OBJECTIVES: Combination microbicide vaginal rings may be more effective than 
single microbicide rings at reducing/preventing sexual transmission of HIV. 
Here, we report the pre-clinical development and macaque pharmacokinetics of 
matrix-type silicone elastomer vaginal rings containing dapivirine and 
darunavir.
METHODS: Macaque rings containing 25 mg dapivirine, 100 mg dapivirine, 300 mg 
darunavir or 100 mg dapivirine+300 mg darunavir were manufactured and 
characterized by differential scanning calorimetry. In vitro release was 
assessed into isopropanol/water and simulated vaginal fluid. Macaque vaginal 
fluid and blood serum concentrations for both antiretrovirals were measured 
during 28 day ring use. Tissue levels were measured on day 28. Ex vivo challenge 
studies were performed on vaginal fluid samples and IC50 values were calculated.
RESULTS: Darunavir caused a concentration-dependent reduction in the dapivirine 
melting temperature in both solid drug mixes and in the combination ring. In 
vitro release from rings was dependent on drug loading, the number of drugs 
present and the release medium. In macaques, serum concentrations of both 
microbicides were maintained between 10(1) and 10(2) pg/mL. Vaginal fluid levels 
ranged between 10(3) and 10(4) ng/g and between 10(4) and 10(5) ng/g for 
dapivirine and darunavir, respectively. Both dapivirine and darunavir showed 
very similar concentrations in each tissue type; the range of drug tissue 
concentrations followed the general rank order: vagina (1.8 × 10(3)-3.8 × 10(3) 
ng/g)  > cervix (9.4 × 10(1)-3.9 × 10(2) ng/g)  > uterus (0-108 ng/g)  > rectum 
(0-40 ng/g). Measured IC50 values were >2 ng/mL for both compounds.
CONCLUSIONS: Based on these results, and in light of recent clinical progress of 
the 25 mg dapivirine ring, a combination vaginal ring containing dapivirine and 
darunavir is a viable second-generation HIV microbicide candidate.