Basic Principles of Compounding & Dispensing

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Basic Principles of Compounding & Dispensing:

By Dr. Muhammad Akbar Pharm. D (R. Ph) M. Phil Scholar (MUST) Basic Principles of Compounding & Dispensing


Introduction Compounding includes the preparation, mixing, assembling, packaging or labeling of a drug in response to a prescription written by a licensed practitioner. Extemporaneous compounding is defined as the timely preparation of a drug product according to a physicians prescription, a drug formula, or a recipe in which calculated amounts of ingredients are made into a homogenous (uniform) mixture. Extemporaneous compounding is done when certain medical needs of individual patients cannot be met by the use of an approved commercial drug product.

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Today, most dosage forms of medications are already pre-packaged by the manufacturer and thus the Pharmacist role is more in the redistribution of medications and the clinical aspect of Pharmaceutical Care. The role of the Pharmacy Technician continues to grow as Technicians are taking on more of the dispensing functions once reserved for the Pharmacist alone. Pharmacy Technicians are also doing extemporaneous compounding of medications.

Goals & Objectives:

Goals & Objectives The Pharmacist will have a basic understanding of the following: Compounding (defined) Reasons for compounding Compounding equipment Principles of compounding Calculations involved

Reasons for Extemporaneous Compounding Today:

Reasons for Extemporaneous Compounding Today Unavailable dosages, strengths and routes of commercial products. Dilution of adult doses of medications to Pediatric/Geriatric strengths Conversion of solid dosage forms to solutions or suspensions Combination of topical dermatological products not available by the manufacturer Inactive ingredients of commercial products which may cause allergic reactions in individuals.

The working environment and procedures:

The working environment and procedures Organization: Tidy & organized method Dispensing bench containing different containers and ingredients Selection of correct ingredients Always return the ingredients back to their place SOP’s should be followed Cleanliness/ Hygiene: Dispensing bench, utensils, equipments and containers must be clean. Staff should have high standards of hygiene Documenting, procedures and results: Record must be kept for a minimum of 2 years (Ideally 5 years) It includes formula, calculations, ingredients and quantity used, their source, batch number, and expiry date

Dispensing procedure :

Dispensing procedure

Equipment 1. Balances:

Equipment 1. Balances Class A Prescription Balance The Class A Prescription Balance is a two-pan torsion type balance that utilizes both internal and external weights. The Class A Prescription Balance is used in the Pharmacy setting as a means of determining the weight of a material to be used in the compounding of a prescription or manufacturing of a dosage form. This balance is currently required in all pharmacy settings and must meet the requirements of the National Bureau of Standards (NBS).

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The minimum weight that can be weighed on this balance is 120 milligrams (mg) and the maximum weight is 120 grams (gm) . The Class A prescription balance has a sensitivity of 6 mg that means just 6 mg of a substance will move the pointer of the balance one division off equilibrium or one degree.

Bulk Balance:

Bulk Balance The Bulk Balance or Counter Balance is less accurate than the Class A Prescription Balance and is primarily used to weigh large quantities of material. It has a limit of 5 Kilograms (Kg) and a sensitivity of 100 mg.

Analytical Balance:

Analytical Balance With the advent of new technology, the Analytical Balance is finding its way from Pharmaceutical analytical laboratories into the Pharmacy setting. Due to convenience, precision and accuracy, as well as a sensitivity of a digital readout of 0.1 mg, most pharmacies prefer the use of this balance.

General rules for use and maintenance of weighing equipments:

General rules for use and maintenance of weighing equipments Balances can give incorrect reading due to poor practice or misuse. Following are important points to ensure accurate weighing: Place the balance on a level surface. Balance must be tarred before use. Balance must be placed in a air free place. Always keep the balance pan clean and free from debris. Calibration of balance must be done to ensure its correct working. Never weigh less than minimum or more than maximum weight declared on the balance.

Measuring Liquids:

Measuring Liquids Graduates are used in the measurement of liquids. Most graduates are marked “TD” which means, “to deliver”. This marking indicates that the measurement of this graduate will compensate for the excess liquid that adheres to the surface of the graduate after emptying.

Conical Graduate:

Conical Graduate The Conical graduate has a wide mouth and wide base to allow the stirring of liquids with a glass stirring rod. As the diameter of the graduate increases, the accuracy decreases. The conical graduate varies in size from 10ml to 4000ml.

