Comparison of in vitro release testing methods for the release of DL-lactide from a silicone elastomer

Vicky-Leigh Young, Robert Malcolm, Peter Boyd

Research output: Contribution to conferencePosterpeer-review


What did you set out to achieve within your study/project?
As part of efforts to develop a modular-type multipurpose prevention technology (MPT) vaginal ring in which one of the modules incorporates an agent to maintain an acidic vaginal pH, the in vitro release of DL-lactide from a silicone elastomer and its subsequent conversion to lactic acid is described. Three in vitro release test methods have been assessed: 25mL 0.2% Tween solution adjusted to pH 4.2 and replenished daily; 25 mL 0.2% Tween solution (pH 4.2) with no daily replacement; 25mL 0.2% Tween solution (pH 4.2) in a 10 mL per day flow-through system. The first method is similar to methods currently used for marketed rings and other vaginal rings in development. The second method is designed to overcome the requirement for daily replacement of release medium. The third method is intended to represent the dynamics of fluid flow and loss in the vagina.

What is the key message from your study/project?
In all experiments, pH of the medium was significantly reduced over the study period, decreasing to an average pH of 2.77, 2.75 and 2.81 on Day 1 for Methods 1,2 and 3, respectively. With Method 1, overall extent of pH reduction was less than that for Method 2, attributed to the daily replenishment of the release medium which depleted LT in the ring therefore increasing pH. For Method 2, where the media was not changed, pH steadily reduced, reaching a constant low pH value (pH 2.5). In Method 3, pH remained constantly low (pH 2.66–2.63) between day 2–8 followed a slight increase in pH on days 9 and 10.

What were the lessons learned from your study/project?
This set of studies concluded that LT can be effectively incorporated into a silicone elastomer module and is released from the module, demonstrated by the detection of LT in the release medium. LT is hydrolysed to LA, either within the module by the penetration of the release medium or in the release medium, following the release of LT. A reduction in pH of the release medium is observed due to the production of LA. Although the three in vitro test methods investigated provide different release vs. time profiles; we do not know which of the three methods best mimics release in vivo. It is concluded that LT incorporated into a silicone elastomer has the potential to be useful in a modular MPT, delivering LA to decrease vaginal pH and provide an environment that inactivates HIV and treats/prevents bacterial vaginosis.
Original languageEnglish
Publication statusPublished - 02 May 2019
EventGlobal Health Symposium 2019 - Queen's University Belfast, Belfast, United Kingdom
Duration: 02 May 201903 May 2019


ConferenceGlobal Health Symposium 2019
Abbreviated titleGHS2019
Country/TerritoryUnited Kingdom
Internet address


  • vaginal ring
  • bacterial vaginosis
  • lactic acid
  • lactide


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