Various formulations for combination of the anti-HIV protease inhibitor darunavir (DRV) and TMC41629, a pharmacokinetic booster for DRV, were studied. TMC41629 (a BCS-IV compound) was formulated in capsules, as polyethylene glycol 400 (PEG400) solution, binary or ternary self-microemulsifying drug delivery system (SMEDDS), inclusion complex with hydroxypropyl-beta-cyclodextrin (HPbetaCD) or polyvinylpyrrolidone-co-vinylacetate 64 (PVP/VA64) extrudate. In addition, tablets were prepared using unmilled or micronized powder and a disintegrant. On co-administration with DRV tablets in dogs, DRV plasma concentration levels were boosted by TMC41629, the PVP/VA64 extrudate achieving the highest DRV levels (2-fold increase). Yet, with extrudate prepared with both compounds, no boosting effect was observed, likely due to transition of DRV from crystalline solvate to amorphous state. Therefore, a co-formulation, combining DRV as crystalline solvate with amorphous TMC41629, was developed. DRV/kappa-carrageenan 80/20% (w/w) beads coated with TMC41629 released at least 80% within 1h in 0.01M HCl with 0.5% sodium lauryl sulphate, TMC41629 dissolving faster than DRV. In dogs, the DRV exposure increased 2.7-fold with the TMC41629-coated beads relative to DRV alone, yet remained lower, but less variable, than following co-administration as separate formulations. Coating of TMC41629 on DRV/kappa-carrageenan beads is a suitable technique for co-formulation, whereby TMC41629 can function as a booster of DRV.