Dimensional Analysis
What is the overall name of the kind of units we need to use for Pharmacy Calculations?
International System of Units (SI)
The Metric System
What is the fundamental unit of a prescription?
Dose
A patient requires 250 mL D5W.
Stock solution is D70.
What kind of problem is this, and what is my process?
This is a v/v dilution.
I need to set up 70% as my C1, 5% as my C2, and 250 mL as my V2.
Rx:
Day 1 = 2 before breakfast, 1 after lunch and dinner, and 2 before bedtime
Day 2 = 2 before breakfast, 1 after lunch and dinner, and 1 before bedtime
Day 3 = 1 before breakfast, 1 after lunch and dinner, and 1 before bedtime
Day 4 = 1 before breakfast, 1 after lunch, and 1 before bedtime
Day 5 = 1 before breakfast, 1 before bedtime
Day 6 = 1 before breakfast
Find the total
Total = 21
Rx = Amoxicillin 250 mg capsules ii po TID x 10 D
What amount of medication is this patient getting per day?
1500 mg
Grams
Why do we need to know how many doses a patient will take in a day?
Therapeutic dosing happens on a schedule, and that schedule typically follows the day-night cycle, up to 24 hours.
What does (C1)(Q1) = (C2)(Q2) mean?
(C1)(Q1) = (C2)(Q2) means:
Concentration 1 multiplied by Quantity 1 equals Concentration 2 multiplied by Quantity 2.
If a 2 L bag was run at 125 mL / hr, when would it stop, if it was started at 10:00 a.m.?
2:00 a.m. (the next day)
Medication = Nystatin 100,000 units / mL
Rx = 50,000 units po BID
Disp. 60 mL
How much Nystatin is dispensed?
6,000,000 units
What is the standard dimension for concentration of liquids?
milliliters (mL)
Why do we need to know the duration of a prescription?
1) To be able to identify the quantity to dispense
2) To know how long a therapy needs to last before a new script / a refill is necessary
What is another name for the 1 and the 2 signifiers?
1 and 2 mean Initial and Final.
If you need to dilute a powdered drug, but you are not making the final product into a solution, give some examples of what could be used:
1) Filler powder
2) Ointment base, Cream base, paste base
3) Turn it into a compressed tablet with excipients
How many 50 mg doses are available?
192
grams-in-milliliters
iii po QOD x 30 D
What is the quantity dispensed?
Take 3 by mouth every other day for 30 days
QD = 45
Medication = 250 mg / 15 mL
Rx = 8 oz po BID x 10 D
If asked, "How strong is the dose taken each day?", what dimension would you answer be in?
Dimension = mg
What are two ways to dilute an active ingredient?
1) Mix it with a less concentration of the same ingredient
2) Mix it with an inert / base solvent
Rx = 30mg / kg / day divided 12qh
What is the daily dose for a patient weighing 100 lbs.?
1364 mg
When you dilute something, what dimension gets smaller, and what dimension gets larger?
Concentration gets smaller; volume gets bigger.
ss po BID
Disp. = 90
What is my days' supply?
Take 1/2 po mouth twice a day
DS = 90 Days
Medication = 50 mcg tablets
Rx = 150 mcg q4-6h PRN x 30 D
If asked, how many tablets does this patient take in a day, what information provided above is NOT needed?
Answer = duration (30 Days)
Medication = 250 mg per 100 mL
Rx = 500 mg over 200 minutes
What is the drop factor you would use?
Which terms can be used if a medication is not measured in actual weight of active ingredient?
Milliequivalents or (international) units