Math practice Flashcards
conversions metric system
1 oz- 30 g 1 lb - 454 g 2.2 lb- 1 kg 1 tsp- 5 mL 1T - 15 mL 1 fl oz- 30 mL 1 cup (8 fl oz) - 240 mL 1 pint (16 fl oz) 480 mL 1 quart (32 fl oz)- 960 mL
Dosage calculation:
Ex: A patient needs to take a 250 mg dose of a medication, and the pharmacy stocks 125 mg/5 mL. How much volume should be dispensed?
Start with what you are looking for and make this your x. We are looking for volume, which in this case equals mL. Now put this unknown over your dose—we are trying to find the volume that goes with the dose that was ordered.
x mL/ 250 mg= 5ml / 125 mg
Day Supply:
Take 1 tab PO TID dispense #30
Step 1. Determine how much in one day: 1 tab × 3 = 3 tabs
Step 2. Divide the quantity dispensed by the amount taken in one day: 30 ÷ 3 = 10
This prescription is a 10-day supply.
DS= Quantity/ (dose * Frequency)
Percent Error:
You are to dispense 500 mg of a powder. The first measurement taken is 500 mg, but when a more accurate balance is used, you determine the measurement to be 505 mg. What is the percentage of error?
Step 1. Find the amount of error = 505 – 500 = 5
Step 2. Divide this by the exact value (500) = 5 ÷ 500 = 0.01
Step 3. Convert to percent by multiplying by 100 = 0.01 × 100 = 1% error
Units: insulin, heparin, penicillin
Example: If a patient requires 35 units of insulin, how many mL will be injected?
Insulin is always 100 units in 1 mL and generally comes in a 10 mL vial.
x ml/ 35 units= 1 ml/ 100 units
result: 0.35 ml
Milliequivalents (mEq)
Example: If a patient is to get 25 mEq of potassium, and the pharmacy stocks a 40 mEq/mL vial, how much should be injected into the patient?
Units used to measure electrolytes—the strength of an ion in a medication Examples of medications measured in milliequivalents: • potassium chloride • sodium • phosphate x ml/ 25 mEq= 1ml/ 40 mEq
Concentrations and dilutions
Example: You are making 1 L of a 0.7% solution. You have a stock of 15% solution to use. How much stock will you need to make this product?
A concentrate is a drug that must be diluted prior to administration. A diluent is an inactive substance added to the concentrate to lower the concentration of the final solution.
To calculate, use a simple formula: C1V1 = C2V2 C1 = the concentration of the stock
V1 = the volume of the stock used
C2 = the concentration of the final product
V2 = the volume of the final product
0.7)(1,000) ÷ 15 = 46.7 mL of stock
To determine the amount of diluent you will need, simply subtract this value from the final volume:
1,000 mL – 46.7 mL = 953.3 mL of diluent
Temperature Conversions
When converting from Celsius temperature to Fahrenheit, use the following formula:
°F = (1.8 × °C) + 32
When converting from Fahrenheit temperature to Celsius, use the fol- lowing formula:
°C = (°F – 32)/ 1.8
Percent strength
Example: A 5% solution
The concentration of a drug or active ingredient (solute) dissolved in a vehicle (solvent) expressed as a fraction, ratio, or percentage.
Example: A 5% solution can be written as 5/100, 5:100 or 0.05.
Alligations
Example: Make 200 mL of a 5% solution using 2.5% and 10% stock solutions. How much of each will you need?
x quantity of y% out of a% and A% concentrations A.....y-a "parts of A%" ....y..... a.....A-y "parts of a%" (y-a) + (A-y)= T total parts 1. (y-a)/T= k1...... x*k1 ml of A% 2. x ml - xk1= ml of a%
Weight/weight:
How much active ingredient is in a 45 g tube of 2.5% cream?
X g / 45g = 2.5 g/ 100g
(2.5 * 45 g) : 100= 1.125 g of drug in a 45 g tube
Weight/volume (w/v)
A 2.5% solution has 2.5 g of drug in 100 mL of product.
Example: How many grams of active ingredient are in 500 mL of a 23% solution?
23% w/v = 23 g/100 mL
(500)(23) ÷ 100 = 115 g of drug in 500 mL of 23% w/v solution
volume/volume (v/v)
The number of milliliters of a drug in 100 mL of final product.
Example: A 2.5% solution has 2.5 mL of drug in 100 mL of solution.
We can use this ratio to determine how much active ingredient would be in a given quantity.
Example: How many milliliters of IPA are in 250 mL of a 70% solution?
Remember: 70% v/v = 70 mL/100 mL
(250)(70) ÷ 100 = 175 mL of IPA in 250 mL of 70% v/v solution
IV Flow rates
Example: If a 1,500 mL IV is infused over 5 hours, what is the infusion rate?
1500ml/ 5 h= 300 ml/ hr
Example: If a 1,500 mL IV is infused at a rate of 300 mL/hr, what is the time of infusion?
1500ml : 300 ml/ hr= 5 hr
Volume Inf time.... inf rate
IV drip rates
Example: If a patient has a 500 mL order for 4 hours and a drop factor of 20 gtt/mL, what is the drip rate?
to calculate gtt/min:
(Total volume) × (drop factor) __________________________
Total minutes
Example: If a patient has a 500 mL order for 4 hours and a drop factor of 20 gtt/mL, what is the drip rate?
First, convert hours to minutes: 4 hours × 60 minutes = 240 minutes. (500)(20) ÷ 240 min = 4 gtt/min
