Liquid Dosage Forms

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Liquid Dosage Forms
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1. Pharmaceutical Solutions
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Solutions are Dosage forms prepared by
dissolving the active ingredient(s) in an
aqueous or non aqueous solvent.
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Solutions can be formulated for different routes
of administration Orally Syrups, elixirs,
drops In mouth and throat Mouth washes,
gargles,
throat sprays. In body cavities Douches,
enemas, ear drops,
nasal sprays. On body Surfaces Collodions,
lotions.
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Advantages of SoIutions (1) Easier to swallow
therefore easier for children - old age -
unconscious people. (2) More quickly effective
than tablets and capsules. (3) Homogenous
therefore give uniform dose than suspension
or emulsion which need shaking. (4) Dilute
irritant action of some drugs (aspirin, Kl, KBr)
minimize adverse effects in the GIT like KCl.
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• Disadvantages of SoIutions
• Bulky therefore difficult to transport and
  store.
• (2) Unpleasant taste or odours are difficult to
  mask.
• (3) Needs an accurate spoon to measure the dose.
• (4) Less stable than solid dosage forms.
• major signs of instability
• colour change,
• precipitation
• microbial growth
• chemical gas formation

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• Additives
• Buffers
• To resist any change in pH
• Isotonicity modifiers
• Solutions for injection
• Application to mucous membrane
• Large-volume solutions for ophthalmic
  application
• Most widely used isotonicity modifiers are
  dextrose and NaCl
• Viscosity enhancement
• It is difficult for aqueous-based topical
  solutions to remain on the skin or in the eye
  (why?) therefore low concentrations of jelling
  agents are added to increase the viscosity of the
  product.

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• Preservatives
• Solution may become contaminated for a number of
  reasons
• Raw materials used in the manufacture of
  solutions are excellent growth media for
  bacterial substances such as gums, dispersing
  agents, sugars and flavors
• Equipment, environment and personnel contribute
  to product contamination.
• Consumer use may result in the introduction of
  microorganism.
• ? a preservative should be added to the
  product
• Preservative used should be
• effective against a wide spectrum of
  microorganisms
• stable for its shelf life
• non toxic, non sensitizing
• compatible with the ingredients in the dosage
  form
• free of taste and odour

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• Preservatives may be used alone or in combination
  to prevent the growth of microorganisms.
• Alcohols
• Ethanol is useful as a preservative when it is
  used as a solvent.
• It needs a relatively high concentration (gt
  10) to be effective.
• Propylene glycol also used as a solvent in oral
  solutions and
• topical preparations. It can function as a
  preservative in the
• range of 15 to 30. It is not volatile like
  ethanol.
• Acids
• Benzoic acid and sorbic acid have low solubility
  in water.
• They are used in a concentration range from 0.1
  to 0.5.
• Only the non-ionized form is effective and
  therefore its use is
• restricted to preparations with a pH below
  4.5 (WHY?).

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• Esters
• Parabens are esters (methyl, ethyl, propyl and
  butyl) of p-hydroxybenzoic acid.
• They are used widely in pharmaceutical products
  and are effective and stable over a pH range of 4
  to 8.
• They are employed at concentrations up to about
  0.2. Frequently 2 esters are used in combination
  in the same preparation WHY?
• To achieve a higher total concentration
• To be active against a wider range of
  microorganisms.
• Quaternary Ammonium Compounds
• Benzalkonium chloride is used at a relatively low
  concentration 0.002 to 0.02.
• This class of compounds has an optimal activity
  over the pH range of 4 to 10 and is quite stable
  at most temperatures.
• Because of the cationic nature of this type of
  preservative it is incompatible with many anionic
  compounds.

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• Antioxidants
• Vitamins, essential oils almost all fats and
  oils can be oxidized. Oxidation reaction can be
  initiated by
• 1. heat maintain oxidizable drugs in a cool
  place
• 2. light use of light- resistant container
• 3. heavy metals (e.g. Fe, Cu) effect of trace
  metals can be
• minimized by using citric acid or
  ethylenediamine tetraacetic
• acid (EDTA) i.e. sequestering agent .
• Antioxidants as propyl octyl esters of gallic
  acid, tocopherols or vitamin E, sodium sulfite,
  ascorbic acid (vit. C) can be used.
• Sweetening agents
• Sucrose is the most widely used sweetening agent.
  
