Pharmaceutical Compounding and Dispensing
Pharmacists or their pharmaceutical equivalents have been responsible for compounding medicines for cen-turies. Recently this role has been challenged in the pharmaceutical literature with suggestions and recom-mendations that it is inappropriate for the pharmaceu-tical practitioner to compound medicines in a local pharmacy environment. Notwithstanding this valid debate, it is clear that a vast array of skills and knowl-edge with regard to medicines’ compounding has been accrued and refined, certainly over the last two centu-ries. In the present environment it is possible that this knowledge and skill base might be dispersed and ulti-mately lost. However, it is not beyond the bounds of imagination to conceive that there will be times, albeit possibly in the face of some form of environmental, cultural or local emergency, when pharmacists might be called upon to extemporaneously compound med-icines when conventional supply chains are either unavailable or have broken down.
This text has been designed with a number of func-tions in mind. First, it is important to be aware of some of the historical pathways that have led to the present technological position of pharmacists. In addition, unless many of the antiquated measuring systems, methodologies and formulations are preserved in some reference work, they might be lost forever, or at least be totally unavailable except to the dogged historian. Primarily, however, this work is intended as a reference-based tutorial to the methods employed in medicines’ compounding. The text has been designed to allow students and practitioners to be able to exam-ine either all or part of the subsequent chapters in order to familiarise themselves with the compounding tech-niques necessary to produce products of appropriate quality and efficacy. In addition, the text is supported by moving images in order to augment the necessary techniques and expertise.
The text also has a role when considering the design and implementation of standard operating pro-cedures (SOPs) pertinent to certain sectors of profes-sional practice today. Although we do not expect all practitioners of pharmacy to be compounding medi-cines on a daily basis, we hope that should the need arise this text will effectively support any work of this nature that might be encountered.
This second edition has updated the first edition and, to assist the student compounder, the text now includes examples of the pharmaceutical label for each worked example.
History of compounding
It is impossible to determine when humans first began to mix substances and concoct preparations that pro-duced either perceived or real therapeutic effects, but it is known that the compounding of medicinal prepara-tions from materia medica of animal, vegetable and mineral sources has been practised in a sophisticated form by a range of ancient civilisations. The societies of Ancient Egypt, Greece, Rome and the Arabian cul-tures, for example, all developed complex levels of medical knowledge, integrating various aspects of pharmacy and medicines compounding.
The Ancient Egyptian cultures exerted an influ-ence upon social and scientific development through-out the period extending from approximately 3000 BC to 1200 BC. Clearly, throughout this period of diverse cultural development, Egyptian society was supported by specialist medical and pharmaceutical practice. Archaeological research shows widespread evidence of medicines compounding being central to the thera-peutics practised by the Ancient Egyptians. Examples of medicines’ chests containing dried drugs and the tools associated with compounding have been found. Written works on papyrus have also been discovered that describe contemporary materia medica, formulae, remedies and the weights and measures used. Many of the vegetable-based drugs, animal products and minerals described are recognisable today, and indeed some remain in current use.
Prepared drugs were also a feature of the various Mesopotamian civilisations that existed in parallel with the Egyptian cultures. Again, some of the drugs used by the Assyrians, such as opium, myrrh and liquo-rice, are still used today.
The Ancient Greek civilisations made known con-tributions to medicine and pharmacy principally between approximately 1250 BC and 285 BC. It would appear that the Ancient Greek medical practice used fewer drug-based therapies than the Egyptian and Mesopotamian cultures. Despite this, around 400 drugs are described by Hippocrates, writing around 425 BC. Interestingly, Hippocrates also emphasised the importance of pure water in medicine and the necessity for absolute cleanliness in surgery, features that are still causing problems in the treatment of patients today.
