Nanoparticle-in-microparticle oral drug delivery system of a clinically relevant darunavir/ritonavir antiretroviral combination

Nanonization has been extensively investigated to increase the oral bioavailability of hydrophobic drugs in general and antiretrovirals (ARVs) used in the therapy of the human immunodeficiency virus (HIV) infection in particular. We anticipated that in the case of protease inhibitors, a family of pH-dependent ARVs that display high aqueous solubility under the acid conditions of the stomach and extremely low solubility under the neutral ones of the small intestine, this strategy might fail owing to an uncontrolled dissolution-re-precipitation process that will take place along the gastrointestinal tract. To tackle this biopharmaceutical challenge, in this work, we designed, produced and fully characterized a novel Nanoparticle-in-Microparticle Delivery System (NiMDS) comprised of pure nanoparticles of the first-line protease inhibitor darunavir (DRV) and its boosting agent ritonavir (RIT) encapsulated within film-coated microparticles. For this, a clinically relevant combination of pure DRV and RIT nanoparticles was synthesized by a sequential nanoprecipitation/solvent diffusion and evaporation method employing sodium alginate as viscosity stabilizer. Then, pure nanoparticles were encapsulated within calcium alginate/chitosan microparticles that were film-coated with a series of poly(methacrylate) copolymers with differential solubility in the gastrointestinal tract. This coating ensured full stability under gastric-like pH and sustained drug release under intestinal one. Pharmacokinetic studies conducted in albino Sprague Dawley rats showed that DRV/RIT-loaded NiMDSs containing 17% w/w drug loading based on dry weight significantly increased the oral bioavailability of DRV by 2.3-fold with respect to both the unprocessed and the nanonized DRV/RIT combinations that showed statistically similar performance. Moreover, they highlighted the limited advantage of only drug nanonization to improve the oral pharmacokinetics of protease inhibitors and the potential of our novel delivery approach to improve the oral pharmacokinetics of nanonized poorly water-soluble drugs displaying pH-dependent solubility. Statement of significance: Protease inhibitors (PIs) are gold-standard drugs in many ARV cocktails. Darunavir (DRV) is the latest approved PI and it is included in the 20th WHO Model List of Essential Medicines. PIs poorly-water soluble at intestinal pH and more soluble under gastric conditions. Drug nanonization represents one of the most common nanotechnology strategies to increase dissolution rate of hydrophobic drugs and thus, their oral bioavailability. For instance, pure drug nanosuspensions became the most clinically relevant nanoformulation. However, according to the physicochemical properties of PIs, nanonization does not appear as a very beneficial strategy due to the fast dissolution rate anticipated under the acid conditions of the stomach and their uncontrolled recrystallization and precipitation in the small intestine that might result in the formation of particles of unpredictable size and structure (e.g., crystallinity and polymorphism) and consequently, unknown dissolution rate and bioavailability. In this work, we developed a sequential nanoprecipitation method for the production of pure nanoparticles of DRV and its boosting agent ritonavir in a clinically relevant 8:1 wt ratio using alginate as viscosity stabilizer and used this nanosuspension to produce a novel kind of nanoparticle-in-microparticle delivery system that was fully characterized and the pharmacokinetics assessed in rats. The most significant points of the current manuscript are: 1) Development of a sequential nanoprecipitation method to produce a fixed-dose combination of two antiretrovirals2) Design and characterization of a novel kind of nanoparticle-in-microparticle drug delivery system with high stability and low drug release in the stomach3) Demonstration for the first time of the lack of benefit of only drug nanonization in protease inhibitors4) Design of a new protocol for oral administration of solid formulations in rodents5) Achievement of significant increase of the oral bioavailability of darunavir6) Opening of new opportunities for more efficacious oral delivery of hydrophobic drug