• Advantages Colourless, highly water soluble,
  stable over a wide pH range (4-8), increase the
  viscosity, masks both salty and bitter taste, has
  soothing effect on throat.
• Polyhydric alcohols (sorbitol, mannitol and
  glycerol) possess sweetening power and can be
  used for diabetic preparations.

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• Flavours and perfumes
• Mask unpleasant taste or odour
• Enable the easy identification of the product.
• Natural products fruit juices, aromatic oil
  (peppermint, lemon)
• Artificial perfumes are cheaper, more readily
  available and
• more stable than natural products.

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Stability of solutions Both physical and chemical
stability of solutions in their containers is
very important A solution must retain its
clarity, colour, odour, taste and viscosity over
its shelf life.
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Classification of Solutions According to Vehicle
(a) Aqueous solutions (b) Non-aqueous
solutions Aqueous Solutions Aqueous
solutions are homogeneous mixtures that are
prepared by dissolving a solid, liquid or gas in
an aqueous medium (vehicle). Vehicle This may
be water, aromatic water or extracts.
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WATER Water is used both as vehicle and as a
solvent for the desired flavoring or medicinal
ingredients. Advantages Tasteless, odourless,
lack of pharmacological activity, neutral and
very cheap Tap Water It is not permitted to
use tap water for the dispensing of
pharmaceutical dosage forms due to its possible
bacterial contamination and the presence of
dissolved salts that destroy the active
ingredients or enhance their decomposition.
Freshly Boiled and Cooled Water Boiling is
seldom used to destroy vegetative bacteria. But,
on storage for long time spores may yield
vegetative microorganism.
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• Purified Water
• Must be used for most pharmaceutical operations
  and in all the tests and assays.
• Such water is prepared by distillation,
  deionization or reverse osmosis.
• "Hard" waters are those that contain the Ca and
  Mg cations.
• Alkaline" waters are those that contain
  bicarbonates as the major impurity.
• Ultraviolet energy, heat or filtration (Millipore
  filtration) can be used to remove or kill the
  microorganisms present in the water.
• Water for injection
• Must be used for the formulation of parental
  solutions.
• It is obtained by sterilizing pyrogen-free
  distilled water.

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• Aromatic Waters
• Aromatic waters (medicated waters) are clear,
  saturated aqueous solution of volatile oils or
  other aromatic or volatile substances.
• They are used principally as flavored or perfumed
  vehicles.
• Volatile oils solutions represent an
  incompatibility problem of
• salting out. This occurs after the
  incorporation of a very soluble
• salt in their solution.
• Aromatic water will deteriorate with time
  therefore
• - should be made in small quantities
• - protected from intense light and excessive
  heat by storing
• in air tight, light resistant containers.
• If they become cloudy or otherwise deteriorate
  they should be
• discarded. Deterioration may be due to
  volatilization, decomposition or mould growth.
• There are 2 official methods of preparation

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• (a) Distillation process (Stronger Rose Water NF)
  
• Adv. most satisfactory method Dis. slow
  and expensive
• The drug should be coarsely ground and mixed with
  sufficient
• quantity of purified water in the
  distillation unit.
• After distillation any excess oil in the
  distillate is removed by
• filtration.
• Drug should not be exposed to the action of
  direct heat during
• distillation otherwise, the odour of the
  carbonized substance
• will be noticeable in the distilled aromatic
  water.
• If the volatile principle in the water are
  present in small
• quantities the distillate is returned several
  times to the still with
• fresh portions of drug.
• (b) Solution process (Peppermint water)
• Aromatic water may be prepared by shaking
  volatile substance with purified water. The
  mixture is set aside for 12 hours filtered.
  Talc (inert) may be used to increase the surface
  of the volatile substance, insure more rapid
  saturation of the water and act as a filter aid.

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• Methods of Preparation of Solutions
• (a) Simple Solution
• (b) Solution by Chemical Reaction
• (c) Solution by Extraction
• (a) Simple Solution
• Solutions of this type are prepared by dissolving
  the solute in a suitable solvent (by stirring or
  heating).
• The solvent may contain other ingredients which
  stabilize or solubilize the active ingredient
  e.g. solubility of Iodine is 1 2950 in water
  however, it dissolves in presence of KI due the
  formation of more soluble polyiodides (KI.I2
  KI.2I2 KI3.I3 KI.4I4) . Strong Iodine
  Solution USP (Lugol's SoIution).

