Pharmaceutical Measurement PDF

Pharmaceutical Measurement  Objectives Describe instruments for volumetric measurement and characterize their differences in application and accuracy. Describe the correct procedure when using a pharmaceutical balance. Define sensitivity requirement and apply it in c...

Pharmaceutical Measurement  Objectives Describe instruments for volumetric measurement and characterize their differences in application and accuracy. Describe the correct procedure when using a pharmaceutical balance. Define sensitivity requirement and apply it in calculations. Perform calculations by the aliquot method. Demonstrate an understanding of percentage of error in pharmaceutical measurement.  Introduction The role of the pharmacist in providing pharmaceutical care includes the ability and responsibility to compound—that is, to accurately weigh, measure volume, and combine individual therapeutic and pharmaceutical components in the formulation and preparation of prescriptions and medication orders. This is important as one incorrect calculation, conversion or measurements will affect a dosage, and can potentially harm a patient. Two of the most crucial steps in compounding any pharmaceutical product are the accurate calculation and measurement of the component ingredients of the formulation. In order to carry out these critical functions, the pharmacist must have a working knowledge of three systems of measurement: the Metric system, the Apothecary system, and the Avoirdupois system.  The Metric System The metric system is a decimal system with all multiples and divisions based on a factor of 10. This system is also the most commonly used system of measurement for pharmacy calculations, as it allows for quick and easy conversions between different systems of measurement. When using the metric system to convert from smaller to larger, a person would simply move the decimal to the appropriate number of places to the left. When converting from larger to smaller, a person would move the decimal the necessary number of places to the right.  Apothecary System The apothecary system is one of the three systems of measurement used in pharmacy calculations, which uses weight and volume as divisions of measurement. This includes measurements of ounces, gallons, pints and quarts. Traditionally, this system originated as the system of weights and measures for dispensing and prescribing medications for apothecaries, the historical pharmacists, and alchemists. Today, pharmacists still commonly use the apothecary system as their main system of measurement.  The Avoirdupois System The Avoirdupois system is a system of weight measurement only. Its basic unit, the grain, is the same as in the Apothecary system.  Interconversions Common Household Imperial Metric Equivalents 1 drop = 1 minim = 0.04 millilitre 1 teaspoonful = 1 fluid drachm = 5 millilitre 1 desertspoonful = 2 fluid drachm =7.5 millilitre 1 tablespoonful = 4 fluid drachm = 15 millilitre 1 wineglassful = 2 fluid ounce = 60 millilitre 1 teacupful = 4 fluid ounce = 120 millilitre 1 Tumblerful = 8 fluid ounce = 240 millilitre  Measurement of Volume Common instruments for the pharmaceutical measurement of volume range from micropipets and burettes used in analytic procedures to large, industrial-size calibrated vessels. The selection of measuring instrument should be based on the level of precision required. In pharmacy practice, the most common instruments for measuring volume are cylindrical and conical (cone-shaped) graduates For the measurement of small volumes, however, the pharmacist often uses a calibrated syringe or, when required, a pipette. Erlenmeyer flasks, beakers, and prescription bottles, regardless of markings, are NOT volumetric glassware, but are simply containers for storing and mixing liquids. The designated volume(s) express the approximate capacity of the vessel. Guidelines for Selecting Liquid Measurement Devices Always select the smallest device (graduate, pipet, syringe) that will accommodate the desired volume of liquid. This will minimize the potential for errors of measurement associated with misreading the scale. Use a graduated pipet, syringe, or calibrated dropper to measure/deliver volumes