After the disintegration of the Ancient Greek civ-ilisation around 220 BC, many Greek physicians moved either to Rome or to other parts of the Roman Empire. Prior to this period Roman medical and pharmaceutical practice had revolved around reli-gious and superstitious ritual, principally conducted by the lower sections of society such as slaves (servi medici) and wise-women (sagae). Drugs and prepared medicines were used by the Romans, but compound-ing again appeared to be chiefly carried out by less prominent sections of society, with herb-gatherers (rhizotomi), drug pedlars (pharmacopoloe) and those trading in salves (unguentarii) being in evidence.
By around 30 BC, under the influence of imported Greek practice, the status of some of those practising medicine had risen, and until the fall of the Roman Empire a substantial number of influential practi-tioners were in evidence, including Celsus, Dios-corides and Galen. Each of these great practitioners left written works containing information on drugs, medicines and compounding, which formed the basis of therapeutics well into the seventeenth century.
As the Roman Empire disintegrated, the West entered the Dark Ages and medical and pharmaceuti-cal practice was transformed into a ‘monastic’-driven system. During this time, although some Graeco-Roman therapeutic principles were preserved, practice was largely based upon religious and superstitious beliefs. By contrast, in the Eastern Byzantine area of the Roman Empire, centred on Constantinople, which remained until 1453, much of the classical literature on therapeutics and drug trading links was retained. An additional eastern repository and incubator of medical knowledge developed in Arabia during the Dark Ages. Traditional Graeco-Roman medical texts were translated into Arabic and compiled with other works collected from the Far East. The Arabs of this period also derived information from their studies on alchemy.
Pharmaceutical forms and their preparation
It is necessary to master a number of key formulation skills in order to be able to produce accurate and effica-cious extemporaneous preparations. This chapter out-lines the key basic concepts and calculations that will be used throughout this book. All practitioners, irrespective of their own individual area of practice, must become competent in the key skills outlined in this chapter.
Weights and measures
Weighing and measuring are possibly the two most fundamental practical skills practised by a com-pounder. During compounding, ingredients will need to be either weighed or measured and the accuracy of the compounder’s technique will have a great bearing on the accuracy and efficacy of the final product.
Weighing
When weighing pharmaceutical substances, the Systeme International d’Unites (SI) based around the gram (g), is the system that is used. Variants on the base unit are formed by 1000 times increases or divisions of the gram. Table 4.1 summarises the main units used within the pharmaceutical profession. For weights less than 1 mg, the units of the weight are usually written in full (for example 1 nanogram rather than 1 ng, or 3.4 micrograms rather than 3.4 mg). This is because the first letter of the abbrevi-ation (the m or n) when written by hand may be mis-taken for the letter ‘m’. This could then result in dosing errors of one-thousand times plus.
Conversions between the main weighing units are essentially easy as they are all based around 1000 times multiplications or divisions of the base unit. However, care must be exercised in carrying out these calcula-tions as errors may not be immediately obvious.
Balances
When weighing a pharmaceutical ingredient or product, it is important to select the correct balance. Different types of balance are designed to weigh within different weight ranges to differing degrees of accuracy. For example, a balance designed to weigh 5 kg to an accuracy of 0.01 kg (10 g) is not going to be suitable to weigh 200 mg (0.2 g).
Broadly speaking, there are likely to be three dif-ferent types of balance that will be encountered in a pharmaceutical environment. These are:
* the Class II balance or electronic equivalent
* sensitive electronic balances
* balances for weights greater than 50 g.
Product formulae
As a result of recent changes in pharmaceutical prac-tice it is becoming less common for pharmacists, espe-cially within a primary care setting, to compound extemporaneous products for patients. This has resulted in a comparable decline in the inclusion of extemporaneous formulae in modern official text books.
To assist the compounder in their choice of formu-lation for an extemporaneous product, this part of the book contains a selection of extemporaneous formu-lae. These are a mixture of old formulae that are now rarely used but which still have a place in therapeutics along with some formulae that have been derived from old texts.
Formulae contents
The following index lists, in alphabetical order, prod-uct formulae contained in all three parts of the book. The source of each formula is included with its entry.
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