Nuclear magnetic resonance study of an ethyl cellulose sustained‐release delivery system II: Release rate behavior of tetracycline

The release rate behavior of tetracycline (TC) from a sustained‐release delivery system composed of an ethyl cellulose (EC) film and polyethyleneglycol (PEG) was studied using proton magnetic resonance (PMR) and UV spectroscopy. The optical density (OD) and spin–spin relaxation time (T₂) were measured after the films were immersed in di‐distilled water. The TC release rate was examined as a function of two variables: gradual changes in the relative amounts (% w/w) of the embedded TC and PEG. A high correlation was found between the fractional changes of T₂ relaxation time and the percent release of TC, as measured by means of UV spectroscopy. The results revealed that the TC release profile from EC film is strongly dependent on the amount of embedded TC. On the other hand, the amount of embedded PEG markedly affected the release rate and release time of TC. These changes were reflected in a pronounced shortening of the T₂ relaxation time. The improvement in the hydrophilic character of the EC polymer allowed better penetration and contact of water with the whole film matrix and enhanced the dissolution of TC.