III. Послетекстовые упражнения. III.1. Изучите следующую таблицу и заполните пропуски названиями основных инертных ингредиентов таблетки.

III.1. Изучите следующую таблицу и заполните пропуски названиями основных инертных ингредиентов таблетки.

Table 1. Common tablet excipients
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Calcium phosphate dihydrate	Cellulose
Calcium sulfate dihydrate	Alginates
Dextrose	Cellulose derivatives
Lactose	Clays
Mannitol	Starch
Sorbitol	Starch derivatives
Starches

Sucrode-based materials	Stearic acid
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	Stearic acid salts
Acacia	Surfactants
Cellulose derivatives	Talc
Gelatin	Waxes
Glucose	PEGs
Tragacanth	. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PVP	Cornstarch
Sodium alginate	Silica derivatives
Starch (paste	Talc
Starch (pregelatinized	. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sorbitol	FD&C and D&C dyes Flavours in two forms: spray-dried and oils Artificial sweeteners Natural sweeteners

D&C = drug and cosmetics; FD&C = food, drug and cosmetics;

PEG = polyethylene glycol; PVP = polyvinylpyrrollidone, more commonly called povidone

III.2. Выберите правильные варианты ответов.

1. The dispensing pharmacist usually blends potent powders with a large amount of diluent by

(A) spatulation

(B) sifting

(D) geometric dilution

2. Which type of paper best protects a divided hygroscopic powder?

(A) waxed paper

(В) glassine

(D) vegetable parchment

3. Which capsule size has the smallest capacity?

(A) 5

(B) 1

(D) 000

4. Divided powders may be dispensed in

(A) individual-dose packets

(B) a bulk container

III.3. Начертите схему, представляющую разнообразие твёрдых дозированных форм и расскажите о преимуществах и недостатках каждой из них.

III.4. Прочтите и переведите письменно этот отрывок текста.

То satisfy the USP standards, tablets are required to pass one of two tests. A weight variation test is used if the active ingredient comprises the bulk of the tablet. A content uniformity test is used if the tablet is coated or if the active ingredient comprises less than 50% of the bulk of the tablet. Many tablets for oral administration are required to pass a disintegration test. Disintegration times are specified in the individual monographs. A dissolution test may be required instead if the active component of the tablet has limited water solubility. Hardness and friability would affect the disintegration and dissolution rates, but hardness and friability tests are in-house quality control tests, not official USP tests.

III.5. Переведите следующие предложения с русского языка на английский.

1. Твёрдые дозированные лекарственные формы включают порошки, таблетки, драже, гранулы и пилюли.

2. Капсулы - это оболочки для дозированных порошкообразных, гранулированных, полужидких и жидких лекарственных веществ для внутреннего применения.

3. Таблетка - наиболее распространённая твёрдая дозированная форма, получаемая прессованием лекарственных веществ или смесей лекарственных веществ и вспомогательных веществ.

4. Наиболее распространённая форма порошков - порошки неразделенные, порошки, разделённые на отдельные дозы и порошки-инсуффляторы.

5. Порошки для наружного применения выписывают неразделёнными на дозы.

6. Смазывающие и улучшающие скольжение вещества обычно включаются в состав таблетки. Кроме того она обычно содержит вкусовые добавки, красители, связующие вещества и вещества, улучшающие растворение.

7. Сейчас пилюли прописывают редко, но некоторые популярные виды изготавливают фабричным способом.

8. Оболочки различных видов наносятся на прессованные таблетки чтобы защитить ингредиенты от порчи, замаскировать вкус некоторых лекарств или контролировать выделение лекарства.

9. Пастилки, или леденцы растворяются во рту, медленно выделяя активно действующее начало лекарства.

10. Таблетки могут покрываться различными оболочками, включая сахарные, кишечно-растворимые и плёночные оболочки. Недостатком сахарных оболочек является увеличение размера и веса таблетки, и длительное время изготовления.

