Wei-Qin Tong

Phase Behavior of Amorphous Molecular Dispersions II: Role of Hydrogen Bonding in Solid Solubility and Phase Separation Kinetics

No HeadingPurpose.To determine the factors influencing “solid solubility” and phase separation kinetics of drugs from amorphous solid dispersions.Methods.Solid dispersions of griseofulvin-poly(vinyl pyrrolidone) (PVP) and indoprofen-PVP were prepared using solvent evaporation technique. Dispersions demonstrating single Tg were exposed to 40°C/69% RH for 90 days. Drug solid solubility in the polymer and phase separation rates were determined from changes in Tg of solid dispersions. FTIR spectroscopy and XRD were used to characterize drug-polymer interactions and drug crystallinity, respectively.Results.Freshly prepared solid dispersion of up to 30% w/w griseofulvin and indoprofen were molecularly miscible with PVP. Hydrogen bonding was evident in indoprofen-PVP, but not in griseofulvin-PVP dispersions. When exposed to 40°C/69% RH, griseofulvin phase separated completely, whereas the solid solubility of indoprofen was determined as 13% w/w. The first-order rate constants of phase separation for 10%. 20%, and 30% w/w griseofulvin dispersions were estimated as 4.66, 5.19, and 12.50 (×102) [day−1], and those of 20% and 30% w/w indoprofen were 0.62 and 1.25 (×102) [day−1], respectively.Conclusions.Solid solubility of griseofulvin and indoprofen in PVP is ∼0% w/w and ∼13% w/w, respectively. Drug-polymer hydrogen bonding in indoprofen-PVP dispersions favors solid solubility. Phase separation rate of drug from the solid dispersions depends on the initial drug content and the nature of drug-polymer interactions.

Phase Behavior of Amorphous Molecular Dispersions I: Determination of the Degree and Mechanism of Solid Solubility

AbstractPurpose. To understand the phase behavior and the degree and mechanism of the solid solubility in amorphous molecular dispersions by the use of thermal analysis. Methods. Amorphous molecular dispersions of trehalose-dextran and trehalose-PVP were prepared by co-lyophilization. The mixtures were exposed to 23°C, 40°C, and 50°C [75% relative humidity (RH)] and 23°C (69% RH) storage conditions, respectively. Thermal analysis was conducted by modulated differential scanning calorimeter (MDSC). Results. Upon exposure to moisture, two glass transition temperatures (TgS), one for phase-separated amorphous trehalose (Tg1) and the other for polymer-trehalose mixture (Tg2), were observed. With time, Tg2 increased and reached to a plateau (Tgeq), whereas Tg1 disappeared. The disappearance of Tg1 was attributed to crystallization of the phase-separated amorphous trehalose. It was observed that Tgeq was always less than Tg of pure polymer. The lower Tgeq when compared to Tg of pure polymer may be the result of solubility of a fraction of trehalose in the polymers chosen. The miscible fraction of trehalose was estimated to be 12% and 18% wt/wt in dextran at 50°C/75% RH and 23°C/75% RH, respectively, and 10% wt/wt in PVP at 23°C/69% RH. Conclusions. Mixing behavior of trehalose-dextran and trehalose-PVP dispersions were examined both experimentally and theoretically. A method determining the “extent of molecular miscibility,” referred to as “solid solubility,” was developed and mechanistically and thermodynamically analyzed. Solid dispersions prepared at trehalose concentrations below the “solid solubility limit” were physically stable even under accelerated stability conditions.

Application of melt granulation technology to enhance tabletting properties of poorly compactible high-dose drugs

Using metformin HCl as the model drug and hydroxypropylcellulose (HPC) as the polymeric excipient, a melt granulation (MG) process that employs a twin-screw extruder has been developed to enhance compactibility of poorly compactible high-dose drug substances. A high (90%) drug-load tablet formulation, containing 1025 mg of active pharmaceutical ingredients and 109 mg of excipients, was produced. Drug-polymer-powder mixtures were melt granulated at a temperature above glass transition of HPC (130°C) but below melting point of metformin HCl (224°C). MG was compared with modified wet granulation (WG) and solvent granulation (SG) processes. Under identical compression force, the hardness of tablets produced was MG>SG>WG and the friability was MG<SG<WG. The hardness of WG tablets was highly sensitive to moisture content both during compression and subsequent storage, and, although not to the same extent, the hardness of SG tablets was also affected by loss-on-drying levels. MG provided a robust manufacturing process with highest compactibility and lowest friability that were not sensitive to changes in atmospheric moisture level. The process can decrease tablet sizes of high-dose drugs and combination products by decreasing the need for relatively large amounts of excipients generally used to overcome physicochemical limitations of drug substances.

Application of Melt Granulation Technology Using Twin-screw Extruder in Development of High-dose Modified-Release Tablet Formulation

Development of modified-release oral tablets of drug products usually requires release-modifying polymers at the level of above 50% of the total weight. This makes the development of high-dose products, especially with doses in the range of 750-1000 mg, difficult because the tablet size becomes unacceptably high. This report presents the development of high-dose modified-release formulation of an active pharmaceutical ingredient (API), imatinib mesylate, with a drug load of approximately 90%, by melt granulation using a twin-screw extruder. For an 800 mg dose, 956 mg of drug substance (salt) was needed and the final weight of tablet was approximately 1074 mg. By carefully selecting polymers based on their physicochemical properties, the release rate could be modified between desired times of 4 to >10 h for the total drug release. Mixtures of API and polymer were melt granulated at 185 °C, which is below the melting point of API (212 °C) but above the glass transition temperatures of polymers used. The confocal Raman microscopic imaging revealed that the API remained as unmelted, crystalline particles, and polymers were finely distributed on the surface and in between API particles. The formulations were found to be robust as no change in tableting and drug release properties was observed when manufacturing parameters were altered to challenge the process. The in vivo modified-release properties of formulations were demonstrated in human pharmacokinetic studies.