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(b) Solution by Chemical Reaction These solutions
are prepared by reacting two or more solutes with
each other in a suitable solvent e.g. Calcium
carbonate and lactic acid used to prepare Calcium
lactate mixture. WHY? (c) Solution by
Extraction Plant or animal products are prepared
by suitable extraction process. Preparations of
this type may be classified as solutions but more
often, are classified as extractives. Extractives
will be discussed separately.
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• Pharmaceutical Solutions
• Aqueous
• Douches
• Enemas
• Gargles
• Mouthwashes
• Nasal washes
• Juices
• Sprays
• Otic solutions
• Inhalations

• Sweet /or Viscid
• Syrups
• Honeys
• Mucilages
• Jellies

• Nonaqueous
• Elixirs
• Spirits
• Collodions
• Glycerins
• Liniments
• Oleo Vitamin

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Aqueous Pharmaceutical Solutions
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• Douches
• Douche is an aqueous solution, which is directed
  against a part or into a cavity of the body.
• It functions as a cleansing or antiseptic agent.
• Eye douches are used to remove foreign particles
  and discharges from the eyes. It is directed
  gently at an oblique angle and is allowed to run
  from the inner to the outer corner of the eye.
• Pharyngeal douches are used to prepare the
  interior of the throat for an operation and to
  cleanse it in supportive conditions.
• Similarly, there are nasal and vaginal douches.
• Douches most frequently dispensed in the form of
  a powder with directions for dissolving in a
  specified quantity of water.

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• Enemas
• These preparations are rectal injections employed
  to
• evacuate the bowel (evacuation enemas),
• influence the general system by absorption
  (retention enemas) e.g. nutritive, sedative or
  stimulating properties
• affect locally the site of disease (e.g.
  anthelmintic property)
• they may contain radiopaque substances for
  roentgenographic examination of the lower bowel.
• Retention enemas are used in small quantities
  (about 30ml) and are thus called retention
  microenema.
• Starch enema may be used either by itself or as a
  vehicle for other forms of medication

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• Gargles
• Gargles are aqueous solutions frequently
  containing antiseptics, antibiotics and/or
  anesthetics used for treating the pharynx
  (throat) and nasopharynx by forcing air from the
  lungs through the gargle, which is held in the
  throat subsequently, the gargle is expectorated.
  
• Many gargles must be diluted with water prior to
  use. Although mouthwashes are considered as a
  separate class of pharmaceuticals many are used
  as gargles, either as is, or diluted with water.
• The product should be labeled so that it cannot
  be mistaken for preparations intended for
  internal administration.

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• Mouthwashes
• Mouthwashes can be used for therapeutic
  cosmetic purposes
• Therapeutic mouthwashes can be formulated to
  reduce plaque, gingivitis, dental caries and
  stomatitis.
• Cosmetic mouthwashes may be formulated to reduce
  bad breath through the use of antimicrobial
  and/or flavoring agents.
• Mouthwashes are used as a dosage form for a
  number of specific problems in the oraI cavity
  e.g.
• mouthwashes containing
• combination of antihistamines, hydrocortisone,
  nystatin and tetracycline have been prepared for
  the treatment of stomatitis,
• a painful side effect of
  cancer therapy.
• Allopurinol used for the treatment of stomatitis,
  
• pilocarpine for xerostoma (dry mouth)
• tranexamic acid for the prevention of bleeding
  after oral
• surgery.
• carbenoxolone for the treatment of orofacial
  herpes simplex
• infections

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• Mouthwashes generally contain four groups of
  excipients
• AIcohols (10-20 in MW) ? may function as a
  preservative.
• aids in masking the unpleasant taste of active
  ingredients,
• functions as a solubilizing agent for some
  flavoring agents
• Humectants such as glycerin and sorbitol (5-20
  in MW)
• increase the viscosity of the preparation
• enhance the sweetness of the product
• improve the preservative qualities of the
  product.
• Surfactants Non ionic and anionic surfactants
  aid in the solubilization of flavors and in the
  removal of debris by providing foaming action.
  Cationic surfactants such as cetylpyridinium
  chloride are used for their antimicrobial
  properties, but these tend to impart a bitter
  taste.
• Flavours are used in conjunction with alcohol
  and humectants to overcome disagreeable tastes.
  The principle flavoring agents are peppermint,
  cinnamon, menthol or methyl salicylate.
• CoIouring agents also are used in these
  products.

