But the Nigerian government says Pfizer administered Trovan without authorisation or parental consent among children at a field hospital during an outbreak of measles, cholera and meningitis in Kano.

"In the midst of the epidemic, Pfizer devised a scheme under which it misrepresented and failed to disclose its primary motive in seeking to participate in giving care to the victims of the epidemic," the federal lawsuit says.

Child deaths

Eleven children died during the trial while many more - reportedly 181 - suffered from deafness, paralysis, brain damage and blindness,  according to the allegations.

The regional government in Kano, Nigeria's largest state, has also filed a lawsuit against the company seeking more than $2bn.

Pletan said that Trovan was in the final phase of trials at the time, having been previously tested on 5,000 volunteers in Europe, the United States and Japan. Their evidence was that the drug could be used to help treat the meningitis emergency.

Contrary to charges that the Nigerian tests had been conducted under the guise of humanitarian aid, the programme was "completely  transparent" and in line with US and European standards for drug evaluations, he said.

Bilingual nurses informed the parents of the children enrolled in the trial in both English and Hausa, the local language, and the parents gave their consent, Pfizer said in an earlier statement.

The US Food and Drug Administration (FDA) cleared Trovan for adult use in 1997 and the drug swiftly became established as one of the most prescribed antibiotics in the US market.

It was later associated with reports of liver damage and deaths,  prompting the FDA in 1999 to restrict its use to serious adult cases.

That same year, European drug regulators recommended its suspension from the European market, a decision that has been made permanent, according to the Pfizer website.