Philadelphia ? In the wake of more than 400 deaths nationwide from heroin laced with the painkiller fentanyl, some needle exchange programs are giving addicts prescriptions for a drug to keep on hand to halt an overdose.

The antidote – naloxone, which is sold under the brand name Narcan – can save the life of someone who might not call 911 for fear of prosecution, treatment providers say.

Even if a user does call, help can arrive too late.

“If people have to rely on paramedics, more often than not, the overdose is going to be fatal, just because of the amount of time for people to get there,” said Casey Cook, executive director of Prevention Point Philadelphia, a nonprofit that runs the city’s needle exchange program. The group recently began distributing naloxone prescriptions through a physician.

But others say naloxone is best administered by trained paramedics and that the prescription approach might appear to condone drug use.

Fentanyl – an opiate used legally in anesthesia and for some cancer patients – is cheaper than heroin and 80 times more potent than morphine. That makes it an appealing additive for heroin distributors.

At least 150 fentanyl deaths have been recorded in the Philadelphia area, 130 in Chicago and 130 in Detroit.