Formulation development of a dapivirine-releasing subdermal implant for HIV prevention

There have been several significant advances in recent years around long-acting strategies for HIV pre-exposure prophylaxis, including DapiRing® (a 1-month dapivirine (DPV)-releasing vaginal ring), Apretude® (a cabotegravir intramuscular injection administered every two months), and Yeztugo® (a twice-yearly lenacapavir injection). With the goal of developing new drug delivery devices that can extend antiretroviral release for 12 months or longer, we report here our preliminary efforts to design a subdermal implant releasing the antiretroviral drug DPV. These reservoir-type rod implants (length 40 mm, cross-sectional diameters 2.5, 3.2, 3.5 or 4.0 mm) comprised a silicone elastomer core containing solid crystalline DPV (loading 10, 20 or 40 % w/w) and an open-ended non-medicated rate-controlling silicone elastomer membrane (thickness 0.5, 0.8 or 1.0 mm). DPV in vitro release rates could be modulated by adjusting the membrane thickness. Continuous in vitro DPV release ∼12 μg/day was demonstrated over 330 days, with sufficient residual drug content (∼87 mg/∼95 %) to extend release for at least 5 years. In particular, the study highlights the challenges in designing subdermal implants providing sufficient DPV release to maintain systemic/vaginal concentrations at protective levels.