Abstract
We present a novel approach for measuring topical microbicide gel dilution using optical imaging. The approach compares gel thickness measurements from fluorimetry and multiplexed low coherence interferometry in order to calculate dilution of a gel. As a microbicide gel becomes diluted at fixed thickness, its mLCI thickness measurement remains constant, while the fluorimetry signal decreases in intensity. The difference between the two measurements is related to the extent of gel dilution. These two optical modalities are implemented in a single endoscopic instrument that enables simultaneous data collection. A preliminary validation study was performed with in vitro placebo gel measurements taken in a controlled test socket. It was found that change in slope of the regression line between fluorimetry and mLCI based measurements indicates dilution. A dilution calibration curve was then generated by repeating the test socket measurements with serial dilutions of placebo gel with vaginal fluid simulant. This methodology can provide valuable dilution information on candidate microbicide products, which could substantially enhance our understanding of their in vivo functioning.
Highlights
Microbicide gels are topically acting products that are inserted into the vagina to inhibit infection by sexually transmitted pathogens, mainly HIV
Analysis of the In Vitro Experiments Optical path length measurements obtained by multiplexed low coherence interferometry (mLCI) were first used to calculate index of refraction, n, for each gel dilution with the equation optical path length (OPL) = n*t, where t is the known thickness of the calibration socket
We found that dilution changed the index of refraction of the gel, which affects the accuracy of mLCI measurements; this change was minimal
Summary
Microbicide gels are topically acting products that are inserted into the vagina to inhibit infection by sexually transmitted pathogens, mainly HIV. There have been mixed results in the successes of multiple Phase 3 microbicide trials of such gels [1,2] These trials evaluated gels that were not designed using knowledge of their intravaginal spreading mechanics and its effects upon drug delivery and retardation of viral migration to epithelial surfaces. Such information can contribute to the rational design of improved microbicide gel products. This knowledge is derived from a combination of experimental measurements relating to vaginal deployment and drug delivery [3,4], and objective computations that relate product properties and dosage regimens to drug delivery [5,6,7,8]. These measurements include rheological properties of gels, drug release rates, and the effects of contact with and dilution by ambient vaginal fluids
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