 mg/kg
- Maint. Dose (MD) 100mg/kg/hour EtOH
- Commercial product: 10% EtOH in D5W
- 10% = v/v, not w/v
- If not careful, could initiate sub-therapeutic patient therapy, depending on severity of overdose, miscalculation could lead to patient death
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Term
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Definition
- No units, reference standard
- Ratio of;
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Term
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Definition
- PP1= parts per 1
- Percent = parts per 100
- PPT = parts per thousand
- PPM = parts per million
- PPB = parts per billion
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Term
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Definition
- Epinephrine comes as a 1:1000 soln
- 1 gram/1000 mL = 1000mg/1000 mL
- 1000mg/1000mL = 1 mg/mL = ____ %
- Benzalkonium Chloride comes as a 1:750 solution
- 1 gram in 750 mL of solution
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Term
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Definition
- To calculate parts per _____ , you need to know how to calculate how much of a single ion.
- • Example: What is the percent (parts per 100) of Ca2+ in 80 grams of CaCO3?
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Term
Parts Per_____
(Its a Ratio)
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Definition
- 5% w/v = 5:100 (if reduced = 1:20)
- 1:1000 (parts per thousand)
- 1 gm in 1000 mL of solution (w/v)
- 1 mL in 1000 mL of solution (v/v)
- 1 gm in 1000 gm of mixture (w/w)
- (don’t get confused - it is % with a different denominator – so its called parts per _____ .)
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Term
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Definition
- Nearly all pharmaceutical calculations utilize manipulation of ratios and dimensional analysis
- Most formulations utilize a percentage calculation
- Easy to make an error if not careful with units and decimals
- Next time: alligation, electrolytes, osmolarity, normality
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