compounding and good practice
- 1. Dispensing TechniquesCompounding and Good Practice By Shaikh Saniya
- 2. Compounding (Extemporaneous Dispensing) • Definition: A small-scale manufacture of medicines from basic ingredients in the community or in hospital pharmacy ( vs. medicines manufactured by the pharmaceutical industry). • Extemporaneous dispensing should only be used when medicines are not available commercially in the market: Low demand. Requires an individualized dose, e.g. paediatric. Requires an individualized formulation for a patient.
- 3. The working environment • Organization • Cleanliness The bench, the equipment, utensils & the container. Lack of cleanliness can cause contamination of the preparation with other ingredients or a microbial contamination. • Appearance A clean white overall, closed, hair tied up. • Documenting procedures and results Keeping comprehensive records for a minimum of 2 years (ideally 5 years) and include the formula, the ingredients and quantities used, their sources, batch numbers and expiry date. The record for a prescribed item should also include the patient and prescription details and date of dispensing. Methodical approach.
- 4. EQUIPMENT A. Weighing • Non-automatic and automatic weighing equipment. • Non-automated dispensing balances include mechanical beam and electronic top-pan balances. • Three types of balances have traditionally been used in dispensing; class A (50mg to 1g), class B (the most commonly used; 100mg to 50g), and class C (1g to 2kg). • Class B prescription balances are designed for the weighing of medicinal or pharmaceutical substances required in filling of prescriptions or in a small scale compounding. (Also known as Class B dispensing balance).
- 5. EQUIPMENT Torbal torsion balance ( class B) and Ohaus electronic balance.
- 6. EQUIPMENT Set of metric weights
- 7. EQUIPMENT • When weighing, some important rules to ensure good dispensing practice: • Use balances on a level surface (level indicator device). • Balances must be balanced before use, with any indicators reading zero. • Keep the balance in a draught-free environment, clean and free from debris. • When using a top-pan balance, an appropriate container (weighing boat) or piece of paper and auto-zero to cancel its weight. • If using a solid material which requires to be size reduced (ground) or sieved, always ensure that this is carried out before weighing the required quantity. • As far as possible never split quantities and do two weightings, as this will increase the inaccuracies. • If a quantity less than the legal minimum is needed, it is necessary to weigh the minimum weight allowable (or more) and make an excess of the product or prepare it by trituration.
- 8. B. Measuring liquids • Liquid measures: Conical measures and cylindrical measures. • Measuring small volumes: by small conical measure (min. measurable vol for a 10 mL conical is 1 mL), by graduated pipettes (5 mL to 0.1mL), and by trituration (for smaller volumes).
- 9. • The level of liquid is read to the bottom of the meniscus. • The measure is vertical when reading the meniscus; if not considerable errors in quantities can occur especially with conical where the error increases with height because of the slope of the sides. Volume error differentials due to instrument diameters
- 10. EQUIPMENT • Never use more than one measure increases error. • Select the smallest measure that will hold the desired volume. • The measure is thoroughly drained (material can be left in the measure). • If the substance being measured is so viscous difficult to drain the measure effectively measurement by difference (pouring excess into the measure and then pouring off the liquid until only excess volume remains). • Rules for good dispensing practice (label position and the cap of the container).
- 11. C. Mixing & Grinding Mortar and pestle Glass mortar and pestle • Used for small quantities: Useful for dissolving small quantities of ingredients, for mixing small quantities of fine powders • Suitable for size reduction of friable materials (such as crystals). • Used for the mixing of substances such as dyes which are absorbed by and stain composition or porcelain mortars.
