Drugs against one type of hepatitis may activate another, sometimes with fatal consequences, Europe's medicines watchdog warned on Friday.
The medicines, which are highly effective against hepatitis C, may trigger latent hepatitis B in patients infected with both types, the European Medicines Agency said in a statement.
It named the antivirals Daklinza, Exviera, Harvoni, Olysio, Sovaldi and Viekirax used to treat chronic hepatitis C, an infectious liver disease.
"Cases of the return of previously inactive hepatitis B infection, which can be fatal, have been reported in patients treated," with this class of drug, the agency said in a statement announcing the findings of a probe.
There have been only about 30 cases of hepatitis B reactivation out of thousands of patients taking the drugs, the agency said. And there was not enough information to draw a conclusion on cancer risk.
But a special risk assessment committee of the agency recommended that all patients be screened for hepatitis B virus before starting any of these treatments.
It also proposed that a warning be included in the drug information leaflet.
The drugs, a new class known as "direct-acting antivirals" are more effective than their predecessors.
At a cost of some 40,000 to 80,000 euros ($43,000-$86,000) for a 12-week course, they are the preserve of a lucky few.
Hepatitis is an inflammation of the liver, most often caused by a virus but sometimes by drug or alcohol abuse, other infections, or autoimmune diseases.
The B and C types usually occur from contact with body fluids of an infected person. Other than for hepatitis B, there is no vaccine against hepatitis C.
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