NEW YORK (Reuters Health) Feb 13 - Pfizer said on Monday that it has halted a late-stage clinical trial of the investigational neuropathic pain drug pregabalin due to US regulators' concern about tumors in mice given the drug.
Pfizer has been developing pregabalin as a successor to its anticonvulsant medicine Neurontin, which boasted fourth-quarter sales of $371 million but is facing the possible loss of its US marketing exclusivity.
Company spokesman Andrew McCormick said in an interview that the phase III trial was put on "clinical hold" after the US Food and Drug Administration (FDA) became concerned about the fact that mice given the drug developed a higher incidence of a type of tumor.
Pfizer said investigators are still unsure whether the increased risk of tumors seen in mice taking pregabalin would be applicable to humans.
But Mara Goldstein, a drug analyst for CIBC World Markets, said Pfizer's announcement about the mice tumors is cause for concern. "You always have to sit up and take notice when a drug company has to restrict a patient population in a clinical trial and any time a trial is halted for any reason," Goldstein said.
McCormick would not speculate on whether the FDA would want other pregabalin trials to be halted. The drug is also being tested for epilepsy, a variety of anxiety disorders and chronic pain.
"We're continuing our discussions with the FDA on the other indications," McCormick said.
The FDA has stipulated that any future patients enrolled in trials of pregabalin for neuropathic pain — pain caused by nerve — damage "need to have failed standard therapy," he noted. Previously, the drug's neuropathic pain trials did not have such a restriction, but allowed enrollment of patients taking the drug as first-line treatment.
Despite the FDA's concerns, McCormick said Pfizer intends to proceed with plans to seek US marketing approval of pregabalin for neuropathic pain and epilepsy in the second half of 2001, based on separate earlier trials of the medicine.
"We have said previously we would file for marketing approval by then, and we're sticking to that," the spokesman said. He said Pfizer would also ask the FDA in 2001 to approve Neurontin for neuropathic pain.
CIBC's Goldstein said she was already somewhat concerned about the safety of pregabalin after her firm conducted earlier independent inquiries "that came up with some possible issues of toxicity in humans." She declined to be more specific.
But Goldstein said it would be premature to assume that the mouse tumors would derail pregabalin's chances of winning FDA marketing approval.
"To be fair, I can
think of other cases where animal studies have revealed some type of toxicity
in a drug, but which later were found not to be an issue in humans," she
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