Ten Connecticut prescribers, including a Derby nurse who is at the center of a federal kickback probe, were responsible for more than 23 percent of the state’s Medicare spending on opioids in 2014, suggesting that the largest share of those prescriptions is concentrated among a small number of clinicians. Recently released federal Medicare data show that Heather Alfonso, formerly a nurse with the Comprehensive Pain & Headache Treatment Centers, LLC, in Derby, and four other advanced practice registered nurses (APRNs) at the clinic in 2014 dispensed more than $8.4 million in opioids in the Medicare program – accounting for a full 15 percent of all such prescriptions in the state. They were among the top 10 opioid prescribers in 2014, who accounted for $13 million of the $56 million spent on the drugs, the data show. More than 4,800 Connecticut clinicians, mostly physicians, wrote Medicare prescriptions for oxycodone, fentanyl and other opioids. But the prescribing was not evenly spread out – only two-dozen prescribers wrote out more than $250,000 worth of prescriptions.