Solvent-Assisted Hot Melt Extrusion of a Thermally Labile, High Melting Point Compound.

Molecular dispersions are a highly effective method of increasing bioavailability for a poorly soluble active pharmaceutical ingredient (API) and can be prepared on a large scale by hot melt extrusion (HME). Processing thermally labile active pharmaceutical ingredients (APIs) via HME is generally more difficult, with operating temperatures limited to below that of the API melting point. API melting is considered essential to facilitate the formation of a fully homogeneous amorphous system. Processing below the melting point renders the system much more susceptible to residual crystalline content; hence, HME is not suitable for APIs which degrade upon melting. In the following work, meloxicam (MEL) was used as a model API, possessing properties of high melting temperature and thermal lability. In this proof of concept work, a modified HME method, termed solvent-assisted HME, was used to overcome this issue and prepare an amorphous solid dispersion using HME, wherein a solvent was incorporated in the formulation blend during extrusion and removed post-processing. Formulations containing 10%wt meloxicam (MEL) and 90%wt polyvinylpyrrolidone vinyl acetate (PVPVA) copolymer were extruded using a twin-screw extruder at temperatures below the melting point of MEL. Dimethylformamide (DMF) solvent was added directly into the extruder barrel through a liquid addition port, resulting in extrudate products having a higher conversion of API to the amorphous form. The incorporation of solvent allowed a significant reduction in processing temperatures due to its increased mobility, while also driving the conversion of the API to its amorphous form. The solvent was successfully reduced through a secondary drying step using a vacuum oven. This advancement has demonstrated the potential for thermally labile APIs to be processed via HME expanding the applications of this technology.

Crystallization pathways and kinetics of carbamazepine-nicotinamide cocrystals from the amorphous state by in situ thermomicroscopy, spectroscopy, and calorimetry studies.

The work presented here was motivated by the premise that the amorphous state serves as a medium to study cocrystal formation. The molecular mobility inherent to amorphous phases can lead to molecular associations between different components such that a single crystalline phase of multiple components or cocrystal is formed. Cocrystallization pathways and kinetics were investigated from amorphous equimolar phases of carbamazepine and nicotinamide using hot-stage polarized microscopy (HSPM), hot-stage Raman microscopy (HSRM), differential scanning calorimetry (DSC), and X-ray powder diffraction (XRPD). Nonisothermal studies revealed that amorphous phases generate cocrystals and that thermal history affects crystallization pathways in significant ways. Two different pathways to cocrystal formation from the amorphous phase were identified: (1) at low heating rates (3 degrees C/min) a metastable cocrystalline phase initially nucleates and transforms to the more stable cocrystalline phase of CBZ-NCT, and (2) at higher heating rates (10 degrees C/min) individual components crystallize, then melt and the stable cocrystalline phase nucleates and grows from the melt. Isothermal studies above the T(g) of the amorphous equimolar phase also confirm the nucleation of a metastable cocrystalline phase from the amorphous state followed by a solid phase mediated transformation to the stable cocrystalline phase. Cocrystallization kinetics were measured by image analysis and by thermal analysis from small samples and are described by the Avrami-Erofeev model. These findings have important implications for the use of amorphous phases in the discovery of cocrystals and to determine the propensity of cocrystallization from process-induced amorphization.

Solubilization by cosolvents. Establishing useful constants for the log-linear model.

The purpose of this study was to develop constants for the log-linear cosolvent model, thereby allowing accurate prediction of solubilization in the most common pharmaceutical cosolvents: propylene glycol, ethanol, polyethylene glycol 400, and glycerin. The solubilization power (sigma) of each cosolvent was determined for a large number of organic compounds from the slope of their log-solubility vs. cosolvent volume fraction plots. The solubilization data at room temperature were either experimentally determined or obtained from the literature. The slopes of the nearly linear relationship between solubilization power and solute hydrophobicity (logK(ow)) were obtained by linear regression analysis for each considered cosolvent. Thus, knowing or calculating a compound's partition coefficient is all that is needed to predict solubilization.

Relationship between polysorbate 80 solubilization descriptors and octanol-water partition coefficients of drugs.

