Effect of solid state transition on the physical stability of suspensions containing bupivacaine lipid microparticles.

Bupivacaine lipid microparticles were prepared and evaluated as a parenteral sustained-release dosage form for postoperative pain management. Bupivacaine free base was incorporated into a molten tristearin matrix and lipid micro-particles were subsequently formed from this molten mixture by a spray-congealing process. A 3% injectable bupivacaine lipid microparticle suspension was prepared by dispersing 30% bupivacaine lipid microparticles in an aqueous medium containing carboxymethylcellulose (CMC), mannitol, and Tween 80. Upon room temperature storage, the fluid suspension gradually changed into a nonflowing semisolid (gelation) as a result of crystal growth of bupivacaine. However, suspensions prepared with bupivacaine lipid microparticles that were previously annealed at an elevated temperature remained fluid upon long-term storage. Differential scanning calorimetry (DSC), x-ray powder diffraction (XRPD), and isoperibol solution calorimetry were used to investigate the changes in the solid-state properties of tristearin and bupivacaine in the lipid microparticles before and after the heat treatment. The DSC and XRPD results indicate that after 24 hours of heating at 40 degrees C, tristearin was completely converted from the unstable alpha form to the stable beta form. Using the isoperibol solution calorimetric method, bupivacaine was found to transform into a more stable form after the lipid microparticles were heated at 60 degrees C for 24 hours. The generation of the unstable solid forms of tristearin and bupivacaine was attributed to the resolidification of both components from the molten mixture during the spray-congealing process.

In vitro characterization of polyorthoester microparticles containing bupivacaine.

Laboratory-scale spray-congealing equipment was utilized to fabricate injectable microparticles consisting of polyorthoester and bupivacaine. Operating conditions for the spray-congealing process were optimized to produce microparticles with the desired shape and particle size to yield acceptable syringeability and injectability. Characterizations were performed to determine the chemico-physical properties of polyorthoester before and after microparticle fabrication. Microparticles with different drug loadings and comparable particle sizes were produced, and their in vitro drug-release profiles were determined. The in vitro drug release of microparticles with a high drug loading was markedly faster than those with a low drug loading. This is partially attributed to a more significant initial burst-drug release of the microparticles with a high drug loading. The microparticles have demonstrated the potential to be used for long-acting postsurgery pain management by local injection.

The development of an injection-molding process for a polyanhydride implant containing gentamicin sulfate.

A production-scale manufacturing process has been developed for polyanhydride/gentamicin sulfate implants for the treatment of osteomyelitis. Gentamicin sulfate was first dried to an acceptable moisture level by using a tumble vacuum dryer. Dried gentamicin sulfate powder and polyanhydride granules were separately fed into the twin-screw extruder at a pre-determined metering rate using a gravimetric feeding device. The extruded molten mixture was solidified to form strands which were subsequently cut into pellets by using a pelletizer. The pellets were characterized with respect to copolymer molecular weight and drug content uniformity. The pellets were later fed into production-scale injection-molding equipment for implant fabrication. The injection-molding cycle was developed and evaluated in terms of cycle reproducibility. Implants were tested and shown to yield an oriented skin-core structure exhibiting a desirable in-vitro drug release profile.

Effect of gamma-radiation on a polyanhydride implant containing gentamicin sulfate.

Septacin, a polyanhydride implant containing gentamicin sulfate, was sterilized by gamma-radiation. Its copolymer molecular weight (M(w) by GPC) was increased after this radiation. No cross-linking was shown in the radiated samples as no gel content was found by the filtration method. The chemical structure as detected by 1H NMR for non-radiated and radiated samples was comparable. For samples radiated at higher dose levels (70-100 kGy), the IR spectra showed that the intensity of absorbance attributable to the C-H stretching vibration (at 2852 and 2927 cm(-1)) was attenuated, indicating free-radical formation or loss of hydrogen atoms from C-H bonds. However, the mass spectra for the gamma-radiated and the non-radiated controls after they were completely depolymerized in methylene chloride were virtually identical. Therefore, it could be concluded that the increase in copolymer molecular weight for radiated Septacin was a result of chain extension in the copolymer backbone during radiation. In addition, wide-angle X-ray diffraction and polarizing light microscopy (PLM) revealed a change in the physical structure of the radiated copolymer. There was an increase in crystallinity of the copolymer with increasing radiation doses; the greatest increase in crystallinity occurred at the dose range of 70-80 kGy, which was also shown to result in the greatest molecular-weight increase. The crystalline morphology of the samples as detected by PLM was not altered by gamma-radiation, regardless of the dose levels.