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Chapter 6 Calculation of Oral Medications─Solid and Liquids. Dosage Calculations. D = Desired dose or order H = On hand or have S = Supply. Three Methods of Dosage Calculation. Proportion expressed as two fractions Proportion expressed as two ratios Formula method.
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Dosage Calculations • D = Desired dose or order • H = On hand or have • S = Supply
Three Methods of Dosage Calculation • Proportion expressed as two fractions • Proportion expressed as two ratios • Formula method
Proportion Expressed as Two Fractions • SUPPLY = X HAVE DESIRE
Proportion Expressed as Two Ratios • SUPPLY : HAVE :: X : DESIRE
Formula Method • DESIRE × SUPPLY = X HAVE
Clearing Decimals • When the numerator and denominator in Desire/Have are decimals, add zeros to make the number of decimal places the same • Then drop the decimal points • Operation replaces long division
Important to Remember • Before solving problems, check to be certain the order and supply are in the measure • If not in same measure, must convert one or the other to its equivalent
Question The client is to receive acetaminophen 975 mg po every 6 hours prn for an earache. How many tablets would the nurse administer? • 2 • 3 • 4 • 5
Answer B. 3 • Desire/Have × Supply = X is the formula method. Supply : Have :: X : Desire is the proportion expressed as two ratio method. Supply/Have = X/Desire is the proportion expressed as two fraction method • 975 mg/325 mg × tablet = 3 tablets is the formula method. tablet : 325 mg :: 3 tablets : 975 mg is the proportion expressed as two ratio method. tablet/325 mg = 3 tablets/975 mg is the proportion expressed as two fraction method
Question The client is to receive Mycostatin oral suspension 200,000 units po twice a day. The available Mycostatin oral suspension is 100,000 units per mL. How many milliliters of medication would the nurse administer? • 1 • 2 • 3 • 4
Answer • B. 2 • Desire/Have × Supply = X is the formula method. Supply : Have :: X : Desire is the proportion expressed as two ratio method. Supply/Have = X/Desire is the proportion expressed as two fraction method • 200,000 units/100,000 units × milliliter = 2 milliliters is the formula method. milliliter : 100,000 units :: 2 milliliters : 200,000 units is the proportion expressed as two ratio method. milliliter/100,000 units = 2 milliliters/200,000 units is the proportion expressed as two fraction method
Proficiency With Drug Calculations • Practice = Success