The world's largest maker of HIV/AIDS drugs, GlaxoSmithKline Plc, suffers a setback in the development of a new kind of AIDS medication. Two cases of serious liver problems have been reported in patients taking its experimental drug Aplaviroc, causing the company to stop further testing.

Phase III tests of the product on patients who have not received other HIV therapies has ended.

Aplaviroc, or GSK 873140, belongs to a new class of oral medicines called CCR5 inhibitors that can block the AIDS virus before it enters human cells.

The discovery of severe liver toxicity is a setback for the drug, but does not mean the end research and development. Glaxo is offering treatment-experienced patients the option of continuing in its Phase III study, but with additional monitoring for liver toxicity.

A Glaxo spokesman tells Reuters