Polymers enteric coated

Attempts have been made to achieve colon-specific delivery of drugs. These include 1) prodrugs and 2) polymers (enteric coated, those that are sensitive to degradation by bacterial enzymes, and matrices and hydrogels susceptible to degradation by bacterial enzymes). 

Chitosan would not seem suitable as a pH-sensitive polymer because it is soluble at acidic pH values, and becomes insoluble approximately at pH 6.5. Nevertheless, an enteric coating can protect chitosan from the acidity of the stomach. When the preparation reaches the intestine, the en-... 

Duloxetine hydrochloride, a novel anti-depressive, is known to be acid labile and, consequently, it has been formulated as an enteric-coated tablet. Interestingly, Jansen et al. [97] subsequently found that the drug was destabilised by degradation products within these enteric polymers. The authors found that succinyl and phthalyl residues from the hydroxypropyl methylcellulose acetate succinate (HPMCAS) and hydroxypropyl methylcellulose phthalate (HPMCP) formed... 

George A, Agyilirah GA, Banker GS. Polymers for enteric coating applications. In Tarcha PJ, ed. Polymers for Controlled Drug Delivery. Boca Raton, Florida CRC Press, 1991. 

Figure 5.2 Schematic representation of polymer dissolution and drug release from enteric-coated tablets.

At a pH lower than the pKa of an enteric coating polymer, [HP] Til, is equal to the intrinsic solubility of the nonionized polymer [HP]0. This solubility is often very low for enteric coating polymers, and thus dissolution of the coating layer at a low pH is very slow. At a pH higher than the pKa of the polymer, [HP]T/) is given by... 

Shellac.2 This is a naturally occurring polymer obtained from a gummy exudation produced by female insects. The pH at which drug is released is about 7, which may well be too high for most enteric-coated products. It is not recommended for developing a new product. 

Another example of an amine reacting with a formulation component is found in the case of duloxetine hydrochloride (84). This example, which is also discussed in Chapter 2, is summarized in Figures 49 and 50. In this example, the secondary amine of duloxetine hydrochloride reacted with the enteric coating polymer hydroxypropyl methylcellulose acetate succinate (HPMCAS) to form a succinamide degradation product. This reaction occurred under both stress conditions (60°C for 14 days) and during formal stability studies (30°C/60% relative humidity and 40°C/75% relative... 

Riedel and Leopold [35] investigated the degradation of omeprazole in organic polymer solutions and aqueous dispersions of enteric-coating polymers by UV spectroscopy. Data were compared with those obtained in a previous high-performance liquid chromatographic (HPLC) study. For comparative purposes the cationic Eudragit RS 100 and the monomeric acid acetic acid were included in this study. The discolorations of... 

Shellac is the oldest known material that has been used as enteric coating material. However, as a natural material, it lacks a crucial quality criterion of more modern polymers (i.e., batch-to-batch reproducibility). Hence, the most commonly used polymers today are the synthetic methacrylate copolymers or semisynthetic derivatives of cellulose. The main structural element of these polymers is an acidic function (either phthalate or methacrylic acid), which is responsible for the pH-dependent dissolution. 

A survey of the German market showed that more than 50% of enteric formulations were coated with methacrylate copolymers, about 40% with cellulose derivatives, 5% with shellac, and 3% with other materials [1], Enteric coating materials (Table 1) are described in various publications [21, 22], In addition to polymers mentioned in Table 1, others are being studied (e.g., to obtain release at lower pH) [23], Polymers with a dissolution at lower pH are intended for the protection of drugs in acidic medium and not for the protection of the gastric mucosa. 

The enteric protection properties of a methacrylate polymer were investigated with the use of naproxen tablets [56] enteric coated with an aqueous dispersion of methacrylic acid copolymer (EUDRAGIT L 30 D-55, USP NF type C). 

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