Karthik Nagapudi

Manufacture of pharmaceutical co‐crystals using twin screw extrusion: A solvent‐less and scalable process

Pharmaceutical scientists are currently facing an increasing number of drug molecules with less than ideal properties such as poor solubility and lack of acceptable physical and chemical stability. Therefore, significant efforts in pharmaceutical sciences have concentrated on finding alternate solid forms and/or formulations with an aim of improving these properties. As part of these efforts, co-crystals have been identified as viable alternative solid forms, which in some instances may improve the drugability properties of a development candidate. Co-crystals have been defined as crystalline materials that comprise of two or more components that are solids at room temperature (in order to distinguish them from hydrates and solvates) held together by noncovalent forces. The distinction between a salt and a co-crystal lies in the fact that there is no proton transfer occurring between the constituents of a co-crystal. There has been an increased interest in cocrystals in the last few years and a number of publications have highlighted the beneficial properties of co-crystals. In order to be considered viable candidates for development, a scalable method to produce co-crystals must be established. Traditionally co-crystals have been prepared by grinding the constituents together.

Fast Surface Crystallization of Amorphous Griseofulvin Below Tg

ABSTRACTPurposeTo study crystal growth rates of amorphous griseofulvin (GSF) below its glass transition temperature (Tg) and the effect of surface crystallization on the overall crystallization kinetics of amorphous GSF.MethodsAmorphous GSF was generated by melt quenching. Surface and bulk crystal growth rates were determined using polarized light microscope. X-ray powder diffraction (XRPD) and Raman microscopy were used to identify the polymorph of the crystals. Crystallization kinetics of amorphous GSF powder stored at 40°C (Tg−48°C) and room temperature (Tg−66°C) was monitored using XRPD.ResultsCrystal growth at the surface of amorphous GSF is 10- to 100-fold faster than that in the bulk. The surface crystal growth can be suppressed by an ultrathin gold coating. Below Tg, the crystallization of amorphous GSF powder was biphasic with a rapid initial crystallization stage dominated by the surface crystallization and a slow or suspended late stage controlled by the bulk crystallization.ConclusionsGSF exhibits the fastest surface crystallization kinetics among the known amorphous pharmaceutical solids. Well below Tg, surface crystallization dominated the overall crystallization kinetics of amorphous GSF powder. Thus, surface crystallization should be distinguished from bulk crystallization in studying, modeling and controlling the crystallization of amorphous solids.

Selective and Potent Raf Inhibitors Paradoxically Stimulate Normal Cell Proliferation and Tumor Growth

Raf inhibitors are under clinical investigation, specifically in patients with tumor types harboring frequent activating mutations in B-Raf. Here, we show that cell lines and tumors harboring mutant B-Raf were sensitive to a novel series of Raf inhibitors (e.g., V600EB-Raf A375, IC50 on cells = 2 nmol/L; ED50 on tumor xenografts = 1.3 mg/kg). However, in cells and tumors with wild-type B-Raf, exposure to Raf inhibitors resulted in a dose-dependent and sustained activation of mitogen-activated protein kinase signaling. In some of these cell lines, Raf inhibition led to entry into the cell cycle, enhanced proliferation, and significantly stimulated tumor growth in vivo. Inhibition with structurally distinct Raf inhibitors or isoform-specific small interfering RNA knockdown of Raf showed that these effects were mediated directly through Raf. Either A-Raf or C-Raf mediated the Raf inhibitor–induced mitogen-activated protein kinase pathway activation in an inhibitor-specific manner. These paradoxical effects of Raf inhibition were seen in malignant and normal cells in vitro and in vivo. Hyperplasia of normal epithelial cells in the esophagus and the stomach was evident in mice with all efficacious Raf inhibitors (n = 8) tested. An implication of these results is that Raf inhibitors may induce unexpected normal cell and tumor tissue proliferation in patients. Mol Cancer Ther; 9(8); 2399–410. ©2010 AACR.

