Tablet formulation coating

Rowe RC, Woolgar CG. Neurofuzzy logic in tablet film coating formulation. Pharmaceut Sci Technol Today 1999 2 495-7. 

Rowe RC, Roberts RJ. The effect of some formulation variables on crack propagation in pigmented tablet film coatings using computer simulation. Int J Pharm 1992 86 49-58. 

Designed experimentation, involving mostly some type or modification of factorial design, has been used to study many different types of formulation problems. These include a pharmaceutical suspension [21], a controlled-release tablet formulation [22], and a tabletcoating operation [23]. In the latter case, Dincer and Ozdurmus studied an enteric film coating and utilized the steepest descent graphic method to select the optimum. 

Wu et al. [46] used the approach of an artificial neural network and applied it to drug release from osmotic pump tablets based on several coating parameters. Gabrielsson et al. [47] applied several different multivariate methods for both screening and optimization applied to the general topic of tablet formulation they included principal component analysis and... 

Zentner and coworkers [24,26] utilized this information in their development of a system that releases this drug over a 24 hr period. The use of NaCl to modulate the release of diltiazem presents an interesting problem in that the concentration of the solubility modifier must be maintained within certain limits and below its saturation solubility within the device. To solve this problem, core formulations were developed that contained both free and encapsulated NaCl. The encapsulated NaCl was prepared by placing a microporous coating of cellulose acetate butyrate containing 20 wt% sorbitol onto sieved NaCl crystals. The coated granules released NaCl over 12-14 hr period via an osmotic mechanism into either water or the core tablet formulation. The in vitro release profile for tablets (core I devices) containing 360 mg of diltiazem HC1 and 100 mg of NaCl equally divided between the immediate release and controlled release fractions... 

The U. S. Dispensatory26 reports maximum serum levels of 0.2 ijg./ml. 1 hour after administration of a 250 mg. dose, 0.6 (ig./ml. 2 hours after a 500 mg. dose, and 1.2 ug./ml. 2 hours after a 1 g. dose. Higher blood levels are achieved on a multiple dosage schedule. Since it is acid labile, a resistant coating is used in tablet formulations to overcome the deleterious effect of gastric fluid on erythromycin base or the stearate salt is prepared which does not dissolve readily in the stomach. 

Some key attributes of coated products and coating processes that may well be used to set objectives for optimizing a coating process are shown in Table 2. In many cases, the attributes as listed are very subjective, and thus must be defined in clearly measurable terms if they are to be used as the basis for process optimization. Additionally, meeting defined objectives may equally be dependent on the existence of certain coating and tablet formulation attributes. Nonetheless, while the information listed in Table 2 is not meant to be all-inclusive, it does provide an idea of the types of responses that could be used as a basis for optimizing a coating process. 

G. T. Greco, III. Segregation of active constituents from tablet formulations during grinding effects on coated tablet formulations, Drug Dev. Ind. Pharm., 11 1889 (1985). 

Enteric coating materials are also used to prevent release of the drug substance in the stomach if the drug is either an irritant to the gastric mucosa or unstable in gastric juice. Table 7 lists enteric coating polymers commonly used in tablet formulations. The choice of of enteric coating material depends on its solubility. 

TABLE 7 Enteric Coating Polymers Commonly Used in Tablet Formulations... 

Like many other herbal extracts, valerian extract is very hygroscopic. Inclusion into tablets raises stability issues. Coatings reduce moisture absorption but often lead to tablet explosion or visual deterioration (black specs). Tablets formulated with 250 mg valerian extract, spray-dried lactose, and compressible starch were... 

Plumb, A. P., Rowe, R. C., York, P., and Doherty, C. (2003), Effect of varying optimization parameters on optimization by guided evolutionary simulated anneahng (GESA) using a tablet film coat as an example formulation, Eur. J. Pharma. Sci., 18, 259-266. 

Mesalazine. Patients intolerant of salazopyrin usually tolerate mesalazine, which is 5-ASA. Mesalazine is absorbed rapidly and completely in the upper jejunum, and is presented in various formulations which delay its release. Asacol tablets are coated in a resin, which dissolves only at a pH of 7 or higher, favouring its release in the ileum and colon. In contrast Pentasa has a slow-release but pH independent coating so that 5-ASA is liberated throughout the gastrointestinal tract. 5-ASA that enters the blood is rapidly cleared by acetylation in the liver and renal excretion. In addition to oral formulations, mesalazine is available as an enema. 

Multiporous oral drug absorption system. A single-unit, immediate-release tablet formulation consisting of an inner core, containing active drug plus excipients, surrounded by a non-disintegrating, timed release coating. 

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