BOSTON (AP) -- Massachusetts must temporarily suspend one of its key restrictions on Zohydro, a powerful new prescription painkiller, pending the outcome of a lawsuit challenging their constitutionality, a federal judge ruled Tuesday.

U.S. District Court Judge Rya Zobel ordered the state to stop requiring doctors and other prescribers to issue a so-called "letter of medical necessity" stating that "other pain management treatments have failed" before prescribing the hydrocodone-based drug.

But the judge allowed the state to continue to require that only pharmacists -- not pharmacy technicians or other staffers -- handle or dispense the drug, which comes in higher doses than Vicodin and other comparable drugs and can be easily abused, according to public health officials.

Zobel also denied the state's request to dismiss outright a lawsuit filed by Zogenix, the San Diego-based maker of the drug.

The regulations were imposed in late April and early May as Gov. Deval Patrick sought to tackle a "public health emergency" around drug abuse and overdoses.

Zogenix argues the restrictions are unconstitutional because they represent a "de-facto ban" on a painkiller already approved by the U.S. Food and Drug Administration for use in cases of severe and chronic pain. The state maintains it has the right to regulate the medical and pharmacy professions within its borders.