This chapter describes a unique method to calculate the maximum potential error associated with drug dose in pharmaceutical mixtures and unit dosage forms, composed of an infinite number of ingredients that are measured on multiple balances of variable sensitivities, and thus provides instant guidance on the pharmaceutical ingredient preparation. The method also determines the sensitivity of the instruments measuring each of the components and the least allowable weight (LAW) of the drug within the predetermined assay standard. A great variety of solved examples with capsules, creams, and ointments as the finished products are used to demonstrate a step-by-step application of the method. The method was written in such a way to help you better understand the principles of balance operation, comprehend the relationship of the sensitivity requirement (SR) of a balance and the maximum allowable error in the dose, appreciate that sequential measurements carry a complicated error propagation on the result, and sharpen up your critical thinking by having to consider all possible consequences of any action involved in prescription preparation prior to actually performing relevant calculations. What follows is the description of the aliquot method of weighing based on the LAW as a method that allows weighing a drug quantity smaller than the sensitivity of the balance. Although the concept of the aliquot method of weighing based on the least allowable weight has been around for more than 50 years, this is really the first time that the theory of the method is developed and applied correctly. The method as described elsewhere ignores errors associated with multiple weighing of drug-excipient mixtures, and as a result, the dose error in the final product is underestimated. The topics are advanced but extremely important.
Pharmaceutical measures Maximum allowable error Least allowable weight Sensitivity requirement Scale-up/down method Aliquot method Geometric dilution
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Errors associated with measurements in pharmaceutical mixtures. Description: (a) Maximum potential error (MPE) of drug in mixtures. (b) SR of any balance used to weigh mixture components. (c) LAW of drug in a mixture within MAE (MP4 493977 kb)
Aliquot method of weighing. Description: (a) Description of the method with detailed explanation of the steps involved. (b) Application of the Aliquot method of weighing in compounded prescriptions that call for a drug amount smaller than the LAW at a given MAE (MP4 577462 kb)
Aliquot method of weighing using multiple balances of different sensitivity. Description: (a) Application of an Aliquot method of weighing in compounded prescriptions that call for a drug amount smaller than the LAW at a given MAE using multiple balances of different sensitivity (MP4 657847 kb)
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