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• Nasal Solutions
• Nasal solutions are usually aqueous solutions
  designed to be administered to the nasal passages
  in drops or sprays.
• Ephedrine Sulfate or Naphaxoline Hydrochloride
  Nasal Solution USP are administered for their
  local effect to reduce
• nasal congestion
• Lypressin Nasal Solution USP for its systemic
  effect for the
• 
  treatment of diabetes insipidus
• The current route of administration of peptides
  and proteins is limited to parental injection
  because of inactivation within the GIT. As a
  result there is considerable research on
  intranasal delivery of these drugs such as
  insulin.
• Intranasal drug administration offers rapid
  absorption to the systemic circulation. This
  route is safe and acceptable alternative to the
  parental administration

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There is a direct route of transport from the
olfactory region to the central nervous system
(CNS) without prior absorption to the circulating
blood. The olfactory receptor cells are in
contact with the nasal cavity and the CNS and
they provide a rout of entry to the brain that
circumvents the blood brain barrier
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• Commercial nasal preparations include
  antibiotics, antihistamines and drugs for asthma
  prophylaxis.
• Current studies indicate that nasal sprays are
  deposited in the pharynx with the patient in an
  upright position.

Pharynx

• Drops spread more extensively than the spray and
  three drops cover most of the walls of the nasal
  cavity, with the patient in a supine position and
  head tilted back and turned left and right.

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• Nasal decongestant solutions are employed in the
  treatment of rhinitis of the common cold and for
  allergic rhinitis (hay fever) and for sinusitis.

Sinuses are air-containing cavities in certain
bones of the skull
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• Their frequent use or their use for prolonged
  periods may lead to chronic edema of the nasal
  mucosa, i.e. rhinitis medicainentosa, aggravating
  the symptom that they are intended to relieve.
  Thus, they are best used for short periods of
  time used for short periods of time (no longer
  than 3 to 5 days).
• Nasal solutions are prepared so that they are
  similar in many respects to nasal secretions, so
  that normal ciliary action is maintained thus
  aqueous nasal solutions usually are isotonic and
  slightly buffered to maintain a pH of 5.5 to 6.5.
  

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• Sprays
• Sprays are solutions of drugs in aqueous vehicles
  and are applied to the mucous membrane of the
  nose and throat by means of an atomizer
  nebulizer.
• The spray device should produce relatively coarse
  droplets if the action of the drug is to be
  restricted to the upper respiratory tract. Fine
  droplets tend to penetrate further into the
  respiratory tract than is desirable.

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• Many of the older sprays were prepared by
  dissolving drug in light liquid petrolatum. This
  vehicle may retard the normal ciliary action of
  the nasal mucosa and if drops of oil enter the
  trachea, can cause lipoid pneumonia. Therefore
  aqueous sprays, which are isotonic with nasal
  secretions and of approximately the same pH are
  to be preferred (WHY?). Such sprays may contain
  antibiotics, antihistamines, vasoconstrictors,
  alcohol, and suitable solubilizing and wetting
  agents.
• They are used for the treatment of allergy and/or
  vasodilatation (congestion) that occur with
  common cold.

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• Otic Solutions
• The main classes of drugs used for topical
  administration to the ear include local
  anesthetics, e.g. benzocaine antibiotics e.g.
  neomycin and anti-inflammatory agents, e.g.
  cortisone.
• These preparations include the main types of
  solvents used, namely glycerin or water.
• The viscous glycerin vehicle permits the drug to
  remain in the ear for a long time.
• Anhydrous glycerin, being hygroscopic, tends to
  remove moisture from surrounding tissues, thus
  reducing swelling.
• Viscous liquids like glycerin or propylene glycol
  either are used alone or in combination with a
  surfactant to aid in the removal of cerumen (ear
  wax).
• In order to provide sufficient time for aqueous
  preparations to act, it is necessary for the
  patient to remain on his side for a few minutes
  so the drops do not run out of the ear.