Amorphous Active Pharmaceutical Ingredients in Preclinical Studies: Preparation, Characterization, and Formulation

Abstract: A large number of the new pharmaceutical small molecules under development today are found to have poor water solubility. This in turn may lead to low bioavailability, which can have a significant impact on the development of the compound. Compounds with low bioavailability pose a greater challenge in early preclinical work involving animal studies, where obtaining maximum exposure is the primary goal especially in toxicology studies designed to establish the safe dose. From the standpoint of maximizing exposure, the amorphous phase is of great interest as pharmaceutical materials since it is the most metastable state and as such offers the potential of higher solubility and better bioavailability. However, the amorphous approach is not actively pursued in preclinical work owing to the tendency of the amorphous phase to crystallize thereby neutralizing the solubility advantage. This review focuses on (i) methods to generate the amorphous phase, (ii) methods to estimate the degree of crystallinity of the amorphous phase, (iii) methods to predict the stability of the amorphous phase against crystallization, and (iv) choice of polymers carrier and formulation of the amorphous phase for preclinical studies.

Application of Twin Screw Extrusion in the Manufacture of Cocrystals, Part I: Four Case Studies

The application of twin screw extrusion (TSE) as a scalable and green process for the manufacture of cocrystals was investigated. Four model cocrystal forming systems, Caffeine-Oxalic acid, Nicotinamide-trans cinnamic acid, Carbamazepine-Saccharin, and Theophylline-Citric acid, were selected for the study. The parameters of the extrusion process that influenced cocrystal formation were examined. TSE was found to be an effective method to make cocrystals for all four systems studied. It was demonstrated that temperature and extent of mixing in the extruder were the primary process parameters that influenced extent of conversion to the cocrystal in neat TSE experiments. In addition to neat extrusion, liquid-assisted TSE was also demonstrated for the first time as a viable process for making cocrystals. Notably, the use of catalytic amount of benign solvents led to a lowering of processing temperatures required to form the cocrystal in the extruder. TSE should be considered as an efficient, scalable, and environmentally friendly process for the manufacture of cocrystals with little to no solvent requirements.

Manufacture and Performance Evaluation of a Stable Amorphous Complex of an Acidic Drug Molecule and Neusilin

In this paper, we explore the use of Neusilin, an inorganic magnesium aluminometasilicate, to stabilize the amorphous form of an acidic drug Sulindac. Both cryomilling and ball milling of the drug with Neusilin were found to produce the amorphous phase. However, the ball-milled (BM) material exhibited superior physical stability when compared with the cryomilled material at 40°C/75% relative humidity. (13) C solid-state nuclear magnetic resonance investigation of the BM material revealed an acid-base reaction between Sulindac and Neusilin. Optimal milling conditions and the kinetics of salt formation were also established. As benchtop milling is a laboratory-scale process, a scalable process was developed to make Sulindac-Neusilin amorphous drug complex using hot-melt extrusion (HME). The dissolution properties of the resulting HME material was found to have been improved over the material made by benchtop milling while maintaining similar physical stability. The HME material was used to make tablets using a direct compression method. The HME tablets were found to have better dissolution properties than tablets made from crystalline Sulindac. For the broad class of acidic drugs containing the carboxyl moiety, inorganic silicates such as Neusilin would offer a better choice than organic polymers to stabilize the amorphous phase.

Quantification of compaction-induced crystallinity reduction of a pharmaceutical solid using 19F solid-state NMR and powder X-ray diffraction

19F solid-state nuclear magnetic resonance (NMR) was investigated as an analytical technique to quantify the amorphous phase in a fluorine-containing pharmaceutical candidate. The crystallinity of Compound 1 was calculated using two 19F T1 relaxation-based methods. The first method employs both the pure amorphous and the crystalline reference standards while the second method is model independent and utilizes a single standard. The 19F solid-state NMR results were confirmed with powder X-ray diffraction methods. From X-ray diffraction data, two linear calibration curves were obtained from blends of crystalline and amorphous Compound 1: one is based on the total integrated intensity of selected diffraction peaks and the other on the total intensity of the amorphous halo at 2θ positions that have no interference from crystalline diffraction peaks. The crystallinity of Compound 1 after compaction calculated by both 19F solid-state NMR methods was in excellent agreement with the results from the X-ray calibration curves. 19F solid-state NMR was shown to be a powerful technique in determining the amount of amorphous phase present in a pharmaceutical solid.

