Hajara survived the trials but cannot now hear or speak

Pfizer lawyers argued in Abuja that the amendments had been improperly filed.

The Nigerian government wants $7bn in damages and compensation for the families of the children who died or suffered serious side-effects.

Some 200 children took part in trials for a new anti-meningitis drug in 1996. Pfizer says the trials were lawful.

The court rejected a bid by the Nigerian government's counsel to include 85 new claims - in addition to an earlier 54, agreeing with Pfizer that it had been improperly filed.

Officials in Kano say more than 50 children died in the experiment, while many others developed mental and physical deformities.

But Pfizer says only 11 of the 200 children in the drug trial died.

We did not suspect that the children were being used for an experiment

Hassan Sani

Family anger over trials

Pfizer tested the then unregistered drug in Nigeria's north-western Kano State during an outbreak of meningitis which had affected thousands of children.

Following pressure, the Nigerian government set up an expert medical panel to review the drug trial.

It concluded that the experiment was "an illegal trial of an unregistered drug" and a "clear case of exploitation of the ignorant".

"We did not suspect that the children were being used for an experiment," Hassan Sani, the father of a girl who was tested, told the BBC in Kano recently.

"The American doctors took advantage of our illiteracy and cheated us and our children. We thought they were helping us," he said.

Pfizer denied any wrongdoing and said its trial of Trovan was conducted in accordance with Nigerian regulations.

The Pfizer experiment was cited by many as a reason for the mass rejection of polio vaccinations in many parts of northern Nigeria in recent years.