III.6. Просмотрите тексты A-C урока и выберите перечисленные в них преимущества и недостатки каждой из рассмотренных дозированных форм: порошков, пилюль и таблеток. Выпишите их в две колонки под заголовками:

Advantages: Disadvantages:

III.7. Напишите резюме о твердых дозированных формах, включающее наиболее важную информацию (в тексте должно быть не более 100 слов).

III.8. Закончите следующие фразы, описывающие действие лекарств, выбрав под чертой подходящий по смыслу глагол.

_______________	side effects
_______________	pain
_______________	sleep
_______________	with other drugs
_______________	the ability to drive and to operate machinery
_______________	irritation
_______________	fever
_______________	analgesic effect
_______________	blood vessels
_______________	heart rate
_______________	cough
_______________	the enzyme

Глаголы:

to impair, to have, to relieve, to alleviate, to promote, to dilate, to interact, to soothe, to reduce, to produce, to stimulate, to inhibit.

III.9. Составьте перечень лекарств от простуды (в твердой дозированной форме). Расскажите, как они действуют, к какой группе лекарств относятся, нужен ли рецепт для их покупки.

III. 10. К вам пришел пациент, которому нужно безрецептурное лекарство от простуды. Выясните, нет ли у него аллергии на какое-либо лекарство, спросите, принимает ли он уже какое-то лекарство, порекомендуйте ему одно из лекарств из вашего списка, объясните, как нужно принимать его и что нужно делать, если прием лекарства вызовет нежелательные реакции.

Unit nine

Liquid dosage forms

Грамматика

1. Причастие 1 и 2. § 17, 18

2. Придаточные предложения условия и времени. § 18, 15

3. Неопределенно–личные предложения. § 37

I. Предтекстовые упражнения

I.1. Раскройте скобки и согласуйте видо–временные формы глагола внутри этого текста.

Sterility (to mean) the absence of living microorganisms. The term sterile products(to include) products like parenteral preparations, irrigation solutions, and ophthalmic preparations. Parenteral preparations (to be) pharmaceutical dosage forms that (to inject) through one or more layers of the skin.

Sterilization (to perform) to destroy or remove all microorganisms from the product. Sterilization can (to achieve) through thermal, chemical, radioactive, or mechanical methоds. Though thermal and mechanical sterilization (to use) the longest, they (to improve) recently with the introduction of new types of filters and autoclaves. While thermal sterilization (to involve) the use of either moist or dry heat for destruction of microorganisms by cellular protein coagulation, mechanical sterilization (to remove) microorganisms and (to eliminate) particulate matter.

If a pharmacy involved in preparing sterile products not (to have) a special area called a clean room,laminar flow hoods (to be) vital to ensure aseptic preparation. Before vertical laminar flow hoods (to introduce), horizontal laminar flow hoods (to use) in pharmacies for the preparation of sterile products. According to regulations, clean rooms and laminar flow hoods (to inspect) and (to certify) when they first (to install) and at least 6–12 months thereafter.

I.2. Заполните пропуски соответствующей формой глагола, подходящего по смыслу, обращая внимание на видо–временную форму глагола в главном предложении. (Глаголы можно выбрать из списка внизу).

1. An autoclave will be used if moist heat sterilization ... .

2. Less exposure time will be required when a higher temperature ... .

3. The laminar flow hood will not be certified unless it ... all the necessary requirements.

4. The pharmacy will be inspected again after 12 months ... .

5. This product will be damaged if it .... to heat.

6. If other sterilization methods ... to be unacceptable, gas sterilization of the product will be used.

(to prove, to require, to use, to meet, to pass, to expose)

I.3. Переведите следующие вводные фразы, начинающие неопределенно–личные предложения.

