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Introduction, • Biphasic liquid dosage forms contain two phases., • This includes undissolved drug snd the solvent system (vehicle). The, undissolved phase is distributed throughout a vehicle and intended for, oral administration., • In these preparations, the distributed phase is called ‘dispersed phase’, and the vehicle is called ‘dispersion medium’. They are also reffrred as, internal phase or continuous phase respectively.
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Need of biphasic liquid dosage form, • The need of biphasic liquid dosage form arise when the medicaments are poorly, soluble in the solvent system . Medicaments from the dispersed phase of the, system which might be either solid or liquid., • When solid medicament is distributed in the dispersion medium the system, formed is called ‘suspension’, but in case of liquid medicament, system formed is, called émulsion’., • These two highly unstable systems are made stable by employing various, pharmaceutical aids like; suspending agents in suspensions and emulsifying agents, in emulsions., • They are categorized as coarse dispersions since they contain coarse particles,, usually 1 to 100 microns in size. Dispersions containing particles of smaller size, are called fine dispersions and if the particle are in the colloidal range (< 1, micron), they are termed as Magmas.
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Suspensions, , “Suspension are referred as solid-liquid dispersions. They are, heterogeneous systems in which poorly, soluble drugs in finer particle, size are distributed in the vehicle”., “Suspension are heterogeneous, biphasic liquids dosage form in which, insoluble solid particulate (internal or dispersed phase) are uniformly, distributed in liquid phase (external phase or dispersion medium), which, may be stabilized by inclusion of suspending agents”.
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Advantages of suspensions, 1., , Certain drugs which are unstable in solution form a stable system when suspended., , 2., , They have all the advantages of oral liquid dosage forms over solid dosage forms. i.e. tablets, and capsules, , 3., , The disagreeable taste of certain drugs in solution form is negligible when they are given in their, suspension forms., , 4., , The taste of certain drugs is improved with regard to palatability if their solubility is reduced or, they are made insoluble or poorly soluble. In such case there is no way to administer those drugs, in the form of suspensions. Ex. Water insoluble ester form of chloramphenicol i.e., chloramphenicol palmitate , which was developed in order to prepare a palatable oral liquid, dosage form of chloramphenicol as a suspension of chloramphenicol palmitate oral suspension., , 5., , Mostly oral suspensions have aqueous vehicle which might be flavpured or sweetened to the, tatse of the patients.
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Disadvantages of suspensions, 1., 2., 3., 4., 5., 6., , They have all the disadvantages of liquid dosage forms, They require suspending agents to suspend the fine particles of dispered phase., The rate of dispersed phase can be reduced but can not be made zero. The settled, particles after a long period may turn to cake which cannot be re-dispersed even after, gentle shaking of the suspensions. Such suspensions are called lost suspensions., Most of the suspending agents are hydrocolloids which support the growth of micro, organisms in the preparation. thus, suitable preservatives are included in the, preparations., Some drugs are poorly wettable in nature, which might have not formed a homogenous, system if their wettability is not increased. Thus, proper wetting agents (surfactants) are, to be included into the preparation., They also require viscosity increasing agents to improve the stability of the preparation., Highly viscous systems might result in the poor release of the drug from the system.
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Ideal Properties of Suspensions., 1., 2., 3., 4., 5., , They should be pharmaceutically elegant., They should be physically and chemically stable., They should have good asthetic properties with regard to taste and color., Rate of sedimentation of dispersed phase should be slow., The sediment must be redispersed upon the gentle shaking of the, container., 6. The particle size of the dispersed phase must remain fairly constant, throughtout the shelf period of the preparation., 7. The flow of the suspension must be optimum so that it is readily and, evenly available from the container., 8. Suspension for parentral use must not loss its efficacy during sterilization.