- 12. Porcelain or composition mortars and pestles • Larger than the glass variety and have a rougher surface. • Ideal for size reduction of solids and for mixing solids and liquids, as in the preparation of suspensions and emulsions. • For size reduction select proper type. • For mixing purposes: - sufficient space is required for adequate mixing - Rotate pestle in both directions
- 13. EQUIPEMENT Filters Filters are used when clarification of a liquid is required. Filter paper • Filter paper has the disadvantages of introducing fibers into the filtrate and may also absorb significant amounts of active ingredient. Such disadvantages are less likely to happen with the following types. Membrane filters Sintered glass filters • These do not shed fibers, are easy to clean and can be used for substances which attack filter paper such as potassium permanganate and zinc chloride. A filter with a pore size 15–40 µm (grade 3) is suitable for most solutions. They will pass through by gravity, although large volumes may be slow and need the assistance of a vacuum. A grade 4 filter (pore size 5–15 µm) requires a vacuum.
- 15. EQUIPMENT D. Heat Sources •Bunsen (gas) burners The Bunsen burner, used for heating laboratory equipment and chemicals. The flame can reach temperatures of 1,500°C/2,732°F and is at its hottest when the collar is open.
- 16. EQUIPMENT • Water-baths: These are used when melting ointment bases or preparing suppositories • Electric hot plates: Used for melting and heating and have the advantage of thermostatic controls.
- 17. Manipulative techniques Correct equipment + Appropriate technique = Good Compounding Practice * Mixing The goal of any mixing operation should be to ensure that even distribution of all the ingredients has occurred. •Mixing of liquids: Simple stirring or shaking (the degree depends on the viscosity of liquids). •Mixing solids with liquids: stirring rod (solution), pestle and mortar (suspension). Consider size reduction to speed up dissolution process or enhance the distribution of solid through out the liquid. •Mixing solids with solids: mortar and pestle, “doubling up” procedure. •Mixing semi-solids rubbing them on an ointment slap using a spatula (may need doubling up). The fusion method using a porcelain evaporating basin.
- 18. SELECTION OF INGREDIENTS • Reputable supplier. • Good storage conditions. • Check on expiry dates. • Variety of forms. • Synonyms.
- 19. SELECTION OF INGREDIENTS • Variety of forms: BA-FP-JU-C
- 20. Selection of ingredients • Synonyms: BA-
- 21. Concentrated waters • Liquid preparations for oral use are often flavored to make them more palatable for the patient. In extemporaneously prepared products the flavoring is frequently a flavored water, e.g. peppermint water, aniseed water. • All concentrated waters have the same dilution factor, i.e. 1 part of concentrate plus 39 parts of water to give 40 parts of flavored water.
- 22. PROBLEM SOLVING IN EXTEMPORANEOUS DISPENSING• ‘Official’ preparations • The application of simple scientific knowledge; physical properties. • Solubility: are the ingredients soluble in the main vehicles, the particle size, are they present in a lumpy or granular form. If the substance is not soluble, a suspension or an emulsion where one material is an oil will be produced. • Volatile ingredients • Viscosity • Expiry date. e.g. The following prescription is received: • Sodium Bicarbonate Ear Drops BP, Send 10 mL. • Formula: Sodium bicarbonate 500 mg (sol 1 in 11 of water) Glycerol 3 mL (viscous liquid) Freshly boiled and cooled water to 10 mL (quantity of water in ear drops is app. 6.5 mL)
- 23. COUNTING DEVICES For Tablets and Capsules • Various methods can be used for this counting: • The manual method. • A counting triangle (for pills) and capsule counter are the best. • A perforated counting tray. • An electronic counter: Electronic balances, Photoelectric cell counters. • medicines must not be touched by hand. • The equipment should also be carefully cleaned before use.
- 25. Capsule counter
- 27. Key Points • Extemporaneous dispensing should only be used when manufactured medicines are not available. • Accurate dispensing requires clean, neat methodical work. • Comprehensive records of extemporaneous dispensing are required to be kept for at least 2 years. • Electronic balances are increasingly being used in extemporaneous dispensing.
- 28. Key Points • Do not use a balance to weigh less than its minimum weighable quantity. • Ensure that liquid measures comply with the Weights and Measures Regulations. • Always use the bottom of the meniscus when measuring liquids. • Viscous liquids should be measured ‘by difference’. • Pipettes are used to measure volumes between 0.1 mL and 5 mL.
