BOSTON — Restrictions on the potent new painkiller Zohydro are within the Massachusetts' right to regulate the dispensing of prescription drugs, state officials argued in a legal brief filed Wednesday in a federal lawsuit challenging the rules' constitutionality.Gov. Deval Patrick, Public Health Commissioner Cheryl Bartlett and members of the state Board of Registration in Medicine maintained that the restrictions do not impose "anything close" to an "effective ban" on the drug, as its manufacturer, Zogenix, claims in a lawsuit filed last month.