WURSTER COATING- PROCESS AND PRODUCT VARIABLES - IJPI

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INTERNATIONAL JOURNAL OFREVIEW ARTICLEPHARMACEUTICAL INNOVATIONS ISSN 2249-1031selection of nozzle, smaller the nozzleinsert, more consistent will be spray.However smaller nozzle insert may causenozzle choking. To avoid agglomeration inwurster coater the coating fluid is to beatomized more finely than in pan coaterfor tablets. It is necessary that the nozzleused in capable of atomising the coatingfluid even if the coating fluid delivery rateis increased. Large droplets of coatingfluid generated by low performance nozzledoes not distribute evenly over the materialto be coated and do not dry quickly assmaller droplets. Very small droplets maydry quickly. Some droplets may contacttablets or beads surface but may dry beforegetting spread, it will result in to theirregular surface on core material. Tomaintain uniform atomisation when sprayrate exceeds the capacity of nozzle largedroplets of coating fluid appears alongwith small droplets, large droplets resultsin to the formation of agglomerates. Toavoid agglomeration multiple unit nozzlesshould be used. [1,8, 10,11] .Atomisation Air: If the atomisationpressure is high then the mist size will belower, then the chances of agglomerationwill also low. Excess pressure will lead toa particle shooting to the filter bag. Theatomisation pressure varies from 2 bar to 4bar. This will depend upon the kind ofbinder used its evaporation rate and itsviscosity. If in the finished granulationlumps of binder is present, then that wouldmean the air pressure has been lower thanrequired. The atomisation air must beadjusted to keep enough to avoidagglomeration. During the optimisation ofspray rate to achieve fastest possibleprocess, one has to keep droplet veryVolume 2, Issue 2, March− April 2012small. Higher the pressure smaller will bedroplet [2, 5, 7] .Product variablesCore particle: In some cases the coreparticles are used, it can be drug core itselflike spherodised and extruded product orpellets of inert material used to load drug.Controlled release of drug is mainlydependent upon the thickness of the filmon the pellets. If the specifications set forthe core is not rigid enough and if theaverage particle size of core varies, evenby 50 micron, this will lead toconsiderable change in the film thicknesswith same % coating.Particle surface: If the particle surfacewill rough the total coating area availablefor coating will change. The pellets withrough surface will have more surface areathen a pellet with smooth surface. To coveredges and crevices of rough pellets one hasto make film thicker but the total quantityapplied typically may exceeds theminimum required for acceptableperformance. And large pores may neverbe covered, resulting in an imperfection inthe film. Due to attrition during theprocess it is not easy to preserve the drugpellets as smooth as possible. In oneinstance, the product temperature in drugloading stage changed .when the producttemperature reduced from 60 to 35°C, onthe whole SR coating required to getdesired release was diminished from 21%to 12% even though all parameters in SRcoating kept same. This is mainly due tosmooth surface of the drug pellets whenprocessed at low temperature due toreduced spray drying and higher moisture.When the drug loading was done at highertemperature, the surface of drug loaded64 | P a g ehttp://www.ijpi.org
INTERNATIONAL JOURNAL OFREVIEW ARTICLEPHARMACEUTICAL INNOVATIONS ISSN 2249-1031pellets was rough and porous due to spraydrying effect. To cover these pores one hasto apply more coating.Particle size: As the particle sizedecreases the amount of coating materialrequire for desire thickness becomes veryhigh. The quantity of liquid also increasesas a result of decrease in particle sizebecause coating substance must be appliedusing some medium which is solidconcentrations in liquid in range of 10 to30%. Further complication is that as theparticle size decreases agglomerationbecomes more dependent on theformulation of the coating liquid andnozzle which is unavoidable. So itsuggested to use large particle size thatmay reasonably produce the desired results[6] .Product temperature: Specification ofproduct temperature will depend upon theglass transition temperature of polymer. Toget maximum efficiency it is we have tokeep product temperature as low aspossible. Lower the product temperaturelesser will be the static charge generationbut for some polymer like HPMC we haveto maintain high temperature to minimisethe agglomeration by drying the filmeffectively [1, 7] .Solution Viscosity and SolutionConcentration: We have to optimise theseparameters to have better control on theprocess. We have to reduce the spray rateif the solution is viscous and tacky. It isgenerally known that, higher solid contentwill reduce the process time. But it isopposite in case of polymers like HPMCand ethyl cellulose when they are insolution form. As we increase the solidcontent beyond certain limit for theseVolume 2, Issue 2, March− April 2012polymers, the spray rate will reduceradically, which results in higher processtime [2, 6] .Bulk Density of Finished Product: Onceit was thought it is uncontrollable propertybut research has shown that byconcentrating on two variables it can bereduced or altered. These factors are the inprocess moisture and the fluidizing airvolume. The lowest possible finishedproduct bulk density can be achieved bykeeping the bed moisture at or below themaximum finished product moistureduring spraying. In this way drying stage(which can cause product attrition andincreased bulk density) is not needed afterspraying. Volume of fluidizing air can beaffected by several factors. As the outer airfilter or the product bowl screen becomesoccluded by binder, by coating material, orby fine powders resistance to air flowincreases. Without a warning indicator thevolume of air can drop enough to cause thebed moisture to increase thereforeincreasing the bulk density of finishedproduct [1, 6] .References1. Jones David M. Factors to Consider inFluid Bed Processing. PharmaceuticalTechnology.April 1985.2. Dr. Mehta Atul M. Scale upConsiderations in the Fluid BedProcess for Controlled ReleaseProduct. Pharmaceutical Technology.Feb. 1988.3. Lachman Leon, Lieberman Herbert A.Kanig Joseph L.The Theory andPractice of Industrial Pharmacy. 3rd ed.Bombay: Varghese publishinghouse.1987:419 - 420.65 | P a g ehttp://www.ijpi.org
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WURSTER COATING- PROCESS AND PRODUCT VARIABLES - IJPI

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