HPMC-water gels

Gao, P. and Fagerness, P., Diffusion in HPMC gels. I. Determination of drug and water diffusivity by pulsed-field-gradient spin-echo NMR, Pharmaceutical Research, Vol. 12, No. 7, 1995, pp. 955-964. 

The swelling properties of HPMC as a sustained relea.se, hydrophilic matrix binder in tablets are well known. This polymer also has the ability to form a gel network to delay drug release (30,32.34.36,137). The use and efficiency of HPMC as a tablet and granule binder is comparable with methylcellulose. HPMC is available in a variety of grades with different solution viscosities and it is soluble in both water and hydroalcoholic solutions. However, HPMC is more soluble in cold water than hot but more dispersible in hot water than cold. Therefore, it is recommended to hydrate the HPMC powder in very hot water first, under agitation, and then to cool the solution down as quickly and as low as possible in order to avoid lumping problems. 

Rajabi-Siahboomi, A.R., BowteU, R.W., Mansfield, R, Davies, M.C. and Melia, C.D. (1996) Structure and behavior in hydrophUic matrix sustained release dosage forms 4. Studies of water mobility and diffusion coefficients in the gel layer of HPMC tablets using NMR imaging. Pharm Res, 13, 376-380. 

FIGURE 10 Self-diffusion coefficients of water across the gel layer of an HPMC tablet after 3 hours of hydration. The x axis is as shown in the original. (Reprinted with permission from ref. 17, Copyright 1996, Plenum.)... 

Ethyl methylcellulose (EMC) behaves like MC and HPMC and is soluble in cold water and forms gels on heating however, the gels are comparably weak. 

Hydroxypropylmethyl cellulose Hydroxypropyhnethyl cellulose (HPMC) (Figure 28.2) is water-soluble cellulose ether and it can be used as hydrophilic polymer for the preparation of controlled-release tablets. Water penetrates the matrix and hydrates the polymer chains, which eventually disentangle from the matrix. Drug release from HPMC matrices follows two mechanisms, drug diffusion through the swelling gel layer and release by matrix erosion of the swollen layer. " ... 

Hydroxypropylmethyl cellulose (HPMC) is a water-soluble cellulose ether that is mainly used in the preparation of controlled release tablets. Viscosity is the main variable responsible for controlling the release. The hydration and gel forming abilities of HPMC can be used to prolong the drug release of the active ingredient. 

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