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Classification, Based On Route of Application or Pharmaceutical use, • Oral suspension e.g. antacid, antibiotic, • Externally applied suspension e.g. lotion, • Parenteral suspension, • Ophthalmic suspension, Based On Proportion Of Solid Particles, • Dilute suspension (2 to 10% w/v solid), • Concentrated suspension (50% w/v solid), Based On Electrokinetic Nature Of Solid Particles, • Flocculated suspension, • Deflocculated suspension
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Based On Route of Application or Pharmaceutical use, • Oral suspension, • Parenteral suspension, • Ophthalmic suspension, • Externally applied suspension
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Oral suspension, • The suspensions are to be consumed by the patient by oral route. Oral, suspensions genrally contain flavouring agent and sweetening agent to, mask the bitter taste of the drug., • They are also made palatable by using a suitable derivatives of drugs, eg, chloramphenicol palmitate suspension is prepared to mask the, bitter taste of chloramphenicol., • Nowadays suspensions are available in market in dry powder form and, these are reconstituted by adding a specified quantity of freshly boiled, and cooled water before use. eg, antibiotics in suspension for, paediatric use.
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• Advantages:, 1. It is easy to swallow the suspended insoluble medicaments., 2. The insoluble derivatives in suspensions is more palatable than soluble, derivatives in solution., 3. The bulky insoluble powders, such as kaolin and chalk can be, administered in suspensions in order to act as adsorbents of toxins or to, reduce excess acidity in the gestrointestinal tract., Disadvantages:, 1. All suspensions are required to be shaken before measuring a dose., 2. The accuracy of dosage is less reliable as compared to solution., 3. The storage of suspension may lead to change in dispersed system,, especially when there is fluctuation in temperature.
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Parenteral suspensions, • The suspensions which are administered by parenteral route are called, parenteral suspensions. The supensions are required to fulfilled the, following qualitites., 1. The particle size of the drug should be such that it can be easily pass, through the needle of the syringe., 2. There should not be any crystal growth in the suspension during its, storage., 3. The concentration of solid particles in the suspension should be between, 0.5 to 30%., 4. The viscosity of the suspension should not interface with it flow through, the syringe needle., 5. The suspension should be sterilized.
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Ophthalmic suspensions, • These are not commonly used as compare to eyedrops., • These are prepared only in those cases when the drug is insoluble in the desired, solvent or instable in liquid form., • These suspensions must fulfill the following conditions:, 1. The particle size of the eye suspensions should be fine enough so that it should, be non irritating to the eye., 2. The suspension should be sterilized., 3. These suspension should be isotonic., 4. These should have desired viscosity., 5. The suspension should be packed in a suitable container so that it can be easily, instilled into the eye.
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Suspensions for External use, • These suspensions are meant for external use eg. Lotions, inhalations,, eardrops, etc., • These suspensions contain very small particles to avoid grittiness., • Lotion containing suspended particles evaporate when applied to the, skin leaving a light deposite of medicament on the surface. Lotions are, easier to apply and less messy than anyother semisolid external, preparation., • Calamine lotion is a suspension type preparation which is applied on, the skin to provide protective effect. Lotions which are meant for, application on broken or inflamed skin should be free from harmful, microorganisms.
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Formulation of Suspension, • Suspending agents, • Wetting agents, • Flocculating agents, • Thickeners, • Buffers and pH adjusting agents, • Osmotic agents, • Coloring agents, • Preservatives, • External liquid vehicle
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Suspending agents:, • Suspending agent are also known as hydrophilic colloids which form colloidal dispersion with Water and, increase the viscosity of the continuous phase., , • Suspending agent form film around particle and decrease interparticle attraction., • Most suspending agents perform two functions i.e. besides acting as a suspending agent they also imparts, viscosity to the solution., • Ex. : Methylcellulose, hydroxyethylcellulose, tragacanth, acacia etc., Wetting agents (Surfactants):, • They are added to disperse solids in continuous liquid phase., • Hydrophilic materials are easily wetted by water while hydrophobic materials resist wetting. However, hydrophobic materials are easily wetted by non-polar liquids., • The extent of wetting by water is dependent on the hydrophillicity of the materials.
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• If the material is more hydrophilic less difficulty in wetting by water., • Surfactants decrease the interfacial tension between drug particles and, liquid thus liquid is penetrated in the pores of drug particle displacing, air from them and thus ensures wetting., • Generally, we use non-ionic surfactants but ionic surfactants can also, be used depending upon certain conditions., • Ex.: Polysorbate 80, • Polysorbate 80 is most widely used due to its advantages like non, toxicity and non ionic property (stable in pH of medium).
