Merck & Co. Inc. may be positioning itself to compete in the HIV combination therapy market dominated by Gilead Sciences Inc. and ViiV Healthcare LLC, the joint venture of GlaxoSmithKline plc and Pfizer Inc.

Merck has in-licensed a pair of early stage compounds from Chimerix Inc. and Yamasa Corp. and unveiled plans to move an internal molecule into Phase IIb testing this fall.