High-throughput screening and scale-up of cocrystals using resonant acoustic mixing

This paper explores the effectiveness of resonant acoustic mixing RAM for screening and scale up of cocrystals. 16 cocrystal systems were selected as test cases based on previous literature precedent. A 96 well plate set up in conjunction with zirconia beads was used for cocrystal screening using RAM. A success rate of 80% was obtained in the screen for plates containing solvent or solvent plus Zirconia beads. A proof of concept production of hydrated and anhydrous cocrystals of 1:1 Theophylline Citric acid system at a 400mg scale was demonstrated using solvent and bead assisted RAM. Finally the parameters affecting the scale up of 2:1 Theophylline Oxalic acid cocrystals was explored in a systematic fashion using a Design of Experiments DOE approach. The RAM parameters of acceleration and mixing time were optimized using the DOE approach. A quantitative XRPD method was developed to determine the extent of conversion to the cocrystal when using RAM Mixing time of 2h and an acceleration of 60G were determined to be optimal. The optimized parameters were used to demonstrate scale up of 2:1 Theophylline Oxalic acid cocrystals at an 80 gram scale with a net yield of 94%. RAM is thus established as an environmentally friendly mechanochemical technique for both high throughput screening and scaled up production of cocrystals.

Investigation of Phase Mixing in Amorphous Solid Dispersions of AMG 517 in HPMC-AS Using DSC, Solid-State NMR, and Solution Calorimetry.

Intimate phase mixing between the drug and the polymer is considered a prerequisite to achieve good physical stability for amorphous solid dispersions. In this article, spray dried amorphous dispersions (ASDs) of AMG 517 and HPMC-as were studied by differential scanning calorimetry (DSC), solid-state NMR (SSNMR), and solution calorimetry. DSC analysis showed a weakly asymmetric (ΔTg ≈ 13.5) system with a single glass transition for blends of different compositions indicating phase mixing. The Tg-composition data was modeled using the BKCV equation to accommodate the observed negative deviation from ideality. Proton spin-lattice relaxation times in the laboratory and rotating frames ((1)H T1 and T1ρ), as measured by SSNMR, were consistent with the observation that the components of the dispersion were in intimate contact over a 10-20 nm length scale. Based on the heat of mixing calculated from solution calorimetry and the entropy of mixing calculated from the Flory-Huggins theory, the free energy of mixing was calculated. The free energy of mixing was found to be positive for all ASDs, indicating that the drug and polymer are thermodynamically predisposed to phase separation at 25 °C. This suggests that miscibility measured by DSC and SSNMR is achieved kinetically as the result of intimate mixing between drug and polymer during the spray drying process. This kinetic phase mixing is responsible for the physical stability of the ASD.

High-throughput 96-well solvent mediated sonic blending synthesis and on-plate solid/solution stability characterization of pharmaceutical cocrystals.

A 96-well high-throughput cocrystal screening workflow has been developed consisting of solvent-mediated sonic blending synthesis and on-plate solid/solution stability characterization by XRPD. A strategy of cocrystallization screening in selected blend solvents including water mixtures is proposed to not only manipulate solubility of the cocrystal components but also differentiate physical stability of the cocrystal products. Caffeine-oxalic acid and theophylline-oxalic acid cocrystals were prepared and evaluated in relation to saturation levels of the cocrystal components and stability of the cocrystal products in anhydrous and hydrous solvents. AMG 517 was screened with a number of coformers, and solid/solution stability of the resulting cocrystals on the 96-well plate was investigated. A stability trend was observed and confirmed that cocrystals comprised of lower aqueous solubility coformers tended to be more stable in water. Furthermore, cocrystals which could be isolated under hydrous solvent blending condition exhibited superior physical stability to those which could only be obtained under anhydrous condition. This integrated HTS workflow provides an efficient route in an API-sparing approach to screen and identify cocrystal candidates with proper solubility and solid/solution stability properties.