Cylindrical Graduates:

Cylindrical Graduates The Cylindrical graduate is uniform from top to bottom and is the most accurate graduate for the measurement of liquids.

Graduate measuring:

Graduate measuring Reading must be done at eye level correct reading is the mark at the bottom of the meniscus Meniscus: surface of the liquid that bulges downward

Mortar and Pestle:

Mortar and Pestle The mortar and pestle is used to grind particles into fine powders (trituration). The incorporation of a liquid (levigation) can further reduce particle size. Mortar and Pestles are made of Glass, Porcelain, Wedgwood or Marble. Glass is preferable for mixing liquids and semi-soft dosage forms.


Spatula Spatulas are used to transfer solid ingredients such as powders, ointments, creams to weighing pans. They are also used to mix ingredients together into homogenous mixtures. Spatulas are available in stainless steel, plastic and hard rubber, the type of spatula to use is dependent on what is being transferred or mixed.

Ointment Slabs:

Ointment Slabs Along with the mortar, pestle and spatula, the Ointment Slab is mainstay in the Pharmacy setting. Ointment slabs provide a clean, hard surface for the mixing of compounds. Most ointment slabs are ground glass plates, that provide a non-absorbable surface area. For multiple compounding, many pharmacies purchase Parchment Papers that serve the same purpose when placed over an ointment slab, but are easily disposed of after use without the necessary cleaning involved between mixtures.


Liquids Liquids such as Solutions and Suspensions, are the most common form of compounded medications. A solution is a clear liquid in where the drug is completely dissolved. A suspension is a liquid preparation that contains fine drug particles that are distributed uniformly throughout the solution. The reconstitution of an antibiotic such as Amoxicillin would be an example of a suspension. Suspensions always require shaking before use.

Solids in Liquids:

Solids in Liquids When solids are required in solution, it is important to reduce the particle size of the solid by using the mortar and pestle (trituration). In some cases, the incorporation of other agents are needed to ensure finer particle size and in the case of suspensions, to ensure even distribution of particles. A dilute solution contains a very small amount of particles or solute in solution. A concentrated solution contains large quantities of solute in solution and a saturated solution contains the maximum amount of solute that can be dissolved in a solvent or at a given temperature or pressure.

Ointments / Creams:

Ointments / Creams Ointments and Creams are semisolid dosage forms used for externally. The are often used when the prescribing physician requires the combination of two or more ointments or creams in a specified ratio or the incorporation of a drug into an ointment or cream base. Ointments are characteristically oil based, while creams are water based. Because the direct mixing of ingredients is not always workable, the incorporation of other agents such as a wetting agent or levigating agent is needed to ensure finer particle size.

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Wetting Agents: Displaces air from particles and allows them to mix better Example: Alcohol Levigating Agents: Reduces particle size Example: Mineral Oil, Glycerin Suspending Agents: A thickening agent that gives some structure to a suspension. Allows easy dispersion of particles. Example: Carboxymethylcellulose, Tragacanth

Geometric Dilution:

Geometric Dilution Extemporaneous compounding of ointments and creams oftentimes involves the use of the mortar & pestle, spatula and the ointment slab. The key to a homogenous mixture is to use these tools properly and to incorporate the method of Geometric Dilution in the preparation of all ointment / cream products. Geometric Dilution is the process by which a homogenous mixture or even distribution of two or more substances is achieved. When using this method, the smallest quantity of active ingredient is mixed thoroughly with an equal volume of the diluents or base on the ointment slab. More diluents (base) is added in amounts equal to the volume of the mixture on the ointment slab. This process is repeated until all of the diluents (base) is incorporated in the mixture. This method, though time consuming, will create a homogenous mixture or smooth dispersion of the drug in the ointment/cream base.

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It is generally agreed that pharmaceutical products should be prepared with a low percentage of error. The Official Compendium allows a tolerance of plus or minus 5 percent for most formulas. In some cases, due to time constraints or lack of experience, Geometric Dilution is not used in the Pharmacy setting and mixtures are just mixed together haphazardly. This “slap them together mixture” may result in gritty and scattered powder that fails to blend in the ointment/cream base being used. A non-homogenous mixture can not only pharmacologically affect the therapeutic effect, but can also cause serious topical skin reactions.


Calculations 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 Pharmacy Technician must have a working knowledge of the metric system, ratio & proportion and percentages. With these skills, the Pharmacy Technician should be able to solve almost all extemporaneous compounding calculations accurately.

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