20. Triumeq

2015 sales
: $803 million
2020 projection: $4.04 billion

GlaxoSmithKline's ($GSK) HIV drugs business, ViiV Healthcare, has been steamrolling lately, and it owes much of the recent success to combo treatment Triumeq.

U.S. regulators approved the med--which adds newcomer therapy Tivicay, a fast-launcher in its own right, to commonly used treatments abacavir and lamivudine--in August of 2014, and since then, it's been raking. Overall, it helped push the British pharma giant's HIV sales to £2.32 billion (about $3.37 billion) in 2015, a 54% leap over the year prior.

And those revenues have been critical for Glaxo, which has been looking to offset its losses in the respiratory department. Sales of behemoth Advair have plummeted on pressure from U.S. payers and European generics, one factor that led Glaxo to hang onto ViiV after previously announcing it was weighing a divestment.

Instead, Glaxo may wind up holding the unit and Triumeq closer than ever. If Pfizer ($PFE) wanted to sell out of its share of the joint venture, Witty told investors on the company's Q4 conference call, "there's no way we would turn away that opportunity." -- Carly Helfand (email | Twitter)

For more:
Glaxo's HIV unit ViiV aims to steal share from Gilead before patents bite
GSK, Pfizer partnership wins EU nod for HIV pill weeks after FDA approval
Glaxo's ViiV venture adds $5B combo pill to its HIV-fighting armory

20. Triumeq