Calculations II: Compounding Flashcards
What are percents and how is it expressed?
A percent is the number of parts in 100. Percents are often often written as decimals or fractions.
What is percent weight-in-volume (%w/v)?
Percent weight-in-volume (%w/v) is expressed as g/100 mL (a solid mixed into a liquid) and applies to common IV fluids
What is percent volume-in-volume (%v/v)?
Percent volume-in-volume (%v/v) is expressed as mL/100 mL (a liquid mixed into a liquid)
What is percent weight-in-weight (% w/w)?
Percent weight-in-weight (% w/w) is expressed as g/100 g (a solid mixed into a solid)
What is the percentage strength of normal saline?
0.9% (w/v) NaCl in water
What is the percentage strength of 1/2NS?
0.45% (w/v) NaCl in water
What is the percentage strength of 1/4NS?
0.225% (w/v) NaCl in water
What is the percentage strength of D5W?
5% (w/v) dextrose in water
What is the percentage strength of D20W?
20% (w/v) dextrose in water
What is the percentage strength of D5NS?
5% dextrose and 0.9% NaCl in water
What is the percentage strength of D51/2NS?
5% dextrose and 0.45% NaCl in water
What is ratio strength and how is it expressed?
Ratio strength is another way of presenting a percentage strength. It is denoted as one unit of solute contained in the total amount of the solution or mixture
How do you convert from ratio strength to percentage strength?
% strength = 100/ratio strength
How do you convert from percentage strength to ratio strength?
Ratio strength = 100/% strength
What are parts per million (PPM) and parts per billion (PPB) used to express?
Parts per million (PPM) and parts per billion (PPB) are used to express the strength of very dilute solutions
What is the definitions of parts per million and parts per billion?
They are defined as the number of parts of the drug per 1 million (or 1 billion) parts of the whole
*The same designations are used as for percentage strength (%w/w, %w/v and %v/v)
What is the shortcut for converting PPM to percentage strength?
Move the decimal left 4 places
What is the shortcut for converting percentage strength to PPM?
Move the decimal right 4 places
What is specific gravity?
Specific gravity (SG) is the ratio of density of a substance to the density of water
What is the specific gravity of water?
Water has a specific gravity of 1 so 1 g of water = 1 mL of water
What does it mean when SG < 1?
Substances with a SG < 1 are lighter than water
What does it mean when SG > 1?
Substances with SG > 1 are heavier than water
What is the formula to calculate specific gravity?
SG = weight of substance (g)/weight of equal volume of water (g)
SG = g/mL
When would you use the Q1C1 formula?
This formula can be used to change the strength or quantity. Q1C1 is used when the problem deals with two concentrations
*The units on each side must match
What is the Q1C1 formula?
Q1 x C1 = Q2 x C2
- Q1 = old quantity
- C1 = old concentration
- Q2 = new quantity
- C2 = new concentration
When would concentration be 100%?
When a prescription calls for an ingredient that is pure
Why is the concentration of a diluent 0%?
A diluent does not contain any drug so the concentration of the diluent is 0%
What is alligation and when is it used?
Alligation is used to obtain a new strength (percentage) that is between two strengths the pharmacist has in stock. It is used when the problem deals with three concentrations
How do you set up an alligation?
1) High goes high: write the higher concentration at the top left
2) Low goes low: write the lower concentration on the lower left
3) Write the desired concentration in the middle
4) Subtract diagonally along the X lines to obtain the number of parts. Write the absolute number (no negative sign) on the right side of the X
5) Label horizontally along the dashed lines; the starting concentrations are carried across
6) For some problems, it will be necessary to add up the total number of parts
What is directly proportional to osmotic pressure?
The total number of particles in a given solution is directly proportional to its osmotic pressure
*The particles are usually measured in milliosmoles
What is osmolarity?
Osmolarity is the measure of total number of particles (or solutes) per liter of solution, defined as osmoles/liter (Osmol/L) or, more commonly as milliosmoles/liter (mOsmol/L)
What does it mean when a solute is ionic or non-ionic?
Solutes can be either ionic (which dissociates into two solutes in solution) or non-ionic (which do not dissociate)
When is osmolality used?
Since the volume of water changes according to temperature, the term osmolality is used in clinical practice because it is independent of temperature
What is the relationship between osmolarity and osmolality?
When solute concentrations are very low, osmolarity and osmolality are similar
How do milliosmole calculations differ from osmolarity calculations?
Milliosmole calculation problems differ from osmolarity calculation problems in that osmolarity will always need to be normalized to a volume of 1 liter
What are examples of compounds that have one dissociation particle?
