Basics of Compounding: Using Chemical Conversion Factors
Author(s): Fonseca Simonne C
Issue: Sep/Oct 2005 - Pain Management
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Abstract: Several factors related to the chemical ingredients should be considered when performing pharmaceutical calculations prior to compounding in the pharmacy. Some factors need to be accounted for and corrected in calculations and others do not. If these variables are not considered, the final drug concentration in the preparation may be out of the allowable range. This article summarizes the importance of assay value, loss on drying, water of hydration, and base and salt or ester conversions and how to calculate these conversions. Even though assay value and loss on drying are not converted in values before compounding, it is important to explain and compare them to the variables that should be converted. The only assay values that must be converted are those that have a specific value that has been provided by the manufacturer of the chemical, such as gentamicin sulfate, where a “potency equivalent” is provided on the label by the manufacturer.
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