A comprehensively validated IVRT method reliably discriminates sameness and differences between several topical clotrimazole creams.

In vitro release testing (IVRT) has gained increasing acceptance for use as a biowaiver for topical products intended for local action. Whereas the United States Food and Drug Administration (US FDA) has issued product specific guidances (PSGs) recommending IVRT for several products, the PSG for clotrimazole cream does not include an IVRT option. However, an important requirement to include supplemental selectivity in the validation process as described in the recent FDA draft guidance on IVRT studies for topical drug products has generally been conspicuously absent in the published literature describing the application of IVRT as a biowaiver. Supplemental selectivity involves the comparison of a reference product and altered formulations containing the same strength of the active pharmaceutical ingredient (API). In order to demonstrate supplemental selectivity, cream formulation containing the same API (clotrimazole), at the same strength (1 %) and in the same dosage form (cream) but manufactured using different excipients were used. This will help assess the impact that excipients may have on the release rate of clotrimazole and whether the method is capable of identifying differences in the microstructure and arrangement of matter (Q3) as an important performance parameter. In addition, products containing <30 % or >40 % clotrimazole to serve as negative controls were also included for the discriminatory power assessment. Hence, the primary objective was to develop and validate a simple, reliable, reproducible, and cost-effective in vitro technique in accordance with the recent draft FDA guidance to assess the "sameness" of topical creams containing 1 % clotrimazole. An in vitro release testing (IVRT) system was used and an IVRT method was developed and accordingly validated. The validated IVRT method showed the potential to accurately measure the release from 1 % clotrimazole creams and demonstrated supplemental selectivity and appropriate discriminatory power to identify "sameness" and/ or differences.

Synthetic Cassettes for pH-Mediated Sensing, Counting, and Containment.

As pH is fundamental to all biological processes, pH-responsive bacterial genetic circuits enable precise sensing in any environment. Where the unintentional release of engineered bacteria poses a concern, coupling pH sensing to the expression of a toxin creates an effective bacterial containment system. Here, we present a pH-sensitive kill switch (acidic termination of replicating population [acidTRP]), based on the Escherichia coli asr promoter, with a survival ratio of <1 in 106. We integrate acidTRP with cryodeath to produce a 2-factor containment system with a combined survival ratio of <1 in 1011 while maintaining evolutionary stability. We further develop a pulse-counting circuit with single-cell readout for each administered stimulus pulse. We use this pulse counter to record multiple pH changes and combine it with acidTRP to make a 2-count acid-sensitive kill switch. These results demonstrate the ability to build complex genetic systems for biological containment.