Limitations of the Dye-Based Method for Determining Vaginal Applicator Use in Microbicide Trials

Background: A dye-based method for determining applicator usage in microbicide trials has been developed to assess whether applicators have been exposed to vaginal fluid. Our objective was to evaluate this method on polypropylene HTI applicators that are being widely used in several effectiveness trials of microbicides. Methods: Study participants enrolled in a clinical trial assessing SPL7013 (VivaGel) inserted gel intravaginally twice daily for 14 days and returned used and unused applicators. Before staining, smears were prepared from each participant-inserted applicator, Gram stained and assessed independently for the presence of vaginal cells and bacteria. Of the 169 participant-inserted applicators, 168 (99%) had vaginal cells identified by Gram stain. Participant: Inserted applicators were stained with a 0.05% FD & C blue dye No. 1 solution and compared with 70 inserted positive control applicators and 70 unused negative control applicators. Intravaginally inserted applicators should stain turquoise, whereas unused applicators should not retain any stain. The individual responsible for labeling and preparing the applicators did not serve as an evaluator. Results: Under optimized conditions, the sensitivity and specificity ranged from 81% to 95% and 86% to 93%, respectively for single use and unused applicators. The dye-based method was only 47% to 77% sensitive for participant-inserted applicators obtained from women using gel twice daily. Conclusion: The dye test for HTI polypropylene applicators had a sensitivity of 47% to 95%, depending on the evaluator and whether gel was present in the vagina. The sensitivity was decreased with multiple gel applications. The dye-based method cannot be recommended for HTI polypropylene applicators to monitor product adherence.