Dispensing Techniques

Transcription

1 Dispensing Techniques Compounding and Good Practice 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. 1

2 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. A record must be kept for the personnel involved including the responsible pharmacist. Methodical approach. A. Weighing Class B dispensing balance (torsion balances) have traditionally been used in dispensing. These balances are designed for the weighing of medicinal or pharmaceutical substances required in filling of prescriptions or in a small scale compounding. Electronic balances (digital) are more common nowadays. 2

3 Torbal torsion balance ( class B) and Ohaus electronic balance. Set of metric weights 3

4 A. Weighing When weighing, some important rules to ensure good dispensing practice: 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. Minimum weighable quantity (MWQ) should be considered: If a quantity less than the MWQ needed, it is necessary to: weigh the minimum weight allowable (or more) and make an excess of the product or prepare it by trituration. BA-FP-JU-C B. Measuring liquids Liquid measures : Graduated pipettes Cylindrical measures Conical measures Volume error differentials due to instrument diameters 4

5 Examples of metric-scale cylindrical (A) and conical pharmaceutical graduates (B). BA-FP-JU-C 6/4/2017 B. Measuring liquids.cont., Rules for measurement: Use the smallest measure. Do NOT split measures. Measurement by difference for viscous liquids. Measuring small volumes: by small conical measure, by graduated pipettes, and by trituration. Taring of containers (next slides). 5

6 B. Measuring liquids.cont., Tared containers For what purpose? 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. B. Measuring liquids.cont., Tared containers How 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. 6

7 C. Mixing & Grinding Mortar and pestle A. 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. C. Mixing & Grinding.cont. B. Porcelain or composition mortars and pestles Larger than the glass variety and have a rougher surface. Ideal for: size reduction of solids mixing solids and liquids, as in the preparation of suspensions and emulsions. 7

8 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). Mixing solids with solids: mortar and pestle, doubling up procedure. Mixing semi-solids rubbing them on an ointment slab using a spatula (may need doubling up). The fusion method using a porcelain evaporating basin. D. Filters Equipment Filters are used when clarification of a liquid is required. Filter paper They are mainly made from wooden pulp (cellulose fibers). 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 Includes wide variety of pore sizes and membrane materials (cellulose acetate, cellulose nitrate, polycarbonate, PTFE). 8

9 Equipment D. 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. Notes: A filter with a pore size µm 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 filter with pore size of 5 15 µm requires a vacuum. Filters Sintered glass filter 9

10 E. Heat sources Bunsen (gas) burners Equipment The Bunsen burner, used for heating laboratory equipment and chemicals. The flame can reach temperatures of 1,500 C. E. Heat sources 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. 10

11 SELECTION OF INGREDIENTS Reputable supplier. Competitive prices. Check on expiry dates. Good storage conditions. Variety of forms. Synonyms. SELECTION OF INGREDIENTS Variety of forms: 11

12 Synonyms: Selection of ingredients BA-FP-JU-C SELECTION OF INGREDIENTS 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 (10% v/v) have the same dilution factor to prepare single strength flavored water (0.25% v/v), i.e. 1 part of concentrate plus 39 parts of water to give 40 parts of flavored water. 12

13 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: The following prescription is received: Sodium Bicarbonate Ear Drops BP, Send 10 ml. Formula: Sodium bicarbonate 500 mg Glycerol 3 ml Freshly boiled and cooled water to 10 ml Expiry date. COUNTING DEVICES For Tablets and Capsules Various methods can be used for this counting: The manual method. Counting triangle (for pills) Capsule counter. 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. 13

14 Counting triangle Capsule counter 14

15 Perforated Counting Tray 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 6/4/2017 in extemporaneous dispensing. BA-FP-JU-C 15

16 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. 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. 16

17 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. 17