Efficacy data for a reservoir intervaginal ring (IVR) using slow release tenofovir disoproxil fumerate (TDF), developed to deliver a daily dose of 2.4 mg/day over 28 days, was presented at CROI 2013 by James Smith from the CDC Atlanta, in an oral presentation and a poster.1,2
This ring delivered sufficient intracellular drug levels in upper and lower vaginal tissue and cervical tissue samples expected to provide protection (based on >1000 ng/mL required for efficacy in the Caprisa 004 study gel study), with some penetration but at lower levels in inguinal lymph nodes and rectal tissue.
The efficacy study included 12 female macaques, half of which used the active ring, half as controls, plus an additional six historical controls. Rings were inserted at baseline and changed monthly for four months, with vaginal exposure to SHIV given weekly for 16 weeks.
All macaques using the active ring were protected throughout the four months, remaining RNA and antibody negative, compared to 11/12 control animals who became infected after a median of 4 exposures, p<0.0004.
No safety concerns were raised during the study, including a lack of changes in microflora or menstrual cycle. Human phase I studies are expected to start in 3Q 2103.
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