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For a Middle Ear InfectionWhile the person
receiving Otic solution lies on his/her side, the
person giving the drops should gently press the
(TRAGUS (4 times in a pumping motion. This will
allow the drops to pass through the hole or tube
in the eardrum and into the middle ear.
For an Ear Canal Infection While the person
receiving the medication lies on his/her side,
the person giving the drops should gently pull
the outer ear upward and backward. This will
allow the ear drops to flow down into the ear
canal.
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Sweet /or Viscid Pharmaceutical Solutions
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These include Syrups, Honeys, Mucilages, and
Jellies. All of these preparations are viscous
liquids or semisolids. The sweetness and viscid
appearance are given by sugars, polyols, or
polysaccharides (gums). SYRUPS Syrups are
concentrated solutions of sugar such as sucrose
in water or other aqueous liquid. simple syrup
when water is used alone for making syrup.
medicated syrup when the aqueous preparation
contains some
added medicinal substance flavored syrup which
contains aromatic or pleasantly
flavored substances and is intended to
be used as a vehicle
or flavor for prescriptions
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• Polyols (e.g. glycerin or sorbitol) may be added
  to
• - retard crystallization of sucrose or
• - increase the solubility of added ingredients.
• Alcohol often is included as
• - preservative
• - solvent for volatile oils.
• Syrups possess remarkable masking properties for
  bitter and saline drugs.
• It is important that the concentration of sucrose
  approaches but not quite reach the saturation
  point, WHY?
• In dilute solutions sucrose provides an excellent
  nutrient for molds, yeasts, and other
  microorganisms.
• In concentration of 65 by weight or more the
  solution will retard the growth of such
  microorganisms (WHY?).
• A saturated solution may lead to crystallization
  of a part of the sucrose under conditions of
  changing temperature.

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When heat is used in the preparation of syrups,
there is almost certain to be an inversion of a
slight portion of the sucrose. C12H22O11
2 C6H12O6 Sucrose heat acid Invert sugar
(dextrose and levulose) The speed of
inversion is greatly increased by acids (why ?)
the hydrogen ion acts as a catalyst in this
hydrolytic reaction. Invert sugar ? is more
readily fermentable than sucrose ? tend to darken
in color ? retard the oxidation of other
substances. The levulose formed during inversion
is sweeter than sucrose therefore the resulting
syrup is sweeter than the original syrup. When
syrup is overheated it caramelizes.
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• Invert Syrup
• It is prepared by hydrolyzing sucrose with
  hydrochloric acid and neutralizing the solution
  with Ca or Na carbonate.
• The sucrose in the 66.7 w/w solution must be at
  least 95 inverted.
• The invert syrup, when mixed in suitable
  proportions with syrup, prevents the deposition
  of crystals of sucrose under most conditions of
  storage.

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• Preparation of Simple Syrup
• (a) Solution with heat
• This is the usual method of making syrups
• in the absence of volatile agents or those
  injured by heat
• when it is desirable to make the syrup rapidly.
• The sucrose is added to the purified water or
  aqueous solution and heated until dissolved, then
  strained and sufficient purified water added to
  make the desired weight or volume.
• Excessive heating in the preparation of syrups
  must be avoided to prevent inversion of sucrose,
  with increased tendency to fermentation. Syrups
  cannot be sterilized by autoclaving without
  caramelization (yellow color).
• The specific gravity of syrup is an important
  property to identify its concentration. Syrup has
  a specific gravity of about 1.313, which means
  that each 100 ml of syrup weighs 1313 g.

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• (b) Agitation without Heat
• This process is used in those cases where heat
  would cause loss of valuable volatile
  constituents.
• The syrup is prepared by adding sucrose to the
  aqueous solution in a bottle of about twice the
  size required for the syrup. This permits active
  agitation and rapid solution.
• The stoppering of the bottle is important, as it
  prevents contamination and loss during the
  process.

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• (c) Addition of a Medicating Liquid to syrup
• This method is resorted to in those cases in
  which fluid extracts, tinctures, or other liquids
  are added to syrup to medicate it.
• Syrups made in this way usually develop
  precipitates since alcohol is often an ingredient
  of the liquids thus used and the resinous and
  oily substances dissolved by the alcohol
  precipitate when mixed with syrup.
• A modification of this process consists of mixing
  the fluid extract or tincture with the water,
  allowing the mixture to stand to permit the
  separation of insoluble constituents, filtering
  and then dissolving the sucrose in the filtrate.
• ?This procedure is not permissible when the
  precipitated
• ingredients are the valuable medicinal
  agents.

