The USP Performance Verification Test, Part II: collaborative study of USP's Lot P Prednisone Tablets.

PURPOSE: Periodic performance verification testing (PVT) is used by laboratories to assess and demonstrate proficiency and for other purposes as well. For dissolution, the PVT is specified in the US Pharmacopeia General Chapter Dissolution <711> under the title Apparatus Suitability Test. For Apparatus 1 and 2, USP provides two reference standard tablets for this purpose. For each new lot of these reference standards, USP conducts a collaborative study. METHODS: For new USP Lot P Prednisone Tablets, 28 collaborating laboratories provided data. The study was conducted with three sets of tablets: Lot O open label, Lot O blinded, and Lot P blinded. The blinded Lot O data were used for apparatus suitability testing. RESULTS: Acceptance limits were determined after dropping data due to failure of apparatus suitability, identification of data as unusual on control charts, or protocol violations. CONCLUSIONS: Results yielded acceptance criteria of (47, 82) for Apparatus 1 and (37, 70) for Apparatus 2. Results generally were similar for Lot P compared to results from Lot O except that the average percent dissolved for Lot P is greater than for Lot O with Apparatus 2.

Carbon fiber microelectrodes with multiple sensing elements for in vivo voltammetry.

Electrically evoked dopamine release was monitored in the striatum of anesthetized rats using voltammetric microelectrode assemblies with two to four separately addressable carbon fiber sensing elements. The sensing elements were disk-shaped, had a diameter of about 1 microm, and were separated from each other by less than 15 microm. The microelectrodes were used to monitor extracellular dopamine at multiple depths beneath the brain surface during electrical stimulation of the medial forebrain bundle. When the sensing elements were 10-15 microm apart, the stimulus responses at each element were distinct, suggesting that each response was representative of a distinct recording site. The possibility of performing measurements at distinct but closely spaced sites provides a potential route to high spatial resolution information about extracellular events. On the other hand, when the individual sensing elements were about 1 microm apart, similarities between the observed stimulus responses suggest that the multiple elements were recording from a single site. The ability to perform multiple chemical measurements at a single site presents several opportunities for new approaches to the in vivo study of neurochemistry.