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Looking for past articles? Check out Tablets & Capsules article archive tabletscapsules.com (enter username & password or click register) Popular topics: Capsule & capsule filling Tablets & tableting Excipients Analytical techniques Dietary supplements Formulation Granulation c The advantages of inte drums for tablet coati coating erchangeable ng systems James Hahn Thomas Enginee ering R d R h R n R i R n R a R h R c R D R & R c R g d T f o t r f i n e n n o e This article gives examples of how using a coating system with interchangeable drums simplifies production increases, preserves capi al, and makes better use of floor space. D and pilot-scale coating systems have used inter- geable drums for more than 25 years, including a 24- diameter lab-scale system that my company intro- duced in 1990 [1]. en years ago, we extended the interchangeable-drum concept to production-scale equip- ment [2]. As a result, manufacturers of pharmaceuticals d a d d and nutraceut lab and use sim as large as 1,20 Whatever t coating drum advantages ove duction setting ties, meaning y the traditional (maximum-to-m able drums, the t t r icals can coat as few as 100 tablets in the milar equipment to coat production batches 00 liters (900 kilograms). their size, systems that use interchangeable s are widely accepted and provide many er systems that use fixed-sized d ums. In a pro- , the key benefit is the larger range of capaci- your coating operation is no longer limited to turndown ratios of 2-to-1, 3-to-1, or 4-to-1 minimum capacity). Rather, with interchange- e urndown ratios increase to 10-to-1 or bet- film coating model to better understand and prevent scuffing. Rosof and Sheen described the different classes of titanium diox- ide and the severity of their scratching a stainless steel coat- ing pan [1]. Ogasaware et al. attempted to link the quantity of titanium dioxide in the coating formula to the condition of the coating pan and the level of product fill (pan charge) [2]. They also noted that scuffing didn't seem to be specific to the type of coating formulation or to the type of poly- mer in the formulation. Nor did they observe scuffing in all coating pans, indicating that the surface finish of the pan may contribute to it. Whatever its source, scuffing has led some companies to adopt a traditional approach when applying white coatings: Coat the pan with the white coat- ing solution before loading the tablets into the pan. Coating constituents vary according to the need of the tablet and thus vary widely, and the FDA lists more than he term scuffing describes a defect of film-coated tablets in which dark spots or gray streaks appear on tablet faces when the cores are coated with a white or light-color formulation. This defect appears infrequently and intermittently, and is thus difficult to troubleshoot or to duplicate in a laboratory environment. Suppliers of aqueous coatings have examined the issue but have yet to explain fully why scuffing occurs. Nor has a root cause been identified. The work described here explored sev- eral ideas about the source of the defects, including 1) how the level of titanium dioxide in the coating formula contributes, 2) how the availability of free iron oxides on the surface of the coating pan contributes, and 3) how the frequency of pan passivation contributes to the prob- lem or to the understanding of it. Much conjecture, with some manufacturing observa- tions mixed in, has been offered to explain or apply a This article summarizes the results of a study to determine the cause or causes of scuffing, a defect of film-coated tablets in which dark spots or gray streaks appear on tablets coated with white or light colors. capsule coating Using a small-scale capsule dip coater to produce gastro- resistant hard capsules Rut Sun _ 1/4/08 3:45 PM Page 1 oating th Dodds and Fridrun Podczeck nderland University bsorbing properties of the gelatin shell make achiev- od film adhesion difficult [3]. In addition, the use of us film formulations causes the gelatin shells to and they become sticky as a result of gelatin solubi- n [4]. Furthermore, the drying that takes place dur- ray coating evaporates water from the shell, causing ecome brittle. Aqueous cellulose acetate trimellitate However The hard shell capsule is a modern means of drug delivery r, film coating of either the capsule content or the filled , film coating of either the capsule content or the filled capsule itself is required to delay drug release, for example, by an enteric film coating. This article describes how an enteric film coating can be applied to hard capsules on a small scale—for use in the hospital environment or clinical trials, for example— ns of drug delivery. content or the filled for example, by an how an enteric film a small scale—for rials, for example— ates alternative shell the coated capsules. ufacturing scale to 1]. Enteric-coated re produced with ple is Colpermin, udragit S100 and hard capsules with non-absorbing properties of the gelatin shell make achiev- ing good film adhesion difficult [3]. In addition, the use of aqueous film formulations causes the gelatin shells to soften and they become sticky as a result of gelatin solubi- lization [4]. Furthermore, the drying that takes place dur- ing spray coating evaporates water from the shell, causing it to become brittle. Aqueous cellulose acetate trimellitate coatings were found to provide poor gastro-resistance in general, and water penetrating the capsule shell during coating was problematic. The problem of water penetra- tion worsened according to the coating used in this order: poly(methacrylic acid, ethyl acrylate) 1:1, cellulose acetate phthalate, and cellulose acetate trimellitate [5]. A minimum coating level of approximately 8 milligrams per square centimeter (mg/cm 2 ) of copolymer of methacrylic acid and its methylester was reported for a brand of liquid- filled propranolol hard gelatin capsules [6]. H polymers, such as Eudragit. One example is Colpermin, H capsule dosage forms on the market are produced with H produce an enteric-coated dosage form [1]. Enteric-coated H ard capsules can be coated on a manufacturing scale to H Eudragit L30 D55. T p using a dip coating process. It also investigates alternative shell materials to gauge the long-term stability of the coated capsules. capsules can be coated on a manufacturing scale to p ce an enteric-coated dosage form [1]. Enteric-coated c e dosage forms on the market are produced with polymers, such as Eudragit. One example is Colpermin, which is coated with a mixture of Eudragit S100 and Treatment of filled hard capsules with reatment of filled hard capsules with formaldehyde-containing ethanolic solutions has also been suggested [2], but the authors of that study found that the filling had a clear influence on the coating prop- erties, and thus they suggested that—in the case of freely or very water soluble drugs—hydrophobic excipients should be added to the powder formulation to increase the hydrophobicity of the powder plug. Furthermore, residual formaldehyde could promote capsule shell hard- ening on storage [3] and, as a result, embrittlement or lack of drug release could render the product unusable. Studies of the film coating of hard capsules have usu- ally involved hard gelatin capsules, and the physical prop- erties of the gelatin film are important for film adhesion and product stability. In fact, the smooth, non-porous and or gastro-resistance in e capsule shell during lem of water penetra- ting used in this order: ylate) 1:1, cellulose tate trimellitate [5]. A ately 8 milligrams per olymer of methacrylic d for a brand of liquid- propranolol hard gelatin capsules [6]. In all of the above results, the polymers used as enteric coatings were applied to gelatin hard shell capsules using conventional industrial spray coating procedures. However, in the hospital environment or when preparing small samples for clinical trials, it is not possible to use such techniques due to lack of laboratory equipment to spray-coat 10 or 20 capsules. A dip coating process, how- ever, can be employed to coat capsules in batches as small as one capsule. The main drawback to dip coating is that it exposes the capsule shell to considerably more liq- uid than a spray coating process, which applies only a small amount of coating and continuously dries it. As a result, dip coating cannot be undertaken with aqueous suspensions of polymer.