Установлено, что (to determine)

Доказано, что (to prove)

Обнаружено, что (to find)

Замечено, что (to note)

Известно, что (to know)

Подсчитано, что (to estimate)

Считается, что (to believe)

Продемонстрировано, что (to demonstrate)

I.4. Переведите следующие неопределенно–личные предложения на русский язык.

1. In 1935 it was discovered that sulfanilamide stopped the growth of bacteria.

2. It is known that adult drug dosages cannot be extrapolated to children.

3. It is proved that one Zovirax 800 mg tablet is bioequivalent to four Zovirax 200 mg capsules.

4. It is noted that dosage requirements may vary with age, sex, and the patient’s condition.

5. It is established that glucose can be replaced with either sucrose or rice powder which are cheaper.

6. You can find herbs and herbal combinations in tablet, capsule, powdered, and dried form.

7. You should consult a physician if you suffer from any health problem.

8. One can mix the dried herb or herbs with a little water or use a paste with flour or bran.

9. One must be careful when using ophthalmic agents.

10. It is known that sodium is necessary for maintaining the proper water balance and blood pH.

11. What you can safely mix adaptogens with is other adaptogens.

I.5. Подчеркните в каждом предложении места, где пропущены союзы. Назовите их (союзы). Переведите эти предложения.

1. It is obvious the dosage should be reduced in elderly patients.

2. Everybody knows sodium reacts with acids and dissolves in mercury, forming amalgams.

3. The doctor said treatment could be resumed following a 1 to 4 months respite.

4. The side effects this drug may bring about are mild.

5. A finely powdered drug a suspension contains is dispersed in a liquid vehicle.

6. The components the finished dosage form contains are the API and non–drug ingredients (excipients).

7. Research findings show aspirin plays a role in cardiovascular health.

8. Cataracts are the most common eye problem people over 65 suffer from.

9. The amount of vitamins you take should be based on your body’s requirements.

I.6. Определите функцию причастия в этих предложениях. Переведите эти предложения на русский язык.

1. The drug taken orally is poorly absorbed.

2. Antibiotics are normally beneficial and often life-saving.

3. Some life-threatening diseases are now treated with biotechnology products.

4. Solutions applied to wounds, burns, or broken skin should be sterile.

5. The mixture can be harmful to people with pre-existing diseases.

6. Many fluid extracts are considered too potent for self-administration by patients, so they are almost never sold as OTC drugs.

7. Because of their high alcohol content, fluid extracts are sometimes referred to as 100% tinctures.

8. Insoluble powders are reduced to a fine powder and then added to the base, using geometric dilution method.

9. All of the B vitamins have a calming effect on the body and they are synergistic with each other.

10. The recommended starting dose of the drug is 3 tablets taken twice a day with meals or 6 tablets once a day with a meal.

11. Taken orally, intravenously, through an enema or in a suppository, steroid agents can cause serious adverse effects including an increased risk of infection.

12. Camphor has a healing, soothing and tightening effect on the skin.

I.7. Прочтите эти вопросы и отметьте номера тех, на которые вы можете ответить. Ответы на остальные вопросы вы можете найти в текстах этого урока.

1. What is a pharmaceutical solution?

2. How are pharmaceutical solutions broadly classified?

3. Are the words spirit and alcohol synonyms?

4. What methods of preparind liquid dosage forms do you know?

5. Why are some drugs used in injection form?

6. What liquid dosage forms must be sterile and why?

7. What is the difference between solutions and dispersions?

8. What requirement must all colloidal dispersions meet?

9. What two phases do pharmaceutical emulsions consist of?

10. What is required to prepare an emulsion?

II. Работа с текстом.

II.1. Ознакомьтесь со словами к тексту А.

