Severe, potentially life-threatening and fatal skin reactions have been reported in people living with HIV using Merck’s integrase inhibitor Isentress (raltegravir), according to an update to the drug’s package insert announced by the U.S. Food and Drug Administration on Wednesday, November 2.

The reactions include cases of Stevens-Johnson syndrome and toxic epidermal necrolysis, two severe disorders. Other allergic (hypersensitivity) reactions have been reported and are associated with systemic symptoms along with organ problems, including liver failure.

If a skin reaction arises, people living with HIV using the drug are advised to contact their health care providers. It may be necessary to discontinue Isentress—along with other suspect medications—immediately if signs or symptoms of severe skin reactions or hypersensitivity reactions develop.

Signs and symptoms include, but are not limited to, severe rash or rash accompanied by fever, generally ill feeling, extreme tiredness, muscle or joint aches, blisters, oral lesions, eye inflammation, facial swelling, breathing difficulty, swelling of the eyes, lips and mouth, and/or signs and symptoms of liver problems (such as yellowing of the skin or whites of the eyes, dark or tea colored urine, pale colored stools/bowel movements, nausea, vomiting, loss of appetite, or pain, aching or sensitivity on the right side below the ribs).

Though the FDA did not specifically comment on the frequency of these skin reactions among people living with HIV using Isentress, the reactions are believed to be rare occurrences.