Development of a Raman method to follow the evolution of coating thickness of pellets.

CONTEXT: Although several methods have been investigated to measure the film thickness of tablets and its correlation with the dissolution behavior, much fewer such investigations exist for pharmaceutical pellets. OBJECTIVE: To study the possibility of measuring the film thickness and predicting the dissolution behavior of pellets produced in different fluid bed equipments with Raman spectroscopy. MATERIALS AND METHODS: Pyridoxine hydrochloride-layered pellets were produced and coated in two different Strea-1 equipments. Raman spectra were collected and analysed to set up a calibration model based on the film thickness data calculated from Camsizer analysis results. Dissolution tests were done according to Ph. Eur. standards. RESULTS: Raman spectroscopy proved to be a good tool in the measurement of film thickness. Polymer weight gain showed a linear correlation with film thickness but was a poor predictor of dissolution results below a threshold value. CONCLUSION: The Raman spectroscopic measurement of a small sample can provide accurate data of the film thickness. The investigation suggests that a threshold value might exist for the film thickness above which it can be used to judge future dissolution results.

Multivariate calibration of the degree of crystallinity in intact pellets by X-ray powder diffraction.

XRPD is the method of choice to determine crystalline content in an amorphous environment. While several studies describe its use on powders, little information is available on its performance on finished products. The method's use may be limited not only by the need of sample pretreatment and its validation but also by the propensity of some materials to recrystallize when exposed to heat or mechanical stress. In this work the authors describe an attempt at constructing a model based on the XRPD measurement of intact layered pellets using univariate methods based on peak heights and PLS regression. Results indicate that neither the goodness-of-fit (below 0.9 for all tested variables), nor the RMSEC values (above 5 for all tested variables) of any model based on peak height were good enough to consider them for everyday use. PLS regression however provided a model with improved characteristics (R(2)=0.9581, RMSEC=3.04) despite the low API content and individual loading characteristics also reflected the validity of the model. PLS analysis also indicated that a specific sample may be different in some formulation characteristic that did not register on other examinations. This further indicates the method's usefulness in the analysis of intact dosage forms.

Study of the recrystallization in coated pellets - effect of coating on API crystallinity.

Coated diltiazem hydrochloride-containing pellets were prepared using the solution layering technique. Unusual thermal behavior was detected with differential scanning calorimetry (DSC) and its source was determined using thermogravimetry (TG), X-ray powder diffraction (XRPD) and hot-stage microscopy. The coated pellets contained diltiazem hydrochloride both in crystalline and amorphous form. Crystallization occurs on heat treatment causing an exothermic peak on the DSC curves that only appears in pellets containing both diltiazem hydrochloride and the coating. Results indicate that the amorphous fraction is situated in the coating layer. The migration of drugs into the coating layer can cause changes in its degree of crystallinity. Polymeric coating materials should therefore be investigated as possible crystallization inhibitors.