Formulation Development of Topical Inserts Containing Doxycycline and Doxycycline Combined with Tenofovir Alafenamide and Elvitegravir for the Prevention of Sexually Transmitted Infections.

Despite advances in oral and injectable HIV prevention options and oral prophylaxis for sexually transmitted infections (STIs) of bacterial origin, there remains a critical need for effective on-demand topical (vaginal and rectal) products for pre- and post-exposure prophylaxis (PrEP and PEP). To fill this gap, we have developed single and first-in-kind multi-active topical inserts for bacterial STIs and HIV/STIs prevention. We have formulated two different inserts, one containing doxycycline (DOX) at 10, 50, and 100 mg doses for bacterial STI prevention, and a multipurpose prevention product (TED insert) that combines DOX (10 mg) with the antiretrovirals tenofovir alafenamide (TAF; 20 mg) and elvitegravir (EVG; 16 mg) to target both bacterial STIs and HIV. Inserts were manufactured using a simple and cost-effective process. Drug loading was within 95-105% of the labeled amount, confirming a robust manufacturing process. In vitro, the inserts disintegrated within 10 min with > 95% drug release within 60 min. The dissolution behavior of DOX inserts showed surface erosion but was affected by medium volume and drug amount. The inserts met key physicochemical targets: hardness (5-8 kg), friability (< 1%), moisture content (< 2%), and osmolality (< 550 mOsm/kg). Based on 6-month storage stability, DOX inserts maintained their physicochemical properties, indicating a shelf life of > 2 years. Preliminary 1-month stability of TED inserts under accelerated conditions showed preservation of their physicochemical properties. These data describe the formulation development and in vitro characterization of topical inserts containing DOX alone or in combination with antiretrovirals (TAF and EVG). Both inserts offer a novel, on-demand topical STI prevention option that supports flexible PrEP/PEP use by both women and men.