Differential thermal analysis as screening technique for candidate adjuvants in a parenteral formulation: cephradine for injection

Effect of carrier excipient and processing on stability of indorenate hydrochloride/excipient mixtures

The purpose of this investigation was to determine the solid-state chemical stability of a model drug, indorenate hydrochloride, as a function of carrier excipient and mixing process. Physical mixtures and granules were prepared by tumble mixing and alcoholic granulation with and without binder. Stability of the mixtures was estimated using differential scanning calorimetry and isothermal degradation studies at 40, 50, and 60 degrees C. Average first-order degradation constants at 25 degrees C, extrapolated from isothermal studies, were much lower for indorenate hydrochloride after tumbling mixing with microcrystalline cellulose (3.45 x 10(-5) day-1) than those obtained after tumbling mixing with lactose (112.0 x 10(-5) day-1). Distribution of the drug on the excipient's surface, through granulation with and without Povidone, increased the average drug degradation rates in granules with microcrystalline cellulose (36.2 x 10(-5) day-1) as well as in granules with lactose (326 x 10(-5) day-1). Partially amorphous lactose (spray-dried lactose) showed higher average degradation rates (310.5 x 10(-5) day-1) than crystalline lactose (199.3 x 10(-5) day-1). It appears that the amorphous portion of the drug as well as that of reacting excipients play a major role in affecting the reaction rate. The calorimetric studies showed a strong solid-solid interaction between indorenate hydrochloride and lactose, suggesting chemical incompatibility. This strong solid-solid interaction was characterized by disappearance of typical transition peaks of lactose at temperatures above 200 degrees C and the development of new peaks at about 130-170 degrees C. No major changes in transition peaks were observed in mixtures of microcrystalline cellulose and indorenate hydrochloride, suggesting chemical compatibility. Calorimetric results allow the prediction of the chemical incompatibility between indorenate hydrochloride and lactose observed in isothermal degradation studies.

Drug adjuvant interaction study using DSC supported by isothermal method

Extensive work has been done in the field of drug adjuvant interaction studies using differential scanning calorimetry (DSC), but conclusive interpretive techniques could not be reached since very few workers supplemented their work by conventional isothermal stability testing methods. This work compared the drug adjuvant thermogram with results obtained from isothermal stability studies and used it to reiterate the results of the drug adjuvant thermograms. In the formulation of ascorbic acid in a cosmetic preparation, the various adjuvants were tested for interactions first by the isothermal stability testing technique, which was followed by DSC scanning of the drug adjuvant. The results of the two methods were compared and correlated.

Application of differential scanning calorimetry to the study of solid drug dispersions

The present study describes the application of differential scanning calorimetry (DSC) to ascertain the crystalline state of a drug with a melting point of approximately 53 degrees C after dispersion on hydrophilic carriers by either simple mixing or by fusion. The carriers examined include polyethylene glycol 6000 and colloidal silicon dioxides. The most interesting of the systems investigated, in which the drug is gradually transformed from the crystalline to the amorphous state at room temperature, are physical mixtures of the drug and colloidal silicon dioxides. The crystalline transformation is manifested by the gradual decrease in the endothermic transition energy of the physical mixture with time. The crystalline transformation is characteristically biphasic with initially fast first-order kinetics, followed by a slow conversion process. The rate of transformation is dependent on the drug-silicon dioxide ratio, temperature, and certain physical properties of the silicon dioxides. An inverse relationship exists between transition energy and the in vitro dissolution rate of the drug in the physical mixtures with silicon dioxide. This suggests that DSC may provide a useful method for evaluating the effects of formulation variables upon dissolution rate.