Drug Delivery and Translational Research

, Volume 1, Issue 3, pp 238–246 | Cite as

Pharmacokinetics of UC781-loaded intravaginal ring segments in rabbits: a comparison of polymer matrices

  • Meredith R. Clark
  • Patrick F. Kiser
  • Andrew Loxley
  • Christopher McConville
  • R. Karl Malcolm
  • David R. Friend
Research Article


UC781 is a potent and poorly water-soluble nonnucleoside reverse transcriptase inhibitor being investigated as a potential microbicide for preventing sexual transmission of HIV-1. This study was designed to evaluate the in vivo release and pharmacokinetics of UC781 delivered from matrix-type intravaginal ring segments in rabbits. Three polymer matrices (polyurethane, ethylene vinyl acetate copolymer, and silicone elastomer) and two drug loadings (5 and 15 mg/segment) were evaluated in at least one of two independent studies for up to 28 days in vivo. Inter-study comparison of in vivo release, vaginal tissue, and plasma concentrations for similar formulations demonstrated good reproducibility of the animal model. Mean estimates for a 28-day in vivo release ranged from 0.35 to 3.17 mg UC781 per segment. Mean proximal vaginal tissue levels (adjacent to the IVR segment) were 8–410 ng/g and did not change significantly with time for most formulations. Distal vaginal tissue levels of UC781 were 6- to 49-fold lower than proximal tissue levels. Mean UC781 plasma levels were low for all formulations, at 0.09–0.58 ng/mL. All formulations resulted in similar UC781 concentrations in vaginal tissue and plasma, except the low loading polyurethane group which provided significantly lower levels. Loading dependent release and pharmacokinetics were only clearly observed for the polyurethane matrix. Based on these results, intravaginal ring segments loaded with UC781 led to vaginal tissue concentrations ranging from below to approximately two orders of magnitude higher than UC781’s EC50 under in vitro conditions (2.8 ng/mL), with little influence by polymer matrix or UC781 loading. Moreover, these findings support the use of rabbit vaginal pharmacokinetic studies in preclinical testing of microbicide intravaginal rings.


UC781 Microbicide Intravaginal ring Pharmacokinetics 



The support of Missy Peet and Devon Kyle of MPI Research, Inc., in coordination of the rabbit studies and sample bioanalytical analysis, is gratefully acknowledged. This work was funded by the United States Agency for International Development (USAID) under Cooperative Agreement GPO-A-00-08-00005-00. The views of the authors do not necessarily reflect those of USAID.


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Copyright information

© Controlled Release Society 2011

Authors and Affiliations

  • Meredith R. Clark
    • 1
  • Patrick F. Kiser
    • 2
    • 3
  • Andrew Loxley
    • 4
  • Christopher McConville
    • 5
    • 6
  • R. Karl Malcolm
    • 5
  • David R. Friend
    • 1
  1. 1.CONRAD, Department of Obstetrics and GynecologyEastern Virginia Medical SchoolArlingtonUSA
  2. 2.Department of BioengineeringUniversity of UtahSalt Lake CityUSA
  3. 3.Department of Pharmaceutics and Pharmaceutical ChemistryUniversity of UtahSalt Lake CityUSA
  4. 4.Particle Sciences Inc.BethlehemUSA
  5. 5.School of Pharmacy, Medical Biology CentreQueen’s University of BelfastBelfastUK
  6. 6.School of Pharmacy, Faculty of Health SciencesCurtin UniversityPerthAustralia

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