Vertex Pharmaceuticals Inc. said Wednesday that it will more prominently display warnings of possible side effects on the US labels of its blockbuster hepatitis C drug Incivek, following reports of a small number of fatalities.

A known side effect of Incivek is skin rash, and that was noted on the drug’s original label following its US approval in mid 2011. Cambridge-based Vertex said Wednesday that the updating of the US label “follows reports of a small number of fatal skin reactions in patients who continued to receive Incivek combination therapy after a serious skin reaction was identified.”