The Microsponge Delivery System (MDS) is a unique technology for the controlled release of topical agents and consists of macroporous beads, typically 10-25 microns in diameter, loaded with active agent. When applied to the skin, the MDS releases its active ingredient on a time mode and also in response to other stimuli (rubbing, temperature, pH, etc). MDS technology is being used currently in cosmetics, over-the-counter (OTC) skin care, sunscreens and prescription products. By delivering the active gradually to the skin, MDS-benzoyl peroxide formulations, for example, have excellent efficacy with minimal irritation. These are typical benefits from the use of the MDS.
A new high-performance liquid chromatographic procedure for the analysis of phenprobamate, a skeletal muscle relaxant in biologic fluids was developed. The method used a C18 reverse phase column, a mobile phase of methanol/acetonitrile/water (33:15:52), and UV detection at 215 nm. The assay procedure was applied to the determination of phenprobamate binding to rat and human plasma proteins using the equilibrium dialysis method. In addition, the red blood cell/plasma partitioning was determined in the whole blood of rats and humans. Phenprobamate exhibited a moderate binding to plasma proteins of rat (74.3 +/- 2.2 per cent) and human (80.5 +/- 1.1 per cent). The protein binding was concentration-independent in the range of 10 to 80 micrograms ml-1. Phenprobamate binding to plasma proteins was also determined in the presence of 10 micrograms ml-1 acetaminophen. The protein binding of phenprobamate was not significantly altered by acetaminophen (74.4 +/- 0.6 per cent for rat plasma; 75.7 +/- 1.6 per cent for human plasma). The distribution ratios of phenprobamate between the red blood cells and plasma were greater than unity, 1.86 and 1.59 in rat and human, respectively, indicating a preferential partitioning of the drug in the red blood cells.
Unusual serum profiles of phenprobamate, a centrally skeletal muscle relaxant, were observed in Sprague Dawley rats receiving multiple doses of phenprobamate suspension. The concentrations of phenprobamate were higher after the morning doses than after the evening doses, synchronizing with the day-night pattern of drug administration. Crossover studies were conducted to investigate the apparent time-dependent kinetics of phenprobamate. Phenprobamate emulsion was orally administered as a single dose to a group of six rats at 0900 hr and again, after a washout period of 3 days, at 2100 hr. Another group of six rats was treated similarly with intraperitoneal drug administration. Blood samples were collected at various times for 12 hr. The AUCs were 146.56 +/- 31.77 micrograms.hr/ml for the morning oral dose and 111.31 +/- 21.32 micrograms.hr/ml for the evening oral dose (P less than 0.001). Administered intraperitoneally, the AUCs were 179.89 +/- 37.50 and 185.58 +/- 28.51 micrograms.hr/ml for the morning and evening doses, respectively, the difference of which was not significant. The paired t test indicated a significant morning-evening difference in AUC following oral but not intraperitoneal drug administration. This suggests the absorption rather than metabolism as a contributing factor to the time-dependent kinetics of phenprobamate in rats.
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