The molar solubilization capacities (kappa) and the molar micelle-water partition coefficients (K(M)(N)) in Polysorbate 80 of several drugs (including barbiturates, steroids, and benzoic acid derivatives) are related to their log octanol-water partition coefficients (logP). Both kappa and K(M)(N) values were calculated from solubility versus Polysorbate 80 concentration profiles, which were either experimentally determined or obtained from the literature. There is a linear relationship between logP of the tested compounds and the logarithm of the molar micelle-water partition coefficient (logK(M)(N)). On the other hand molar solubilization capacities are nearly independent of logP. It is shown that the ability of Polysorbate 80 to solubilize a drug can be predicted from its logP value.

A spin filter method for continuous evaluation of hemolysis.

A novel method for quantifying hemolysis is described. This method uses a spin filter to separate the free hemoglobin from the red blood cells suspended in the test solution. This procedure enables the use of a closed loop system that continuously measures hemolysis spectrophotometrically. It is shown that hemolysis does not always stop after the solution has been quenched with normal saline. In fact, the process of hemolysis induced by chemicals such as potassium oleate is relatively slow.

Buffer capacity and precipitation control of pH solubilized phenytoin formulations.

The main objective of this investigation is to develop a phenytoin (DPH) intravenous formulation that does not precipitate upon dilution. The effect of the buffer capacity at pH 12 of several DPH formulations on the extent and lag-time of DPH precipitation upon dilution with Sorensen's phosphate buffer (SPB) is evaluated. DPH precipitation was evaluated by means of static and dynamic in vitro dilution methods. It is shown that an increase in the formulation buffer capacity decreases substantially the extent of DPH precipitation and increases the lag-time for precipitation. In addition, a comparison between static and dynamic in vitro methods to measure precipitation is presented.

Degradation kinetics of 4-dedimethylamino sancycline, a new anti-tumor agent, in aqueous solutions.

The kinetics of degradation of the new anti-tumor drug, 4-dedimethylamino sancycline (col-3) in aqueous solution at 25oC were investigated by high-pressure liquid chromatography (HPLC) over the pH-range of 2-10. The influences of pH, buffer concentration, light, temperature, and some additives on the degradation rate were studied. The degradation of col-3 was found to follow first order kinetics. A rate expression covering the degradation of the various ionic forms of the drug was derived and shown to account for the shape of the experimental pH-rate profile. Under basic conditions, the degradation of col-3 involves oxidation, which is catalyzed by metal ions and inhibited by EDTA and Sodium bisulfite.

Spectrophotometric determination of acidity constants of 4-dedimethylamino sancycline (Col-3), a new antitumor drug.

A spectrophotometric technique was used to determine the acidity constants of 4-dedimethylamino sancycline (Col-3), a new antitumor drug. The apparent pKa values of Col-3 in 0.5% methanol aqueous media at approximately 25 degrees C with a constant ionic strength of 0.2 were calculated manually and graphically to be 5.64 +/- 0.17 (pKa1) and 8.35 +/- 0.07 (pKa2). In addition, the computer program SQUAD was used to confirm Col-3 pKa values. The pKa values obtained by SQUAD were pKa1 5.63 +/- 0.14 and pKa2 8.39 +/- 0.04. These results are in agreement with the tetracycline-like structure of Col-3.

Solubilization of diazepam.

Several attempts to increase diazepam solubility are in the literature. This study discusses these different solubilization approaches. Specific reference is given to the rationale in the application of pH control, cosolvency, surfactants, and cyclodextrins. It was found than cosolvency is a more attractive means of solubilizing diazepam than either pH control, surfactants, or cyclodextrins. Advantages, assumptions, and limitations of these diazepam solubilization techniques are also described.

Lysis of human red blood cells. 4. Comparison of in vitro and in vivo hemolysis data.

The dynamic in vitro method developed by the authors and other available in vitro methods were used to determine the degree of hemolysis induced by several cosolvent vehicles that have previously been evaluated in vivo. The in vitro data generated for each of these vehicles was compared with the in vivo hemolysis data to assess the ability of the method to estimate in vivo hemolysis. The results show that the in vitro data generated by the dynamic method are in agreement with the in vivo data for each vehicle. Therefore, the potential for formulations to induce intravascular hemolysis after injection can be determined by this dynamic in vitro method. With this information, hemolytically safe formulations can more easily be prepared.