liquid[΄lIkwId]	жидкий
to dissolve, solvent[dI΄zOlv], [΄sOl@nt]	растворять, растворитель
to disperse[dIs΄p@:s]	диспергировать
suitable[΄sju:t@bl]	подходящий
mutually miscible[΄mjutSu@lI΄ mIsIbl]	взаимосмешиваемый
uniformity[junI΄fO:mItI]	однородность, равномерность
solubility[sOlju΄bIlItI]	растворимость
sterile[΄steraIl]	стерильный
ophthalmic[Of΄T{lmIk]	глазной
to observe the rules[@b΄z@:v]	соблюдать правила
aromatic waters[{rou΄m{tIk]	ароматизированные воды (растворы)
spirits[΄spIrIts]	спиртовые растворы
elixirs[I΄lIks@z]	эликсиры
hydroalcoholic[haIdro(u)@lk@΄hOlIk]	водно–спиртовый
maceration[me΄Is@΄reIS@n]	вымачивание
percolation[p@:k@΄leISen]	процеживание
tinctures[΄tlÎktS@z]	настойки
non–volatile[΄nOn ΄vOl@taIl]	нелетучий
a residue[΄rezIdju:]	осадок
to clarify[΄kl{rIfaI]	осветлять (жидкость)
to subside, subsidence [s@b΄saId], [΄söbsId@ns]	осаждать, оседание
to wet, to moisten[΄mOIst@n]	увлажнять
perforated false bottom	перфорированное дно
a tap, a percolator	кран, перколятор
sufficient[s@΄fISI@nt]	достаточный
to saturate[΄s{tSureIt]	насыщать
to drip[drIp]	капать
ether[΄i:T@]	эфир (простой)
collodion[k@΄loudI@n]	коллодион
viscous[΄vIsk@s]	вязкий
digestive[dI΄dZestIv]	пищеварительный
free from microorganisms	не содержит микроорганизмов

II.2. Прочтите текст А и выделите в нем ключевые подтемы. Переведите письменно последний абзац текста.

Text A

Solutions

USP defines solutions as liquid preparations that contain one or more chemical substances dissolved (i.e., molecularly dispersed) in a suitable solvent or mutually miscible solvents. Although the uniformity of drug dosage in a solution can be assumed, such parameters as stability, pH, and solubility of the drug or excipients, taste (for oral solutions), and packaging need to be considered.

There are two major types of solutions, sterile parenteral and ophthalmic solutions, and nonsterile solutions, including oral, topical, and otic solutions. Solutions are the easiest of the dosage forms to compound as long as a few general rules are observed, e.g., an optimal solvent for each drug or chemical is chosen, and compatibility of the ingredients is considered. Thus, the solubility characteristics of each drug or chemical must be known.

Many pharmaceuticals are simply solutions of a medicament in water, alcohol, ether, glycerin, or some other solvent. Various flavoured waters (e.g., chlorophorm or peppermint water) may also be used as solvents. After mixing, many solutions require additional treatment such as sterilization or addition of antimicrobial agents, stabilizers, or buffers.

Spirits are solutions of volatile substances in alcoholor a mixture of water and alcohol. Elixirs are clear, sweetened hydroalcoholic liquids for oral use, usually containing potent drugs, or drugs with unpleasant taste. Simple elixirs are prepared by solution, while those made from plant drugs are produced by maceration or percolation (described below). Tinctures, solutions of a nonvolatile substance in alcohol or a mixture of water and alcohol, are manufactured by simple solution, maceration, or percolation.

In maceration, the drug, suitably prepared, is placed, together with the extracting solvent (known as the menstruum) in a closed vessel and left for a defined period, usually three to seven days, with occasional shaking. The product is then filtered, the residue on the filter (known as marc) is pressed to avoid loss, and the mixed filtrates are clarified either by subsidence (settling out) or filtration.

In percolation, the powdered drug is moistened with the extracting solvent, allowed to stand for a defined period, and then carefully packed in a conical or cylindrical vessel with a perforated false bottom and a tap at the base known as a percolator. Sufficient extracting solvent is added to saturate the drug, and, when the liquid begins to drip from the percolator, the tap is closed and sufficient solvent added to form a layer above the drug. Maceration is then allowed to proceed for a defined period (usually 24 hours), followed by slow percolation, more solvent being added as necessary, until the desired volume of percolate is obtained, which is then clarified by subsidence or filtration.

