State health officials don't know how often Marylanders use medications mixed in facilities lacking safety oversight, like a Massachusetts facility linked to three deaths here, but a newly passed law could tell them — and help demonstrate a gap in federal regulation. Batches of sterile drugs from so-called compounding pharmacies will be subject to state review under the measure Gov. Martin O'Malley signed this month. And pharmacists and doctors who perform compounding, in which drugs are somehow altered from their Food and Drug Administration-approved form, will face an extra layer of permits and inspections for drugs used in Maryland. But "it's not realistic for Maryland to set up national oversight," said Joshua M. Sharfstein, the state health secretary.