Dextrose, Mannitol
What are examples of compounds that have 2 dissociation particles?
Potassium chloride, Sodium chloride, Sodium acetate, Magnesium sulfate
What is an example of a compound with 3 dissociate particles?
Calcium chloride
What is an example of a compound that has 4 dissociation particles?
Sodium citrate
What is the osmolality of blood?
~300 mOsmol/kg
What is necessary when solutions are prepared?
When solutions are prepared, they need to match the tonicity of the body fluid as closely as possible
What happens when osmolality is higher in one cellular compartment?
If the osmolality is higher in one cellular compartment, it will cause water to move from the lower to the higher concentration of solutes
What are the adverse effects that can occur with a PN solution with a higher osmolality than blood?
If a PN solution is injected with a higher osmolality than blood, fluid will flow into the vein, resulting in edema, inflammation, phlebitis and possible thrombosis
What formulations is isotonicity desired?
Isotonicity is desired when preparing eye drops and nasal solutions
What is dissociation factor?
The dissociation factor is related to number of particles in solution and symbolized by the letter i
What is the dissociation factor of non-ionic compounds?
Non-ionic compounds do not dissociate and will have a dissociation factor of 1
What is the osmotic pressure of body fluids?
Body fluids are isotonic, having an osmotic pressure equivalent to 0.9% sodium chloride
When preparing a medication, how do you avoid making the prescription hypertonic?
When making a medication to place into a body fluid, the drug provides solutes to the solvent and needs to be accounted for in the prescription in order to avoid making the prescription hypertonic
What is the sodium chloride equivalent or E value?
The relationship between the amount of drug that produces a particular osmolarity and the amount of sodium chloride that produces the same osmolarity is called the sodium chloride equivalent or E value
What is the formula of calculating the E value of a compound?
E = [(58.5)(i)]/[(MW of drug)(1.8)]
What does the E value take into account?
The E value formula takes into account the molecular weight of NaCl (58.5) and the dissociation factor of 1.8 since normal saline is around 80% ionized, adding 0.8 for each additional ion beyond 1 into which the drug dissociates
*The compound being prepared is compared to NaCl because NaCl is the major determinant of the isotonicity of body fluid
What are the steps to doing isotonicity problems once the E.value is determined?
1) Calculate the total amount of NaCl needed to make the final product/prescription isotonic by multiplying 0.9% NS by the desired volume of the prescription
2) Calculate the amount of NaCl represented by the drug. To do this, multiply the total drug amount (in milligrams or grams) by the E value
3) Subtract step 2 from step 1 to determine the total amount of NaCl needed to prepare an isotonic prescription
What is the dissociation factor of a compound that has 1 dissociated ion?
1
What is the dissociation factor of a compound that has 2 dissociated ions?
1.8
What is the dissociation factor of a compound that has 3 dissociated ions?
2.6
What is the dissociation factor of a compound that has 4 dissociated ions?
3.4
What is the dissociation factor of a compound that has 5 dissociated ions?
4.2
What is a mole (mol)?
A mole (mol) is the molecular weight of a substance in grams or g/mole
What is a millimole (mmol)?
A millimole (mmol) is 1/1000 of the molecular weight in grams or 1/1000 of a mole
What is the relationship between milliequivalent and millimoles for monovalent species?
For monovalent species, the numeric value of the milliequivalent and millimole are identical
What is the formula to calculate for mols?
mols = g/MW
What is the formula to calculate mmols?
mmols = mg/MW
What is milliosmoles?
Milliosmoles refers to the number of particles in a solution
What are millimoles?
Millimoles refers to the molecular weight (MW)
What are milliequivalents?
Milliequivalents (mEq) represent the amount, in milligrams (mg) of a solute equal to 1/1000 of its gram equivalent weight, taking into account the valence of the ions. It refers to the chemical activity of an electrolyte and is related to the total number of ionic charges in solution and considers the valence (charge) of each ion
How do you count the valence?
To count the valence, divide the compound into its positive and negative components, and then count the number of either the positive or the negative charges. For a given compound, the milliequivalents of cations equals that of anions
What are some examples that have a valence of 1?
Ammonium chloride, potassium chloride, potassium gluconate, sodium acetate, sodium bicarbonate, sodium chloride
What are some examples of compounds that have a valence of 2?
Calcium carbonate, calcium chloride, ferrous sulfate, lithium carbonate, magnesium sulfate
What is the formula for milliequivalents?
mEq = (mg x valence)/MW = mmols x valence