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Flocculating agents:, , • Dispersion can be improved by adding a surfactant or protective colloid which acts as, flocculating agent., • The flocculating agent acts by reducing the surface tension and thereby improving the, dispersion of solids and minimize flocculation., , • Ex.: sodium lauryl sulphate (SLS), carbowaxes and electrolytes, tween, span., Thickeners:, • These are hydrophilic colloids which form colloidal dispersions with water and increase, the viscosity of continuous phase of suspension, so that the solid particles remain, suspended in it for a sufficient long time to measure a uniform accurate dose., • Ex.: Gum acacia, Tragacanth, Starch, Sodium alginate etc.
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Buffers and pH adjusting agents:, • They are added to stabilize the suspension to a desired pH range or resist any, change in pH when an acid or base is added., • To encounter stability problems all liquid formulation should be formulated to an, optimum pH., • Rheology, viscosity and other property are also dependent on the pH of the, system., • Generally pH of suspension preferably at 7.4-8.4., • Most commonly used buffers are salts of weak acids such as carbonates, citrates, etc.
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Osmotic agents:, • They are added to produce osmotic pressure comparable to biological fluids when, suspension is to be intended for ophthalmic or injectable preparation., • Ex.: mannitol, sorbitol, NaCl etc., Coloring agents:, • They are added to impart desired color to suspension and improve elegance., • Colors are obtained from natural or synthetic sources used as coloring agents., • Plant colors are most widely used for oral suspension., • The synthetic dyes should be used within range of( 0.0005 % to 0.001%), • Color aids in in formulation for the identification of the product and the color used, shouldbe acceptable by the particular country., • Ex.: Indigo carmine gives blue colour, amaranth gives red colour etc.
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Preservatives:, • Preservatives are added to prevent microbial growth., • Ex.: Benzoic acid (0.1% in concentration), Butyl paraben 0.006-0.05% in, oral suspension and 0.02-0.4% in topical formulation., External liquid vehicle:, • They are added to construct structure of the final suspension., • Sweetening agents:, • They are used for taste masking of bitter drug particles., • Ex.: glucose, mannose, Sorbitol, sodium saccharin etc., • Bulk sweeteners is used at concentration of 15-70 %
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• Humectants:, • It absorb moisture and prevent degradation of API by moisture., • Ex.: propylene glycol, glycerol., • Total quantity of humectants should be between 0-10 % w/w.
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Method of Preparation of Suspension, • Step1: Grind or levigate the insoluble materials with the help of mortar to a, smooth paste with adding a vehicle containing the wetting agent., • Step 2: All soluble ingredients are dissolved in same portion of the vehicle, and added to the above prepared smooth paste to get slurry., • Step 3: Then the slurry is transformed to a graduated cylinder and the, mortar is rinsed with successive portion of the vehicle., • Step 4: Decide whether the solids are suspended in a structured vehicle/, Flocculated/ Flocculated and then suspended than add the vehicle, containing the suspending agent (or) flocculating agent., • Step 5: Make up the dispersion to the final volume via adding the external, liquid vehicle. Thus suspension is prepared.
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Method of Dispensing Suspensions (types), 1., 2., 3., 4., , Suspensions containing diffusible solids, Suspensions containing indiffusible solids, Suspensions containing precipitate forming liquids, Suspensions produced by chemical reaction
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Suspensions containing diffusible solids, • There are certain insoluble powdered substances are light in weight, and readily mixed in water and remain suspended throughout the, liquid for sufficient long time after shaking, Such substances are know, as diffusible solids., • Ex. Calcium carbonate, light magnesium carbonate, magnesium, trisilicate, rhubarb powder and light kaolin.
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• Genral method of dispensing:, 1. Care fully tare the container., 2. Finely powdered the solid ingredients, 3. Mix the insoluble powders in a mortar and add enough vehicle to make a smooth, cream., 4. Add more of vehicle to make it pourable., 5. Examine the suspension carefully and if it contains foreign particles, strain through a, muslin cloth into a tared container., 6. Rinse the mortar and pestle with successive volume of vehicle until they are quite, clean. Transfer the rinsing to the bottle., 7. Add any liquid ingredient., 8. Add more of vehicle to produce the required volume and mix thoroughly by shaking, the bottle.
