A Boston federal magistrate judge has ruled that Amphastar Pharmaceuticals Inc. must pay opponent Momenta Pharmaceuticals Inc.’s legal fees in a dispute over Amphastar’s failure to produce court-ordered documents.

However, U.S. District Magistrate Judge Robert Collings stopped short of non-monetary sanctions. Although Amphastar’s violations “were quite serious and possibly contumacious,” he said, they did not require case-related sanctions such as a ruling for the plaintiffs on a substantive issue.

“In the end, the Court does not see plaintiffs as having been substantially prejudiced in their presentation of their claims on account of Amphastar’s disobedience of the Court’s Orders,” Collings wrote.

Momenta and license partner Sandoz Inc. sued Amphastar, subsidiary International Medication Systems Ltd. and distribution and sales partner Watson Pharmaceutical Inc. in September 2011.

The plaintiffs claimed that Amphastar’s quality-control testing infringed its patent for analyzing enoxaparin, the generic version of blood clot prevention drug Lovenox. The sanctions order followed two June 2012 court orders that Amphastar produce certain documents.

One of those orders required Amphastar to produce unredacted copies of all redacted documents it previously had given to the plaintiffs. Another required Amphastar to produce a complete copy of all amendments to its U.S. Food and Drug Administration abbreviated new drug application to sell a generic enoxaparin drug in the United States.

The case was stayed for about six months following an August 2012 U.S. Court of Appeals for the Federal Circuit ruling overturning a preliminary injunction against Amphastar.

This July, U.S. District Judge Nathaniel Gorton in Boston granted a summary judgment to Amphastar and other defendants on the ground that the FDA’s safe harbor for activities related to Abbreviated New Drug Application submissions protected its actions from infringement allegations.

Momenta’s lawyers at Boston’s Choate Hall & Stewart declined to comment. Sandoz’s lawyers at McDermott, Will & Emery, did not respond to requests for comment. Amphastar and its lawyers at K&L Gates also did not respond.

The ruling is “a caution to litigants, to the lawyers and to the clients that when there are document production issues you need to really be on top of them,” and not to misrepresent what’s going on to the court, said Erik Belt, an intellectual property partner in the Boston office of McCarter & English, who wasn’t involved in the case.

Sheri Qualters can be contacted at squalters@alm.com.