- 29. Key Points • Select the smallest measure for the volume of liquid to be measured. • A glass mortar and pestle can be used for size reduction of friable materials and mixing small quantities of fine powder. • A porcelain mortar and pestle is used for larger quantities, for mixing solids and liquids, making emulsions and for size reduction. • ’Doubling-up’ is used for mixing a small quantity of powder with a larger quantity.
- 30. Key Points • Confusion can arise with different forms of the same material and the use of synonyms. • Concentrated waters are diluted 1 part with 39 parts of water for use as single strength. • Simple problem-solving techniques can produce a satisfactory method of dispensing a product. • Tablets and capsules can be counted manually, or by using a triangle, capsule counter, counting tray or an electronic counter. • Tablets and capsules should not be counted in the hand.
Editor's Notes
- #4: The environment in which you work will have considerable influence on your efficiency and therefore it is important to develop a tidy and organized method of working. The pharmacist who works with a dispensing bench cluttered with several containers all containing different ingredients is more likely to select the incorrect one. Always return ingredients to their appropriate shelf when you have measured out the required quantity.
- #9: Measuring small volumes It is important to select the correct equipment when measuring. The minimum measurable volume for a 10 mL conical measure is 1 mL. Graduated pipettes can be used for volumes from 5 mL down to 0.1 mL. For volumes smaller than this a trituration should be made. The viscosity of the substance being measured should also be considered. Correct use of pipettes. Pipettes can be either the ‘drainage’ or ‘blow-out’ variety. A rubber bulb or teat should be used. Never use mouth suction. • A bulb or teat should be placed over the mouth of the pipette, taking care not to push it down too far. • The container of the substance to be measured should be ready on the bench. • The top of the container should be removed and held in the hand, between the fourth finger and the palm of the hand. • The pipette should be put into the container, taking care that only a short length of the pipette is immersed. If a quantity of liquid is allowed to collect on the outside of the pipette the accuracy of the measuring will be affected. • The correct amount of liquid should then be drawn up the pipette. Take care at this stage as the liquid may shoot up the pipette into the bulb. • If a pipette bulb is being used the appropriate valve is pressed to prevent the liquid running out of the pipette, the pipette is removed from the container and the liquid then released into the desired container. • If using a simple teat this should now be flicked off with the thumb and a finger placed firmly over the top of the pipette, taking care not to allow any liquid to be lost. The pipette can then be withdrawn from the container and the liquid measured out by removing the finger from the top of the pipette. Tared containers Liquid preparations should as far as possible be made up to volume in a measure. There are, however, instances when accurate transfer of the preparation to the final container is difficult. With some suspensions it can be almost impossible to remove all the insoluble ingredients when pouring from one container to another. Emulsions and viscous preparations can also be difficult to transfer accurately. In these cases a tared container should be used. To tare a bottle A volume of water identical to the volume of the product being dispensed is accurately measured. This is then poured into the chosen medicine container and the meniscus marked with the upper edge of a small adhesive label, effectively making the bottle into a single-point measure. The container is then emptied and allowed to drain thoroughly. The preparation is then poured into the container and made up to volume, using the tare mark as the guide. This procedure should be used with discretion and only in situations when major inaccuracies would occur in the transfer of liquids. It should also only be used when water is present as one of the ingredients. Putting medicines into a wet bottle is generally considered bad practice.
- #18: • Place the bases in a porcelain evaporating basin and gently heat them over a water-bath until they have just melted. Excess heat should not be used as overheating may cause physical or chemical changes in some materials. • The basin is then removed from the heat and the contents are stirred continuously, but gently, until the mixture has cooled and set. Stirring at this stage is of vital importance as otherwise the components may segregate on cooling. When using the fusion method do not be tempted to add any solid active ingredients to the basin before the bases have set. Addition of any further ingredients is best done by rubbing down on an ointment slab