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• (d) Percolation
• In this procedure, purified water or an aqueous
  solution is permitted to pass slowly through a
  bed of crystalline sucrose, thus dissolving it
  and forming a syrup a pledget of cotton is placed
  in the neck of the percolator
• If necessary, a portion of the liquid is repassed
  through the percolator to dissolve all of the
  sucrose.
• This method is used for the preparation of Syrup
  USP.

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• Preservation of Syrups
• The USP suggests that syrups be kept at a
  temperature not above 25C.
• Preservatives such as glycerin, methyl paraben,
  benzoic acid and sodium benzoate may be added to
  prevent bacterial and mold growth, particularly
  when the concentration of sucrose in the syrup is
  low.
• The concentration of preservative is proportional
  to the free water.
• The official syrups should be preserved in well
  dried bottles and stored in a cool dark place.

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• Dextrose-Based Syrups
• Dextrose may be used as a substitute for sucrose
  (WHEN?) in syrups containing strong acids in
  order to eliminate the discoloration associated
  with inversion.
• Dextrose forms a saturated solution in water at
  70 w/v, which is less viscous than simple syrup.
  
• It dissolves more slowly than sucrose and is less
  sweet Preservatives are required to improve the
  keeping qualities of such syrups. Glycerin is
  added in 30 to 45 v/v as preservative.

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• Artificial Syrups (Non-Nutritive Syrups)
• intended as substitutes for syrups and are to be
  administered to persons who must regulate their
  sugar and/or calorie intake accurately. e.g.
  persons suffering from diabetes mellitus.
• Some early formulae included glycerin, however,
  glycerin and propylene glycol are glycogenetic
  substances, i.e. they are materials which are
  converted into glucose in the body.
• An example of nonnutritive syrup is Diabetic
  Simple Syrup. It contains compound sodium
  cyclamate (6 cyclamate sodium and 0.6 saccharin
  sodium)
• However, the cyclamate studies showed that the
  sweetener could produce cancer in animals and, as
  a result, this substance was removed from a wide
  variety of products. Similar studies have been
  carried out on saccharin. Much research has been
  done to find a safe synthetic substitute for
  sucrose. As a result, aspartame which is about
  200 times sweeter than sucrose, is being used now
  in many commercial preparations as the sweetening
  agent.

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• Sorbitol-Based Syrups
• Sorbitol which is hexahydric alcohol made by
  hydrogenation of glucose has been used in the
  preparation of syrup.
• It is used mostly in the form of a 70 w/w
  aqueous solution.
• Sorbitol solution is not irritating to the
  membrane of the mouth and throat and does not
  contribute to the formation of dental carries.
• Sorbitol is metabolized and converted to glucose
  however, it is not rapidly absorbed from the GlT
  as sugars. No significant hyperglycemia has been
  found (WHY?) it may be used as component of
  non-nutritive vehicles.
• Sorbitol solution does not support mold growth.
  Preservative should be used in solution
  containing less than 60 w/w sorbitol.
• It is chemically stable and inert with respect to
  drugs and other ingredients used in
  pharmaceutical perpetration.

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Sorbitol
Glucose
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• HONEYS
• Are thick liquid preparations. At one time,
  before sugar was available, honey was used as a
  base, instead of syrup.
• There are few official preparations containing
  honey. e.g. Oxymel, or" acid honey "'is a mixture
  of acetic acid, water and honey
• MUCILAGES
• The official mucilages are thick viscid, adhesive
  liquids, produced by dispersing gum (acacia or
  tragacanth) in water.
• Mucilages are used as suspending agents for
  insoluble substances in liquids their colloidal
  character and viscosity prevent immediate
  sedimentation.
• Synthetic agents e.g. carboxymethylcellulose
  (CMC) or polyvinyl alcohol are nonglycogenetic
  and may be used for diabetic patients.

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• Jellys
• Preparations having a jelly-like consistency.
  They are prepared also from gums.
• Are used as lubricants for surgical gloves and
  catheters
• Lidocaine HCl Jelly USP is used as a topical
  anaethetic.

