A new longer-lasting version of the drugmaker’s antipsychotic appears effective, but a small number of patients experienced excessive sleepiness, according to FDA medical reviewers, who posted a briefing document on the agency’s web site in advance of an advisory committee meeting on Wednesday.

Zyprexa, of course, is currently marketed as a once-daily pill to treat schizophrenia and bipolar disorder, while the new formulation is injected into the muscle and is designed to last two to four weeks. But the FDA reviewers plan to ask the Psychopharmalogic Drugs Advisory commitee to assess cases of “profound sedation,” which was seen in 1.2 percent of patients. Most occurred within three hours after injection, by the way.

According to FDA, the side effect is unique to the injectable version of Zyprexa and may require a warning labeling. Based on draft questions posted to its Web site, FDA will ask its advisers whether the drug requires a Black Box warning (see pages 1 and 2 of the briefing document). (The pill is linked to weight gain and diabetes, which prompted Lilly has so far paid $1.2 billion to settle 30,000 lawsuits, and may pay a $1 billion fine for off-label marketing violations).

In its own documents, Lilly argues that the unusual side effect is found in both the pill and the new injectable version. Look on page 56 where it says there were “no differences in the incidence or timing of sedation” events between old and new forms of Zyprexa. In explaining the sedation, the drugmaker suggests the side effects may have been due to docs incorrectly injecting Zyprexa directly into the bloodstream, instead of into the muscle, because absorption takes place in just a few hours instead of days or more.