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• Ex. Prepare and dispense the following suspension., Rx, light kaolin, 12 g, light magnesium carbonate 3 g, sodium bicarbonate, 3g, peppermint water add up to 90 ml, make a mixture, Direction: one dose to be taken 3 times a day.
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• Method:, • Mix the weighed quantities of light kaolin, light magnesium carbonate,, sodium bicarbonate in a mortar., • Measure out 3/4th of the peppermint water. Out of these add a small, amount of powder and and triturate thoroughly until a smooth paste is, formed then dilute it with remaining amount of peppermint water,, strain through muslin piece. Add more of peppermint water to produce, the require volume., • Transfer the suspension to a bottle, label and dispense.
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Suspensions containing indiffusible solids, • Indiffusible solids are those substances which do not dissolve in water, and do not remain evenly distributed in the vehicle for sufficient long, time to ensure uniformity of dose., • Ex., Used Externally, , Use Internally, , calamine, , Aspirin, , Hydrocortisone, , Aromatic chalk powder, , Sulphur precipitated, , chalk, , Zinc oxide, , phenobarbitone
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• Genral method of dispensing: (using compound tragacanth powder), 1. Finely powdered all the ingredients, 2. Mix them together in a mortar and add compound tragacanth powder, 3. Measure 3/4th of the vehicle and triturate to form a smooth cream, 4. Examine the suspension carefully and if it contains foreign particles,, strain through a muslin cloth into a tared container., 5. Rinse the mortar and pestle with successive volume of vehicle until they, are quite clean. Transfer the rinsing to the bottle., 6. Add any liquid ingredient., 7. Add more of vehicle to produce the required volume and mix thoroughly, by shaking the bottle
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• Ex., Rx, Bismuth carbonate, 1g, Prepared chalk, 1g, Kaolin, 4g, Tincture catechu, 2 ml, Water up to, 30 ml, Prepare a mixture. Send 4 dose, Direction: one dose to be taken 3 times a day.
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• Method:, • Mix the weighed quantities of bismuth carbonate, prepared chalk and, kaolin. To these incorporate calculated quantity of compound tragacanth, powder and mix thoroughly., • Measure out 3/4th of the peppermint water. Add a small amount of water and, triturate to form a smooth cream. Add the remaining portion of water., • Add remaining amount of water, strain through muslin piece. Add tincture, catachu in the centre of cream with continous trituration. Add more of water, to produce the require volume., • Transfer the suspension to a bottle, label and dispense.
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Suspensions containing precipitate forming, liquids, • There are certain liquid preparations that is precipitated on addition to, water. For ex. Compound benzoin tincture, myrrh tincture and tolu tincture., • These precipitates might be diffusible or indiffusible in nature. If the, pecipitates are diffusible in nature no need to add suspending agent., • These liquids are not insoluble in water but they form indiffusible, precipitates particularly when salts are present., • They contain resinous matter and when it is mixed with water, it leads to, precipitation of resin and may stick to the sides of the bottle which will be, difficult to rediffuse by shaking. To prevent this, a protective colloid is, dispersed in the vehicle before tincture is added.t, • Tragacanth mucilage (1/4th of the total volume) or compound tragacanth, powder (CTP) (2 g/100 ml) is commonly used as protective colloid.
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• General method of dispensing (using compound tragacanth powder), 1. Finely powderedsolid mixed with CTP., 2. Triturate the mixture with enough quantity of vehicle to form a cream., 3. Dilute the cream with small portions of vehicle with constant stirring to produce, about 50% of the final volume., 4. Measure a precipitate forming liquid in a dry measure and pour in a slow stream, into the centre of the suspension, stir rapidly. The resin particles are precipitated, the hydrocolloids (acasia, tragacanth) are absorbed over their surface conferring, hydrophilic properties and preventing aggregation into clots., 5. If the preparation contains and electrolyte, it must be added to the mixture,, keeping following precautions in mind:, 1. Do not add until resins have been protected, 2. Add in diluted form. Use half of the remaining water., 3. Add slowly with constant sterring to avoid local high concentrations, that might nutralize the effect of the protective colloid., 6. Finally, mixture is strained, if necessary make up the volume and mix.