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Non-Aqueous Pharmaceutical Solutions
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• Advantages
• If the drug is not completely soluble or unstable
  in aqueous medium it may be necessary to use an
  alternative non-aqueous solvent.
• Oily solutions of drugs are often used for depot
  therapy e.g. in muscles
• It is essential to test
• toxicity irritancy flammability cost
  stability and compatibility of solvents to avoid
  problems
• Solvents such as acetone, benzene and petroleum
  ether are not used for internal products.
• Internal products may contain ethanol, glycerol,
  propylene glycol certain oils.
• For parental products the choice is very limited

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This section is devoted to four groups of
non-aqueous solutions 1. alcoholic or
hydroalcoholic solutions, e.g. elixirs and
spirits, 2. ethereal solutions, e.g. the
collodions 3. glycerin solutions, e.g. the
glycerites, 4. oleaginous soIutions e.g. the
liniments, medicated oils, oleo- vitamins,
sprays, and toothache drops.
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• ELIXIRS
• Are clear, pleasantly flavored, sweetened
  hydroalcoholic liquids intended for oral use.
• They are used as flavors and vehicles e.g.
  Dexamethasone Elixir USP and Phenobarbital Elixir
  USP.
• The main ingredients in elixirs are ethanol and
  water but glycerin, sorbitol, propylene glycol,
  flavoring agents, preservatives, and syrups are
  often used in the preparation of the final
  product.
• EIixirs contain ethyl alcohol, however, the
  alcoholic content will vary greatly, from elixir
  containing only a small quantity to those that
  contain a considerable portion as a necessary aid
  to solubility
• An elixir may contain water and alcohol soluble
  ingredients.

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• Incompatibility of elixir
• Alcohol precipitates water soluble substances
  e.g. tragacanth, acacia agar and many inorganic
  salts from aqueous solutions.
• If an aqueous solution is added to an elixir, a
  partial precipitation of ingredients may occur.
  This is due to the reduced alcoholic content of
  the final preparation.

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• SPIRITS
• Alcoholic or hydroalcoholic solutions of volatile
  substances. The active ingredient may be gas,
  liquid or solid.
• Spirits may be used internally for their
  medicinal value, by inhalation but is mostly used
  as flavouring agents.
• Spirits should be stored in tight,
  light-resistant containers and in a cool place,
  WHY?
• Spirits are preparation of high alcoholic
  strength and when diluted with aqueous solutions
  or liquids of low alcoholic content turbidity may
  occur, WHY?

63

• COLLODIONS
• Are liquid preparations containing pyroxylin (a
  nitrocellulose) in a mixture of ethyl ether and
  ethanol.
• They are applied to the skin by means of a soft
  brush or other suitable applicator and, when the
  ether and ethanol have evaporated, leave a film
  of pyroxylin on the surface.
• The official medicated collodion, Salicylic Acid
  Collodion USP, contains 10 w/v of Salicylic
  Acid in Flexible Collodion USP and is used as a
  keratolytic agent in the treatment of corns and
  warts.
• Collodion is made flexible by the addition of
  castor oil and camphor.

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• GLYCERINS
• Glycerins or glycerites are solutions or mixtures
  of medicinal substances in not less than 50 by
  weight of glycerin.
• Most of the glycerins are extremely viscous.
• Glycerin is a valuable pharmaceutical solvent
  forming permanent and concentrated solutions not
  otherwise obtainable.
• Glycerin is used as the sole solvent for the
  preparation of Antipyrine and Benzocaine Otic
  Solution USP. As noted under Otic Solutions,
  glycerin alone is used to aid in the removal of
  cerumen.
• Glycerins are hygroscopic and should be stored
  in tightly closed containers.

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• LINIMENTS
• Are solutions or mixtures of various substances
  in oil, alcoholic solutions of soaps, or
  emulsions.
• They are intended for external application and
  should be so labeled.
• They are applied with rubbing to the affected
  area, the oil or soap base providing for ease of
  application and massage.
• Alcoholic liniments are used generally for their
  rubefaciant and counterirritant effects. Such
  liniments penetrate the skin more readily than do
  those with an oil base.
• The oily liniments are milder in their action and
  may function solely as protective coatings.
• Liniments should not be applied to skin that are
  bruised or broken.

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Rubefacient a substance for external application
that produces redness of the skin e.g. by causing
dilation of the capillaries and an increase in
blood circulation. Counterirritant a medicine
applied locally to produce superficial
inflammation in order to reduce deeper
inflammation
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• OLEO VITAMINS
• Oleo vitamins are fish liver oils diluted with
  edible vegetable oil or solutions of the
  indicated vitamins (usually vitamins A and D).
• The indicated vitamins are unstable in the
  presence of rancid oils and, therefore, those
  preparations, should be stored in small, tight
  containers, preferably under vacuum or under an
  atmosphere of an inert gas, protected from light.