The crystalline solid state is invaluable to both the pharmaceutical and fine chemical sectors. The advantages primarily relate to reducibility criteria required during processing of stable solid state materials and delivering purification, which is inherently performed by the crystal growth process. A major challenge is achieving control through crystallising solids with the desired physico-chemical properties. If this can be achieved the crystalline solid is of great financial and practical benefit. One emerging methodology for manipulating the solid crystalline form is the application of co-crystals. This work relates to key steps in the understanding of rational design of co-crystals utilizing crystal engineering concepts to determine systems before then applying screening criteria to the selected sub-set. Co-crystal screening is routinely undertaken using high-throughput solution growth. We report a low- to medium-throughput approach, encompassing both a melt and solution crystallization step as a route to the identification of co-crystals. Prior to solution studies, a melt growth step was included utilizing the Kofler mixed fusion method. This method allowed elucidation of the thermodynamic landscape within the binary phase diagram and was found to increase overall screening efficiency. This led to the discovery of a number of co-crystal systems with the co-former nicotinamide, with the single crystal structures determined for the following systems; R/S ibuprofen: nicotinamide, S ibuprofen: nicotinamide, R/S flurbiprofen: nicotinamide and salicylic acid: nicotinamide. To assess the crystallization and phase behaviours of determined co-crystals the R/S ibuprofennicotinamide system was selected and successful studies were undertaken determining the aqueous ternary phase behavior and the pre-nucleation speciation in methanol. There have, as yet, been a limited number of published examples which are concerned with pharmaceutical property enhancement by co-crystals, as vast proportion of the literature concerns the growth and isolation of these novel phases. To elucidate further the pharmaceutical relevance of co-crystals the properties of the R/S ibuprofen- nicotinamide system were then assessed showing a positive profile for this material.

Magister Pharmaceuticae - MPharm / The author’s objective was to follow the product life-cycle process of a novel antiretroviral, nevirapine formulation in South Africa, to generate and compile data to pursue market registration. Five supramolecular co-crystals, viz. nevirapine-saccharin (NVSC), nevirapine-DL-tartaric acid (NVTTA), nevirapine-maleic acid (NVMLE), nevirapine-glutaric acid (NVGLT) and nevirapine-salicylic acid (NVSLI) were reproduced and confirmed by powder X-ray diffraction (PXRD). A pre-formulation study ensued to identify the most appropriate co-former candidate to formulate a tablet dosage form comparative to the proprietor brand, Viramune®. The co-crystals were synthesized by the co-precipitation and solvent-drop grinding techniques and identified by hot stage microscopy (HSM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), fourier transform infra-red spectrophotometry (FTIR), PXRD and single X-ray diffraction (SXRD). The solubility, dissolution and antiviral activity profiles of these co-crystals were assessed and compared to pure NV and NV:co-former mixtures in a 1:1 ratio. The preliminary dissolution analysis applied the BP 2005 rotating-basket method with water as dissolution medium. Initially, the dissolution samples were assayed with UV/VIS spectrophotometry which led to a more convincing quantitative approach where dissolution samples were assayed by HPLC. Solubility data revealed a fivefold increase in solubility of NV co-crystallized with maleic acid. Dissolution data, however revealed NVGLT as the best performing co-crystal with a 59 % NV drug release in water (dissolution media) with the remaining 4 co-crystals all indicating an enhanced aqueous solubility of NV. The antiviral activity of all 5 co-crystals performed by the National Institute of Communicable Diseases of South Africa determined whether the co-crystals had an improved antiviral activity against HIV-1 compared to pure NV. The results indicated that NVSC and NVSLI had the greatest antiviral activity compared to pure NV and the remaining co-crystals. The pre-formulation results formed the basis for the selection of the best co-former candidate for a NV co-crystal tablet formulation by direct compression. All solid dosage form quality control tests according to the USP 364 was performed on the prototype co-crystal tablet and the Viramune® tablet. Comparative dissolution analysis to evaluate bioequivalence was conducted and assayed by HPLC. The dissolution analysis utilized 3 media, viz. HCl buffer (pH 1.2), acetate buffer (pH 4.5) and a phosphate buffer (pH 6.8) which displayed no similarity in the dissolution profile of the prototype and the proprietor brand. Solution stability of NV in these buffered media was assessed after 4 weeks exposure of the dissolution samples to cold chain (2 - 8 °C, 0 % RH) and accelerated environmental conditions (40 °C, 75 % RH). The results indicated no significant degradation of NV in the prototype co-crystal tablet and the proprietor brand during the accelerated stability tests. Cytotoxicity against a host cell 293T and antiviral activity against the pseudo-HIV-1 virus of the prototype and proprietor brand was further determined. The antiviral activity results were favourable for both the prototype co-crystal and the proprietor brand tablet.

