Pharmaceutical Calculations Lec 4 PDF

Middle Technical University Institute of Medical Technology Al-Mansour Department of pharmacy Pharmaceutical Calculations Lec 4 First stage/2nd course/  The Imporatnce of Dilution Dilution is applied mainly to alter the dose or strength of a product. The d...

Middle Technical University Institute of Medical Technology Al-Mansour Department of pharmacy Pharmaceutical Calculations Lec 4 First stage/2nd course/  The Imporatnce of Dilution Dilution is applied mainly to alter the dose or strength of a product. The dilution of a liquid dosage form, as a solution or suspension is done to: provide a product strength more suitable for use by a particular patient (e.g., pediatric, elderly, those in disease states). The diluent is selected based on its compatibility with the vehicle of the original product; For Liquid Dosage Form :aqueous, alcoholic, hydro alcoholic, or other. The dilution of a solid D.F. (as a powder or the contents of a capsule) or semisolid D.F. (as an ointment or cream) also may be done. Pharmacists also may find occasion to dilute concentrated acids, alcohol preparations, or very potent therapeutic agents, to meet special compounding requirements.  Relationship Between Strength and Total Quantity If a mixture of a given percentage or ratio strength is diluted to twice its original quantity, its active ingredient quantity will be the same , but the strength will be HALF (reduced by one half). For ex. if 50 mL of a solution containing 10 g of active ingredient with a strength of 20% or 1:5 w/v are diluted to 100 mL, the original volume is doubled, but the original strength is now reduced by one half to 10% or 1:10 w/v. ( but the quantity 10 g is still the same) By contrast, if a mixture is concentrated by evaporation to one-half its original quantity, the active ingredient will be contained in this new volume and the strength will be doubled. For ex. by evaporation of the solvent (10g in 50mL “20%”)  the volume of the solution is reduced to 25 mL (or one half the original quantity), the 10 g in 25 mL of the active ingredient will indicate a strength of 40% or 1:2.5 w/v. If the amount of (active ingredient) remains constant, any change in the quantity of a solution(or mixture of solids)is Inversely proportional to the percentage (or ratio strength);that is, the percentage (or ratio strength) decreases as the quantity increases, and conversely. This relationship is generally true for all mixtures except solutions containing components that contract when mixed together.