PHILADELPHIA — Gov. Tom Corbett signed a bill Tuesday that supporters say will reduce the number of fatal heroin overdoses in part by making an antidote more available to police and the public.

The legislation also offers immunity from criminal prosecution to those who help overdose victims. The law will take effect in 60 days.

A legislative study found deadly drug overdoses skyrocketed in the state between 1990 and 2011. Experts say the increase is due in large part to the abuse of legal painkillers called opioids, whose users switch to heroin when their prescriptions run out or become too expensive.

Rural overdose deaths increased from about one per 100,000 residents to 13 per 100,000. Urban fatalities rose from about three to 16 per 100,000 residents.

A drug called naloxone, commonly referred to by the brand name Narcan, reverses the effects of heroin and opioids like oxycodone. Although Pennsylvania permits paramedics and doctors to use it, police were not able to legally administer the antidote until now.