The objective of this study was to develop a new method for co-crystal preparation which adhered to green chemistry principles, and provided advantages over conventional methods. A novel, solvent-free, high-power ultrasound (US) technique, for preparing co-crystals from binary systems, was chosen as the technology which could fulfil these aims. The application of this technology for solid state co-crystal preparation was explored for ibuprofen-nicotinamide (IBU-NIC), carbamazepine-nicotinamide (CBZ-NIC) and carbamazepine-saccharin (CBZ-SAC) co-crystals. The effect of different additives and processing parameters such as power level, temperature and sonication time on co-crystallisation was investigated. Characterisation was carried out using DSC, PXRD, FTIR, Raman and HPLC. In addition, an NIR prediction model was developed and combined with multivariate analysis (PLS) and chemometric pre-treatments. It was found to be a robust, reliable and rapid method for the determination of co-crystal purity for the IBU-NIC and CBZ-NIC pairs. Co-crystal quantification of US samples helped to optimise the US method. Finally, a model formulation of paracetamol containing 5% and 10% PEG 8000 was ultrasonicated at maximum power with different exposure times. A comparison of technological and physicochemical properties of the resulting tablets with those of the tablets obtained using the pressing method evidenced significant differences. This suggested that US energy dissipation (mechanical and thermal effects) was the main mechanism which caused the PAR form I tabletability to improve. It was found that the ultrasound–compacted tablets released the drug at a slower rate compared to pure PAR. This technique was shown to be useful for improving tabletability for low-compressible drugs without the need to use a conventional tabletting machine.

The objective of this study was to develop a new method for co-crystal preparation which adhered to green chemistry principles, and provided advantages over conventional methods. A novel, solvent-free, high-power ultrasound (US) technique, for preparing co-crystals from binary systems, was chosen as the technology which could fulfil these aims. The application of this technology for solid state co-crystal preparation was explored for ibuprofen-nicotinamide (IBU-NIC), carbamazepine-nicotinamide (CBZ-NIC) and carbamazepine-saccharin (CBZ-SAC) co-crystals. The effect of different additives and processing parameters such as power level, temperature and sonication time on co-crystallisation was investigated. Characterisation was carried out using DSC, PXRD, FTIR, Raman and HPLC. In addition, an NIR prediction model was developed and combined with multivariate analysis (PLS) and chemometric pre-treatments. It was found to be a robust, reliable and rapid method for the determination of co-crystal purity for the IBU-NIC and CBZ-NIC pairs. Co-crystal quantification of US samples helped to optimise the US method. Finally, a model formulation of paracetamol containing 5% and 10% PEG 8000 was ultrasonicated at maximum power with different exposure times. A comparison of technological and physicochemical properties of the resulting tablets with those of the tablets obtained using the pressing method evidenced significant differences. This suggested that US energy dissipation (mechanical and thermal effects) was the main mechanism which caused the PAR form I tabletability to improve. It was found that the ultrasound–compacted tablets released the drug at a slower rate compared to pure PAR. This technique was shown to be useful for improving tabletability for low-compressible drugs without the need to use a conventional tabletting machine.