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Method when Tragacanth Mucilage is used:, 1. Tragacanth mucilage is diluted with equal volume of vehicle in a beaker., 2. Measure, precipitate-forming liquid in a dry measure and pour in the, centre of the mucilage with constant sterring., 3. If the preparation contains an electrolyte. it must be added to the mixture,, keeping following precautions in mind:, 1. Do not add until resins have been protected, 2. Add in diluted form. Use half of the remaining water., 3.Add slowly with constant sterring to avoid local high, concentrations that might nutralize the effect of the protective, colloid., 4. Finally, mixture is strained, if necessary make up the volume and, mix.
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• Ex., Rx, Mixture of Lobelia Stramonium, Potassium Iodide, 2g, Ethereal tincture of Lobelia 8 ml, Tincture Stramonium, 16 ml, Chloroform water, 180 ml, Comments:, • This mixture contains contains tincture of lobelia as a precipitate-forming, liquid. Hence, particles of precipitate must be protected by using, hydrocolloid, like, either tragacanth powder or its mucilage, to prevent the, particles aggregation into clots., • This mixture is used in the treatment of asthama since lobeline and, hyoscyarnine (active ingredients of tincture of lobelia and stramonium, respectively) dilate the brochilo, relieve bronchial spasm and diminish the, secretion of mucus., • Chloroform water is a preservative vehicle.
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Suspensions produced by chemical reaction, • Sometimes insoluble precipitates are prepared in situ. Precipitates, obtained by chemical reactions are finer in nature if dilute solutions of, reactants are mixed. Thus, all the reactants are dissolved separately in, the vehicle and the two parts mixed. Precipitates found in this manner, are fine and diffusible and no suspending agents is required.
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Rx, , Sulphide Lotion BPC (white Lotion), Zinc sulphate, 40 g, Sulphurated potash 40 g, Purified water to, 1000 ml, Comments:, • 4% of each zinc sulphate and sulphurated potash is dissolved, separately in purified water and adding the solution of sulphurated, potash to the solution of Zinc sulphate slowly with constant stirring. A, reaction takes place and zinc sulphide is produced.
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• The addition of the sulphurated potash solution to that of the zinc sulphate is, necessary, rather than the reverse in order to obtain a finely divided precipitate., The slow addition and constant stirring contribute to the fineness of the, precipitate., • Precipitate of potassium sulphide usually cakes on standing and cannot be, redispersed evenly in the system on shaking. Thus, this lotion should be freshly, prepared to ensure uniformity. It should be shaken thoroughly before use, externally., • It is used in the treatment of acne and other skin conditions which can be trated by, antiseptic activity of sulphur., • Method:, • Dissolve the two ingredients separately in 400 ml of vehicle. Add sulphurated, potash solution slowly to the zinc sulphate solution with constant stirring. Transfer, to a tared container and make up the volume by purified water.
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Dispersions of oils ininhalations, • Volatile oils like eucalyptus and pumilio pine oils can uniformly be, distributed in aqueous system with the help of some diffusible adsorbents, like light magnesium carbonate., • The oils are triturated with adsorbent which allows the volatile oils in the, fine globules to get adsorbed., • When such dispersion (inhalation) is added to hot water, a free vaporization, of volatile oil take place., • If the quantity of adsorbent is not mentioned in the formula, following, quantites must be used:, 1. 1 g of Light magnesium carbonate for each 2ml of oil, 2. 2 g of Light magnessium carbonate for each 2g of volatile solid (e.g. menthol,, thymol etc)
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• Rx5, , Eucalyptus oil Inhalation, Eucalyptus oil, menthol, Light magnesium carbonate, Purified water to, , 5 ml, 1.5 g, 3.25g, 50 ml
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Comments:, • Eucalyptus oil is a volatile oil and menthol is a volatile substance., • In inhalationpreparation both must be adsorbed in their fine globules/particles on, to a good adsorbing agent., • Light magnesium carbonate is included for this purpose., Method:, • Finely powder the menthol in a glass mortar, add oil, stir until the solid is, dissolved., • Add light magnesium carbonate in small amount and mix well., • Vehicle is added in small portions to make a paste or cream., • Transfer to a tared container. Rinse the mortar with water and add rinsings to the, tared container. Finally, make up the volume.
