Europe's drug safety regulator said multiple sclerosis treatments known as interferon beta need stronger label warnings because some patients treated with the drugs have suffered side effects affecting the kidney and other organs.
A spokeswoman for the European Medicines Agency said the label change would affect all countries in the European Union.
In a statement posted on its website on Wednesday, German regulator BfArM said cases of a condition called thrombotic microangiopathy, or TMA, have occurred after weeks or even several years of treatment with interferon beta, some of them fatal.
Neither agency said how many patients could be affected.
The drugs in question are Biogen Idec's Avonex and Plegridy drugs, Merck KGaA's Rebif, Bayer's Betaferon and Novartis's Extavia.
Interferon beta drugs, which are injected, have been in use for more than 10 years.
TMA affects the kidney and a range of other organs, and BfArM said its symptoms included high blood pressure, fever, disorientation, impaired kidney function and a low count of coagulation cells in the blood.
It added that patients diagnosed with TMA should be taken off interferon beta and should be treated immediately.
Cases of another condition, nephrotic syndrome, have also been reported among interferon beta users and will be included in the label change, the European and German regulators said, again without saying how many patients could be affected.