Fluid extracts are solutions, in alcohol, water, ether,or a mixture of these, of the active part of a vegetable drug so prepared that one cubic centimetre of extract has the same strength as one gram of the dry drug. More concentrated than tinctures, fluid extracts are made by percolation or maceration.

Numerous other types of solutions are used in pharmacy, such as collodions (viscous liquids for external application usually consisting of a drug in oil or soap solution).

Some drugs cannot be given orally, because they are decomposed by the digestive processes; these drugs must be administered by injection, intravenously, intramuscularly or subcutaneously (under the skin). It is imperative that such injection solutions be free from microorganisms or toxic agents; other pharmaceutical preparations that must be sterile include eye drops, eye lotions, and eye ointments.

II.3. Найдите в тексте причастие 1 и 2 и определите их функции. Переведите эти предложения, в которых есть причастия.

II.4. Найдите в тексте ответы на следующие вопросы.

1. What is a pharmaceutical solution?

2. What parameters should be considered in preparing solutions?

3. According to what parameter are the solutions divided?

4. Name the three methods of preparing solutions.

5. Describe the maceration method.

6. Which is a slower method, maceration or percolation?

7. What is the difference between tinctures and fluid extracts tinctures and spirits?

8. Why can some drugs NOT be administered orally?

9. What requirement must all injection solutions meet?

II.5. Соедините следующие слова в пары синонимов:

a tap, to settle, to place, marc, to wet, sufficient, to put, liquid, residue, percolator, fluid, enough, clarified, to moisten, clear, to subside.

II.6. Образуйте как можно больше производных от следующих глаголов и существительных:

to prepare; to compose; to pack; a solute; alcohol; taste; to mix.

II.7. Сравните следующие пары слов. Назовите пары слов, обозначающие: а) одно и то же; б) схожие явления; в) разные явления.

adsorption absorption

lyophilic lyophobic

hydrophilic hydrophobic

interaction interreaction

precipitate residue

valence valency

II.8. Ознакомьтесь со словами к тексту В.

to mingle intimately[΄mIÎgl]	образовывать однородную смесь
a dispersed phase[dIs΄p@st΄feIz]	диспергированное вещество
a dispersion medium[΄mi:dI@m]	дисперсионная среда
a true solution[΄tru: s@΄lu:S@n]	истинный раствор
a coarse dispersion[΄kO:s]	грубая дисперсия
a nanometer[n@΄nOmIt@]	нанометр (нм)
an aggregate[΄{grIgIt]	сгусток, масса
a diameter[daI΄{mIt@]	диаметр
a range[΄reIndZ]	диапазон
rigid[΄rIdZId]	строгий, жёстко заданный
co–precipitation[,kouprI΄sIpIteIS@n]	копреципитация, совместное осаждение
consideration[k@n,sId@΄reIS@n]	условие
to shield[SI:ld]	защищать
to enhance[In΄h{ns]	ускорять
sheath[SI:T]	оболочка
to contribute to[k@n΄trIbjut]	способствовать
alternatively[@l΄t@:n@tIvlI]	в качестве альтернативы
feasible[΄fI:zIbl]	возможный
to be substituted for[söbstI΄tjutId]	заменяться (чем–либо)
buffer[΄böf@]	буфер, буферный

II.9. Прочтите и переведите текст В.

Text В

Colloidal dispersions

When two different substances are mixed together so that they mingle intimately, a two–component system is produced. When one component is distributed uniformly throughout the second, the first component is called the dispersed phase and the second, the dispersion medium or continuous phase.Either phase may be solid, liquid, or gas.