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Suspensions ontaining poorly wettable solids, • Some solids like sulphur and hydrocortisone are insoluble in water as, well as poorly wetted by it. Poor wetting of the solid particles is due to, the high interfacial tension between solid liquid interface. Thus, to, ensure good dispersion of such types of solids, there must be reduction, in the interfacial tension which can be achieved by the addition of, enough quantity of surface acting agents., • Examples of wetting agents(surfactants) are soaps; like sodium lauryl, sulphate for external preparations and non ionic surfactants; like, polysorbates for oral and parenteral suspensions
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Comments:, • Precipitated sulphur is water insoluble as well as poorly wetted by it. Thus,, to improve its wettability it must be mixed with some surfactants (Sodium, lauryl sulphate), • Glycerin is added to provide soothing feeling and alcohol gets evaporated, on application, provides cooling sensation. Rose water is perfumed vehicle., Method:, • Participitated sulphur, glycerin, sodium lauryl sulphate and alcohol are, triturated to make a paste. Add rose water in portions with constant stirring, so as to make up the desired volume.
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Evaluation of Suspensions to ensure their, stability, • Sedimentation method., • Rheological method., • Electro kinetic method.
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• Sedimentation method :, • Two parameters are studied for determination of sedimentation., 1. Sedimentation volume., 2. Degree of flocculation.
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• Sedimentation volume, • The suspension formulation(50mL)was poured separately into100mL, measuring cylinders and sedimentation volume was read after 1,2,3 and, 7days,and there after at weekly intervals for 12 weeks., • Triplicate results were obtained for each formulation., • Sedimentation volume was calculated according to the equation:, • Where, F =sedimentation volume ,, • Vu = ultimate height of sediment, • Vo= initial height of total suspension.
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• Degree of flocculation (β), • It is the ratio of the sedimentation volume of the flocculated, suspension ,F , to the sedimentation volume of the deflocculated, suspension, F∞, • ß = F / F∞, • The minimum value of ß is 1,when flocculated suspension, sedimentation volume is equal to the sedimentation volume of, deflocculated suspension.
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•, •, •, •, •, , •, •, •, •, , Rheological method (Viscosity), It provide information about Settling behaviours., Brookfield viscometer is used to study the viscosity of the suspension, It is mounted on heli path stand and using T-bar spindle., T-bar spindle is made to descend slowly into the suspension and the dial reading on the, viscometer is then a measure of the resistance the spindle meets at various level., This technique also indicates at which level of the suspension the structure is greater, owing to particle agglomeration., The dial reading is plotted against the number of turns of the spindle., The better suspension show a lesser rate of increase of dial reading with spindle turns,, i.e. the curve is horizontal for long period.
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• ELECTROKINETIC, • Measurement of Zeta-potential using Micro electrophoresis apparatus, & Zeta Plus (Brook haven Instruments Corporation , USA), • It shows the stability of a disperse system.
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• The zeta potential of the formulated suspensions was determined using, a Zeta Plus.(Brook haven Instruments Corporation ,USA)., • Approximately 1mL of suspension was transferred into a plastic, cuvette using a pipette and diluted with distilled water., • The Brookhaven zeta potential software was used for the, measurement., • Parameters set to a temperature of 250C and refractive index(1.33)., • The zeta potential of the formulations was determined on day 0,7,, 14,21and day 28 post formulation.
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Stability problem, (a) Small particle size• Reduse the size of the dispersed particle increases the total surface, area of the solid. The greater the degree of subdivision of a given solid, the larger the surface area. The increase in surface area means also an, increase in interface between the solids and liquids leading to an, increase in viscosity of a system.
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• b) Increasing the viscosity – increasing the viscosity of the continuous, phase can lead to the stability of suspensions. This is so because the, rate of sedimentation can be reduced by increase in viscosity. Viscosity, increase is brought about by addition of thickening agents to the, external phase. In water these must be either soluble or swell. It is, important to note that the rate of release of a drug from a suspension is, also dependent on viscosity. Of a product. The more viscous the, preparation, the slower is likely to be the release of a drug. Sometimes, this property may be desirable for depot preparations.
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• C) TEMPERATURE., • Another factor which negatively affects the stability and usefulness of, pharmaceutical suspensions is fluctuation of temperature. Temperature, fluctuations can lead to caking and claying.
