TeGenero, the drug firm which manufactured the medication which left six men seriously ill in a London hospital, has confirmed the drug showed negative side effects when tested on animals.
The German company said two monkeys injected with the drug in a pre-clinical trial experienced temporary swelling in the glands.
However, the company said the monkeys' symptoms were completely different from those suffered by the men tested last week.
Doctors say the condition of four of the men is continuing to improve after almost a week in intensive care.
