Polymer drugs water-soluble

Water-soluble polymers. Substituted water-soluble poly-orthoesters can be regarded as polysaccharide analogs, and could have potential medical applications as drugs or as drug carriers. Ionic substituents were introduced In the blcycllc monomers to Improve the solubility of these polymers. 

With recent advancement in polymer science, there has been the innovation of some novel drug delivery systems using polymers. Either the polymers used for pharmaceutical application are obtained from natural resources, which may be chemically modified for various applications, or some are synthesized chemically for use. A large number of natural and synthetic polymers are water soluble. Water-soluble polymers for pharmaceutical application are synthetic and natural. 

Because a number of contraceptive steroids, and particularly levonorgestrel, have water solubilities of only a few parts per million, the effect of drug water solubility on rate of release from bioerodible polymers into an aqueous medium becomes an important consideration and can, in fact, become rate limiting. 

Keywords Cydodextrins complexation, ternary cyclodextrin complexes, lipophilic drugs, water-soluble polymers... 

Because swelling and consequent bulk erosion induced by the water-soluble salt is not desirable, use of the low-water-solubility, sUghtly acidic salt calcium lactate was investigated (30). By using this excipient it was hoped that a lowering of the pH within the surface layers of the device would take place and release of the drug would be controlled by polymer erosion confined to the surface layers of the device. In these experiments norethindrone was replaced by the currently favored steroid levonorgestrel. 

This is illustrated in Scheme VI. The protected glyceryl derivatives are insoluble in aqueous media and appear to be hydrolytically stable. The deprotected species (structure 27) is water-soluble and hydrolyzes in aqueous media at neutral pH at 37°C to give glycerol, phosphate, and ammonia. The free hydroxyl units of the deprotected polymer provide sites for the covalent attachment of drug molecules. Water insolubility can be imparted by the use of appropriate hydro-phobic cosubstituent groups to generate solid, erodible materials. 

There are many polymers which have been used as physical matrices for controlled delivery of drugs. In this paper, these polymers are separated into water-soluble, biodegradable, and nonbiodegradable materials. A description of each class of polymers is presented. Examples of polymers from each class that have been used as drug delivery matrices and the criteria for their selection are included in this general review. 

Water-soluble polymers can also be used as aqueous solutions for drug delivery. Although the polymer is already dissolved, its increase in viscosity of the drug solution causes the drug to be retained somewhat longer in the desired application. This technique is common with ocular, nasal, and oral applications of drug solutions. 

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. 

Table I. Examples of Water-Soluble Polymers Used as Drug Delivery Matrices...

The rate of drug release (E) from the eroding matrix is controlled by (a) the chemical properties of the system - the hydrolytic and the neutralizing process at the boundary of the device, catalytic degradation of the polymer and the intrinsic backbone reactivity, and (b) several concomitant physical processes such as water diffusivity, water solubility, water partitioning, etc. 

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