Dissolution properties of piroxicam powders and capsules as a function of particle size and the agglomeration of powders

The poor dissolution characteristics of relatively insoluble drugs have lon g been a problem to the pharmaceutical industry. An example is piroxicam, a highly potent anti-inflammatory agent. In many countries, a large number o f generic piroxicam products are available to the prescriber. The aim of th is study was to investigate the cause of the dissolution problems experienc ed by manufacturers of generic piroxicam capsules. Two raw material batches and the dissolution properties of several piroxicam capsules were studied. Differential scanning calorimetry (DSC) and X-ray powder diffraction (XRPD ) results showed that the two raw material samples were identical with resp ect to polymorphic modification. The particles of powder 1 were smaller tha n those of powder 2, but the dissolution of powder 1 was much slower than t hat of powder 2. The dissolution results for the capsules showed a marked d ifference among different brands, with capsule C not meeting the USP tolera nce. Adding surfactant to the dissolution medium increased the dissolution of both powder 1 and capsule C. Failure of powder 1 or capsule C to meet US P dissolution criteria could result in differences in product efficacy, as well as in potential side effects. Such observations should be taken into a ccount along with other relevant considerations when decisions regarding th e generic substitution of oral piroxicam products are made.