Calculate with Confidence Pharmaceutical Computations 5 th edition

Calculate with Confidence (Pharmaceutical Computations) 5 th edition Dr. J. Domenech Mosby items and derived items © 2010 by Mosby, Inc. , an affiliate of Elsevier Inc.

Dosage Calculation Using the Formula Method Unit Three: Chapter 15 Mosby items and derived items © 2010 by Mosby, Inc. , an affiliate of Elsevier Inc.

Dosage Calculation Using the Formula Method: Objectives After reviewing this chapter, you should be able to: 1. Identify the information from a calculation problem to place into the formula given 2. Calculate dosages using 3. Calculate the number of tablets or capsules to administer 4. Calculate the volume to administer for medications in solution

Formula for Calculating Dosages You must use formula consistently and in its entirety to avoid errors Units of measure must be in same system before solving with the formula Memorize the formula

Terms in the Formula D = Desired dose Ordered in unit of measure desired – mg, units, m. Eq H = Strength available Have on hand in unit of measure available – mg, g, units Q = Quantity Unit of measure that carries what is on hand cited in “H” - tabs, m. L, caps x = Unknown Number of “Q”s needed to give the prescribed dose

Steps to Use Formula 1. 2. 3. 4. 5. 6. Memorize or verify formula from resource Place info in formula and label terms Make sure everything is in same system Apply logic test for reasonable answer Calculate Label answer with correct unit of measure Note: Convert apothecary and household to metric equivalents when possible – metric is the principal system used for medications

“Q” Key Points When “Q” is 1 in value, it can be omitted in the equation, but should be included CAUTION: “Q” value must be used when it is greater than 1 “Q” and the unknown “x” will always have the same unit of measure

Convert to Same System First Order: Phenobarbital gr i p. o. at bedtime WRONG! =x RIGHT Conversion: gr i = 60 mg =x

Convert Toward No Decimals Order: Augmentin 0. 25 g p. o. q 8 hr WRONG! =x RIGHT Conversion Factor: 1 g = 1, 000 mg Therefore, 0. 25 g = 250 mg =x X = ½ tab