Frequently in pharmacy a solid substance is dispersed in a liquid, usually water, and the resulting substance may have the characteristics of either a molecular dispersion (true solution), a colloidal solution, or a coarse dispersion depending on the particle size of the dispersed solid. In true solutions, the dispersed particles are ions or small molecules having particle size less than one nanometer (nm) In colloidal dispersions, the particles are either single, large molecules of high molecular weight (macromolecules) or aggregates of smaller molecules with diameters between 1 nm and 500 nm in size (0.001 – 0.5). In coarse dispersion the particles are greater than 500 nm in diameter. Note that the particle size ranges given are not rigid and overlap does occur between each dispersion class.

The dispersed phase of a colloidal dispersion may be classified as being either lyophilic (solvent–loving) or lyophobic (solvent–hating). If the solvent is water, these classifications are termed as hydrophylic and hydrophobic respectively.

Since a uniform dispersion of particles is important for the diagnostic and therapeutic effectiveness as well as the safety of administration of pharmaceutical colloids, stability against settling or coprecipitation is an important consideration. The addition of a hydrophilic colloid to a hydrophobic one causes the hydrophilic colloid to adsorb onto and completely surround the hydrophobic particles which then take on some of the properties of the hydrophilic colloid. The hydrophilic colloid shields the hydrophobic system from the destabilizing effects of electrolytes; thus the hydrophilic substance is called a«protective colloid». Stability of such a system is enhanced, because in order to precipitate the hydrophobic colloid, both the protective solvent sheath surrounding it and the electric charge must be removed. Gelatin and methylcellulose derivatives are commonly used as protective colloids.

Sometimes in pharmaceutical formulations buffer salts are added to maintain a pH required for product stability. Occasionally such buffers may contribute to potential instability by forming insoluble salts with metallic ions. This problem may occur especially with phosphate buffers since most heavy metal phosphates are insoluble. If an insoluble phosphate salt precipitates from a colloidal dispersion, it may co–precipitate the colloidal particles along with it. To prevent this phenomenon from occurring, chelatingagents may be used that will preferentially complex the metal ions, and thus prevent them from reacting with the phosphate. Alternatively, nonphosphate buffers may be substituted for phosphate buffers, when feasible, to prevent the instability.

II.10. Составьте схему–классификацию типов дисперсионных коллоидных растворов на основании содержания текста.

II.11. Назовите меры, предохраняющие фармацевтические коллоидные растворы от порчи.

II.12. Ознакомьтесь со словами к тексту С.

a droplet[΄drOplIt]	капелька
the former[΄fO:m@]	первый (из 2 вышеупомянутых)
the latter[΄l{t@]	последний (из 2 вышеупомянутых)
aqueous[΄{kwI@s]	водный
lipid[΄lIpId]	жир, жировой
waxes[΄w{ksIz]	воски
an emulsifying agent[I΄mölsISaIÎ]	эмульгатор
primary, primarily[΄praIm@rI]	первичный, главным образом
to determine[dI΄t@:mIn]	определять
preferentially[pref@΄renSI@lI]	предпочтительно
the choice[tSOIs]	выбор
acceptable[@k΄sept@bl]	приемлемый
by themselves[baI D@m΄ selvz]	самостоятельно
alone[@΄loun]	один, в одиночку
to stabilize[΄st{bIlaIz]	стабилизировать
gums[gömz]	смолы
to be suited for[sju:tId]	быть подходящим для
esters[΄est@z]	сложные эфиры
soaps[΄soups]	мыла
incompatible with[ink@m΄p{tIbl]	несовместимый с
sensitive to[΄sensItIv]	чувствительный к
resistant to[rI΄zIst@nt]	устойчивый к
musilage[΄mlu:sIlIdZ]	слизь
in small increments[΄Inkr@m@nts]	с постепенным увеличением
to bring to volume with	доводить до нужного объёма
a homogenizer[hOm@dZI΄naIz@]	гомогенизатор
preservatives[prI΄z@:v@tIvz]	консерванты
to be intended[In΄tendId]	предназначаться
freezing[΄fri:zIÎ]	замораживание

II.13. Прочтите текст С и составьте перечень инструкций по приготовлению эмульсий.

