Refining the in vitro release test method for a dapivirine-releasing vaginal ring to match in vivo performance

Diarmaid J. Murphy, Deanna Lim, Ryan Armstrong, Clare F. McCoy, Yahya Dallal Bashi, Peter Boyd, Tiffany Derrick, Patrick Spence, Brid Devlin, Karl Malcolm*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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Previously reported in vitro release test methods for drug-releasing vaginal rings containing poorly water soluble drugs have described use of water-alcohol systems or surfactant solutions in efforts to maintain sink conditions. Here, as part of efforts to more closely match in vitro and in vivo release for the 25 mg dapivirine matrix-type silicone elastomer vaginal ring for HIV prevention, we have investigated alternatives to the 1:1 v/v water/isopropanol medium described previously. Specifically, we evaluated dapivirine release from rings into (i) monophasic water/isopropanol mixtures of varying composition, and (ii) biphasic buffer/octanol systems using pH 4.2 and pH 7 buffers. The rate and mechanism of dapivirine release was dependent upon the isopropanol concentration in the release medium, in accordance with the observed trend in drug solubility. At 0 and 10% v/v isopropanol concentrations, dapivirine release followed a partition-controlled mechansim. For media containing ≥20% v/v isopropanol, in vitro release of dapivirine was significantly increased and obeyed permeation-controlled kinetics. Cumulative release of ~3.5 mg dapivirine over 28 days was obtained using a water isopropanol mixture containing 20% v/v isopropanol, similar to the ~4 mg dapivirine released in vivo. Dapivirine release into the biphasic buffer/octanol system (intended to mimic the fluid/tissue environment in vivo) was constrained by the limited solubility of dapivirine in the buffer component in which the ring resided, such that cumulative dapivirine release was consistently lower than that observed with the 20% v/v isopropanol in water medium. Release into the biphasic system was also pH dependent, in line with dapivirine’s pKa and with potential implications for in vivo release and absorption in women with elevated vaginal pH.
Original languageEnglish
JournalDrug Delivery and Translational Research
Early online date21 Oct 2021
Publication statusEarly online date - 21 Oct 2021


  • Vaginal ring
  • in vitro release testing
  • bio-relevant
  • drug release
  • dapivirine


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