VPT 311: General and Systemic Veterinary Pharmacology (2+1)

STRENGTH OF PREPARATIONS 

1. Ratio strength
• One of the ways of expressing strength of solutions. Phrase such as 1 in 10 means 1 part by volume (liquid) or by weight (solid) is to be diluted with solvent to make the final product 10 parts by volume. E.g., 1 in 10 means 1 g of solid or 1 ml of liquid to be dissolved in to make a final volume of 10 ml of solution.
2. Percentage solution
• Most commonly used for expression of preparations. It is written as % and it means per hundred. The percentage of an ingredient in 100 parts of the preparation. It is a type of ratio and has no units. Percentage can be expressed in 3 different ways.
• Weight by weight (w/w): g / 100 g. Used to express solids in solids for use of powders, ointments etc.
• Weight by volume (w/v): for percentage of solids in liquids. The most common type used in pharmacy to express solids dissolved in solvents. Since most often solutions in pharmacy are dissolved as ‘mg per ml’, for a common conversion of w /v percent solution, multiply % (number value) by 10 to get the value in mg per ml.
• Volume by volume (v/v): for percentage solutions where both the ingredient and the solvent are taken in volume measures and are liquid in nature.e.g., preparation of emulsions, spirits etc.
3. Trituration
• Trituration is also used in pharmacy to indicate w/w expressions especially in pharmacy. A 1 in 10 trituration means 1 g of solid diluted with another solid to make the total weight to 10 g
4. Parts per thousand
• A common way of expression of very dilute solutions. 1 part per thousand means dilution to the tune of 1 gram in 1000 ml of diluent (only used to express w/v solutions).
5. Parts per million (ppm)
• This is commonly used to indicate very dilute solutions. 1 part per million indicates one part of the solute or drug in one million parts of the solution.(w/v or v/v). This expression is also commonly used to express the strengths of drug residues or toxicants