Coating drug solubility

FMC designs one such water-soluble coating for timed-release medications — Aquacoat ECD, a 30% by weight aqueous dispersion of ethylcellulose. This polymer is used to coat drug-layered beads that are delivered using gelatin capsules... 

Ragnarsson, G., Sandberg, A., Johansson, M. O., Lindstedt, B., and Sjogren, JJi(i K998)release characteristics of a membrane-coated pellet formulation-m uence of drug solubility and particlelsize,... 

When drug solubility is very high or drug loading is below the drug solubility, Equation (6.131) is applied to the perforated, coated tablets. Due to the diffusion term in Equation (6.131), the drug release kinetics are linear for the perforated, coated tablets. Figure 6.36 shows the release of diltiazem HC1 from the perforated, coated tablets. 

Urea Urea has been used both to form solid dispersions by the cooling of urea-drug mixtures and to directly coat drug-laden particles in melt-coating operations. It has a melting point of approximately 130°C and is highly soluble in water. A variety of urea-drug dispersions obtained from melt processes... 

Fumaric acid has been investigated as a lubricant for effervescent tablets and copolymers of fumaric acid and sebacic acid have been investigated as bioadhesive micro-spheres. " It has been used in film-coated pellet formulations as an acidifying agent and also to increase drug solubility. ... 

No basal acid secretion in the stomach during fasted state, and thereby often close to neutral pH in contrast to the acidic human pH. However, an acidic pH may be induced in some individuals without intake of food. This has to be specially considered, for example, when drug solubility is pH dependent and for enteric-coated formulations, for which drug release is dependent on the pH in the GI tract. 

Important properties of coatings include solubility/insolubility in physiological fluids, drug diffusibility through water-insoluble films, water vapour and oxygen permeability, and thermal, mechanical and adhesive characteristics. These characteristics can be evaluated either directly on isolated films or indirectly after deposition on the considered dosage forms. 

A number of the water-soluble polymers also have adhesive properties which are being extensively evaluated for drug delivery (9). These polymers will adhere to the mucous coating in the gastrointestinal tract, the nose, and the mouth to delay passage and sustain drug release. Those polymers with the best adhesive properties are those with hydroxyl and carboxyl groups. Table II lists some of the bioadhesive polymers and their adhesive properties. 

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... 

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