Text C

Emulsions

Emulsions are two–phase systems in which one liquid is dispersed throughout the other liquid inthe form of small droplets. The former is known as the dispersed, internal, or discontinuous phase, and the latter is known as the dispersion medium, external phase, or continuous phase.

In pharmaceutical emulsions, one phase is usually an aqueous solution. The other phase is usually lipid, or oily. The lipids range from vegetable or hydrocarbon oils to semi–solid hydrocarbons and waxes. Emulsions are usually described in terms of water and oil. Oil is the lipid, or nonaqueous, phase regardless of its composition. If water is the internal phase, the emulsion is classified as water–in–oil (w/o). If water is the external phase, the emulsion is classified as oil–in–water (o/w). Correct proportions of oil and water should be used during preparation of emulsions. The internal phase should represent about 40–60% of the total volume.

The two liquids in an emulsion are immiscible and require the use of an emulsifying agent. The type of emulsion formed is primarily determined by the relative phase volumes and the emulsifying agent used. Most agents preferentially form one type of emulsion if the phase volume permits. The choice of an emulsifying agent is more important in determining the final type of emulsion. The effectiveness of an emulsifying agent depends on its chemical structure, concentration, solubility, pH, physical properties, and electrostatic effect. True emulsifying agents (primary agents) can form and stabilize emulsions by themselves. Stabilizers (auxiliary agents) do not form acceptable emulsions when used alone, they assist primary agents in stabilizing the product (e.g., increase viscosity).

Emulsifying agents are either natural or synthetic. Natural emulsifying agents include gums, such as acacia and tragacanth, agar, pectin, gelatin, methylcellulose, and carboxy–methylcellulose. Acacia and tragacanth are used to form o/w emulsions. They are best suited for emulsions intended for internal administration. Synthetic emulsifying agents can be anionic, cationic, or nonionic. Anionic synthetic agents include sulfuric acid esters, sulfonic acid derivatives, and soaps. They have a high pH and are therefore sensitive to addition of acids and electrolytes. Cationic synthetic agents are incompatible with soaps. Nonionic synthetic agent are resistant to the addition of acids and electrolytes.

The order of mixing of ingredients in an emulsion depends on the type of emulsion being prepared (o/w or w/o) and on the emulsifying agent chosen. Medicinal agents can be incorporated into an emulsion either during or after its formation. It is best to incorporate a drug into a vehicle during emulsion formation, when it can be incorporated in molecular form Addition of a drug to a preformed emulsion can present some difficulty, depending on the type of emulsion and the nature of the emulsifier.

Emulsions are prepared by the following four methods: wet gum (English) method, dry gum (continental) method, bottle method and beaker method. The latter is used in preparing emulsions with synthetic emulsifying agents. In the wet gum method, the primary emulsion of fixed oil, water, and acacia (in a 4:2:1 ratio) is prepared as follows:

(1) Two parts of water are added all at once to one part of acacia. The mixture is triturated (A rapid motion is essential when triturating the ingredients using a mortar and pestle). The mixture is triturated until a smooth musilage is formed.

(2) Oil is added in small increments (1–5 ml) with continuous trituration until the primary emulsion is formed.

(3) The mixture (an o/w emulsion) is triturated for another 5 minutes.

(4) The mixture can be brought to volume with water, and a hand homogenizer or an electric mixer is used to obtain the final product.

Emulsions are unstable, and addition of preservatives is required if the preparation is intended for use longer than a few days. Generally, a combination of methylparaben (0.2%) and propylparaben (0.02%) is used. The product should be protected from light and extreme temperatures. Both freezing and heat may have an adverse effect on the product stability. A «shake well» label should be placed on the final product.

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