Drug giant Pfizer has been issued with an official warning letter by US regulators after “significant violations” resulted in overdoses being administered to several children enrolled in one of its clinical trials

In a letter dated 9 April and released yesterday, the Food and Drug Administration says an investigation has found the company failed to properly oversee the trial. “As a result of inadequate monitoring, widespread overdosing of study subjects at multiple study sites was neither detected nor corrected in a timely manner,” the letter says.

This is not the first time this trial has come under scrutiny. The FDA’s letter notes that failing to ensure proper monitoring “is a repeat violation” of problems flagged in a 2005 investigation.

Although the FDA redacted information on the drug involved from its letter, it is widely reported to be Geodon, an antipsychotic used to treat bipolar disorder and schizophrenia in adults. Pfizer says the problems cited in the letter were originally raised by its own staff years ago and it will soon provide new processes to prevent any recurrence of the problems identified (AP).

An FDA panel last June backed the use of Geodon in children suffering from bipolar disorder, although with some concerns expressed about the amount of evidence available to make a decision and the use of such powerful drugs in children in general (MSNBC, USA Today). Pfizer has also agreed to pay $2.3 billion to settle allegations of improper marketing of drugs including Geodon, says the Dow Jones Newswire.