Dr.N Damodharan Professor and Head Department of ... · PDF fileEquivalent Values. Percent....
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Transcript of Dr.N Damodharan Professor and Head Department of ... · PDF fileEquivalent Values. Percent....
Proportions in the Pharmacy
• Proportions are frequently used to calculate drug doses in the pharmacy.
• Use the ratio-proportion method any time one ratio is complete and the other is missing a component.
Terminology
a conversion method based on comparing a complete ratio to a ratio with a missing component
ratio-proportion method
Rules for Ratio-Proportion Method
• Three of the four amounts must be known.
• The numerators must have the same unit of measure.
• The denominators must have the same unit of measure.
Percents
• Percent means “per 100” or hundredths.• Represented by symbol %
30% = 30 parts in total of 100 parts,
30:100, 0.30, or10030
Terminology
the number of parts per 100; can be written as a fraction, a decimal, or a ratio
percent
Percents in the Pharmacy
• Multiply the first number in the ratio (the solute) while keeping the second number unchanged, you increase the strength.
• Divide the first number in the ration while keeping the second number unchanged, you decrease the strength.
Converting a Ratio to a Percent
1. Designate the first number of the ratio as the numerator and the second number as the denominator.
2. Multiply the fraction by 100%, and simply as needed.
COMMON CALCULATIONS IN THE PHARMACY
• Converting Quantities between the Metric and Common Measure Systems
• Calculations of Doses• Preparation of Solutions
COMMON CALCULATIONS IN THE PHARMACY
• Converting Quantities between the Metric and Common Measure Systems
Example 4 How many milliliters are there in 1 gal, 12 fl oz?
According to the values in Table 5.7, 3840 mL are found in 1 gal. Because 1 fl oz contains 30 mL, you can use the ratio-proportion method to calculate the amount of milliliters in 12 fl oz as follows:
Example 5 How many hypodermic syringes can be filled with the 3 L of solution?
Determine the number of syringes by using the ratio-proportion method:
Example 6 If the dose is 2 tsp, how many doses will there be in the final preparation?
Using these converted measurements, the solution can be determined one of two ways.
Solution 1: Using the ratio proportion method and the metric system,
Example 7How many grains of acetaminophenshould be used in a Rx for 400 mg acetaminophen?
Solve this problem by using the ratio-proportion method. The unknown number of grains and the requested number of milligrams go on the left side, and the ratio of 1 gr 65 mg goes on the right side, per Table 5.5.
Example 8A physician wants a patient to be given 0.8 mg of nitroglycerin. On hand are tablets containing nitroglycerin 1/150 gr. How many tablets should the patient be given?Begin solving this problem by determining the number of grains in a dose by setting up a proportion and solving for the unknown.
Example 14 How much diluent will you need if the original product is in a 1 mL vial and you dilute the entire vial?
Example 15Prepare 250 mL of dextrose 7.5% weight in volume (w/v) using dextrose 5% (D5W) w/v and dextrose 50% (D50W) w/v. How many milliliters of each will be needed?
Example 15 How many milliliters of each will be needed?Step 1. Set up a box arrangement and at the
upper-left corner, write the percent of the highest concentration (50%) as a whole number.
Example 15 How many milliliters of each will be needed?
Step 2. Subtract the center number from the upper-left number (i.e., the smaller from the larger) and put it at the lower-right corner. Now subtract the lower-left number from the center number (i.e., the smaller from the larger), and put it at the upper-right corner.