In Situ Optical Interferometric Studies of the Growth and Dissolution Behavior of Paracetamol (Acetaminophen) Crystals. 3. Influence of Growth in the Presence of p-Acetoxyacetanilide

Application of UV dissolution imaging to pharmaceutical systems

UV-vis spectrometry is widely used in the pharmaceutical sciences for compound quantification, alone or in conjunction with separation techniques, due to most drug entities possessing a chromophore absorbing light in the range 190-800 nm. UV dissolution imaging, the scope of this review, generates spatially and temporally resolved absorbance maps by exploiting the UV absorbance of the analyte. This review aims to give an introduction to UV dissolution imaging and its use in the determination of intrinsic dissolution rates and drug release from whole dosage forms. Applications of UV imaging to non-oral formulations have started to emerge and are reviewed together with the possibility of utilizing UV imaging for physical chemical characterisation of drug substances. The benefits of imaging drug diffusion and transport processes are also discussed.

Crystallization of paracetamol from mixtures of ethanol and water in a planar oscillatory flow crystallizer: effect of the oscillation conditions on the crystal growth kinetics

Crystal growth kinetic data is reported for a planar oscillatory flow crystallizer.

Crystallization of paracetamol from aqueous solutions in a planar oscillatory flow crystallizer: effect of the oscillation conditions on the nucleation kinetics

Nucleation kinetic data is reported for a planar oscillatory flow crystallizer.

Precision measurement of the growth rate and mechanism of ibuprofen {001} and {011} as a function of crystallization environment

The growth rates of the {001} and {011} crystal faces of ibuprofen were measured as a function of the solution crystallisation environment from which the likely interfacial kinetic growth mechanisms were characterised.

The effects of additives on the growth and morphology of paracetamol (acetaminophen) crystals

It is well known that the presence of impurities can dramatically affect the nucleation, morphology, and chemical properties of crystals. Although literature is replete with examples of impurity or additive-induced modifications of crystals, few have examined the interaction of these compounds with distinct growing faces. In this study, we utilize atomic force microscopy (AFM) and scanning electron microscopy (SEM) to investigate the influence of two structurally related additives of paracetamol (acetaminophen) on its crystal morphology. We also probe, in situ, the effects of these additives on the morphology and growth rate of steps on the (0 0 1) face of the crystal. This study, in conjunction with further investigations, aims to establish the specific mechanisms of inhibition of these additives on each face of paracetamol, and provide a means of overcoming the poor compaction behaviour of paracetamol.

Dissolution kinetics of paracetamol single crystals

The dissolution anisotropy of paracetamol crystals grown in the presence and absence of the molecularly similar additive, p-acetoxyacetanilide (PAA) was studied under controlled conditions using a single crystal dissolution method in undersaturated aqueous solutions. Linear dissolution rates were determined for all the major habit faces by measuring their movement (regression) with time in a flow cell using a microscope. The rates of dissolution of particular faces of the pure material were distinctly different in crystals of different morphology grown at different supersaturations. The dissolution rates of [001] and [110] faces of crystals grown in the presence of PAA (6.02% w/w in solution) are higher than those of pure paracetamol. The results correlate with the distribution of strain in the crystal and support the concept that integral strain increases the solubility and hence the dissolution rate of the material. The mechanism of the dissolution process at the [001], [201;] and [110] faces was defined using optical microscopy and X-ray topography. At all undersaturations above 1% the dissolution studies yielded well developed, structurally oriented, etch pits on both [001] and [201;] faces while on the [110] face rough shallow etch pits were observed. On all three faces, this etch-pitting was considerably more widespread than the dislocation content of the sector and probably reflects a 2-dimensional nucleation process rather than a dislocation controlled mechanism.

Crystallization of paracetamol from solution in the presence and absence of impurity

The bulk crystallization of paracetamol has been examined under controlled conditions in the presence and absence of the additive p-acetoxyacetanilide (PAA), as a function of both supersaturation and additive levels. The induction time to nucleation was found to increase with increase in PAA concentration in solution. The product micro-crystals were characterized for shape and strain/defect content using electron and optical microscopy and X-ray Laue diffraction techniques, respectively. A change in crystal habit of the pure crystals from columnar (dominant [110]) to plate-like (dominant [001]) was observed to occur with an increase in supersaturation level, whilst the addition of PAA invariably led to the development of columnar crystals with an aspect ratio that varied with impurity level and supersaturation. HPLC showed the PAA to be incorporated into the crystals with an average segregation coefficient of 14-18% depending on the supersaturation. The ready incorporation of PAA is attributed to the molecular similarity of this molecule to that of the host material. The incorporation is shown to cause a significant increase in the mosaic spread, implying the development of a significant strain/defect content in the crystals. The influence of the impurity on the time to nucleation is probably due to its effect in blocking the development of the critical nucleus. The potential implications of such variations in morphology and strain content in the design of the physical and chemical properties of the resulting particulates are discussed.