Order Entry and Processing Study Guide for the PTCB Exam
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General Information
Order Entry and Processing questions on the newest version of the PTCB exam take up 22.5% of the test, so, still a little under one-fourth. That percentage has been reduced by just over 1% from the previous exam edition. Be sure you are well versed in the content covered in this study guide.
Vocabulary and Procedures
As a pharmacy technician, it is important to know and understand pharmacy-related verbiage, calculations, and procedures. You must be able to “talk the talk to walk the walk,” as they say. Being competent in these areas will help with effective communication, improve your patient care, and ultimately lead to success in your daily tasks and duties.
Calculations
A pharmacy technician must have a firm understanding of basic pharmacy calculations, regardless of whether their specific daily tasks involve such calculations. Although the pharmacist-on-duty will ultimately double-check that calculations are done correctly, it makes for a more efficient and fluid workflow if the pharmacy technician is proficient and confident in their mathematical skills.
Formulas
An important method to know when performing pharmacy calculations is dimensional analysis. This method uses ratios to calculate a desired quantity or answer. As a formula, think of it like this: To get the desired total quantity (T), you multiply the given quantity (Q) by the conversion factor (CF):
\[T = Q \times CF\]We’ll practice with a simple example, converting inches to centimeters. Below, we’ll provide a fuller list of common conversion factors, but for now we’ll just tell you that one inch is equal to 2.54 centimeters. So, if we need to convert 20 inches to centimeters, we can simply input those numbers into the formula we just learned:
\[20 \times 2.54 = 50.8\]Since we’re working with units of measurement, however, the process is actually a bit longer. We need to include the units in our calculation, like so:
\[20 \text{ in} \times \dfrac{2.54 \text{ cm}}{1 \text{ in}} = 50.8 \text{ cm}\]The inches in that equation get canceled out to leave us with centimeters.
In some problems, you may need two conversion factors. For example, suppose you have a male patient who weighs 141 pounds. His doctor prescribed a medication that has a specific weight-based dosing of five milligrams per kilogram per day. How many milligrams of medication should be prescribed per day?
You need two more conversion factors to come up with an answer. The first is the basic conversion from pounds to kilograms:
\[1\text{ kg} = 2.2\text{ lb}\]Since the dose rate is \(\frac{5 \text {mg}}{1 \text {kg}}\), that will be used as the second conversion factor to convert kilograms of body mass into milligrams of medication:
\[141 \text{ lb} \times \frac{1 \text{ kg}}{2.2 \text{ lb}} \times \dfrac{5 \text{ mg}}{1 \text{ kg}}\]After crossing out like units, we have:
\[\dfrac{141 \times 1 \times 5 \text{ mg}}{2.2 \times 1 } = 320.45 \text{ mg}\]Ratios and Proportions
A ratio is the relative value between two numbers. The fraction \(\frac{1}{2}\) can be read as the ratio \(1 \text{:} 2\), which in turn means “one part for every two parts.” Suppose a mixture has a parts-per ratio of \(1 \text{:} 1 \text{:} 1\). This ratio shows that each ingredient of the mixture has equal parts.
Since ratios are fractions, they follow basic fraction rules. For instance, a fraction of \(\frac{4}{8}\) can be reduced down to \(\frac{2}{4}\) and furthermore to \(\frac{1}{2}\), with all three equaling the ratio \(1 \text{:} 2\). This means that all three fractions are equivalent.
A proportion expresses the equality of two ratios. Proportions can be expressed in a few different ways, including:
- a:b = c:d
- a/b = c/d
- a:b :: c:d
Setting up a proportion helps us find the missing value in the equivalent expressions. For example, if 100 milligrams of morphine concentrate equals five milliliters, then how many milliliters are needed to provide 10 milligrams? To know for sure, set up a simple proportion:
\[\dfrac{100 \text{ mg}}{10 \text{ mg}} = \dfrac{5\text{ mL}}{x}\] \[100 \ x = 50 \text{ mL}\]This can be expressed as:
\[x=\dfrac{50 \text{ mL}}{100}\]That gives us:
\[x = 0.5 \text{ mL}\]So, \(\dfrac{100 \text{ mg}}{5 \text{ mL}}\) is equivalent to \(\dfrac{10 \text{ mg}}{0.5\text{ mL}}\), with both equaling the ratio \(20 \text{:} 1\).
Conversions
As stated in previous sections, it is important to know units of measure and how to convert from one to another. Here is a simple list of different units of measure conversions that should be committed to memory:
| Volume | Weight | Length |
|---|---|---|
| 1 tsp = 5 mL | 1 kg = 2.2 lb | 1 in = 2.54 cm |
| 1 tbsp = 15 mL | 1 gm = 10 dg = 100 cg = 1,000 mg = 1,000,000 mcg |
|
| 1 L = 10 dL = 100 cL = 1,000 mL = 1,000,000 mcL |
1 gr = 64.8 mg | |
| 1 mL = ~20 gtt | 1 lb = 16 oz | |
| 1 gal = 4 qts | 1 lb = ~454 gm | |
| 1 fl oz = 29.6 mL | ||
| 1 qt = 2 pt | ||
| 1 pt = ~473 mL |
Knowing these will help when performing dimensional analysis, when calculating dosing, or when converting from one dosing unit of measure to another.
Note: You should also be familiar with these unit abbreviations, including gtt for drops and mcg for micrograms.
Let’s try an example problem.
Your patient was given a prescription for Eye Drop X, with the directions to use one drop in each eye every four hours for seven days. Eye Drop X is commercially available in the following quantities: 2.5 milligrams, 5 milligrams, 10 milligrams, and 20 milligrams. Which would you dispense to be sufficient for the patient’s course of therapy?
Solution
One drop in each eye every four hours for seven days equals 84 total drops. To convert drops to milligrams, we do a basic conversion:
\[84\text{ gtt} \div 20 = 4.2\text{ mL}\]As such, a five-milliliter bottle is the smallest package size and the best reasonable choice to dispense to sufficiently cover this patient’s seven-day course of therapy.
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