COLUMBUS, Ohio (AP) -- A drug used to sedate elephants and other large animals, 100 times as potent as the fentanyl already escalating the country's heroin troubles, is suspected in spates of overdoses in several states, where authorities say they've found it mixed with or passed off as heroin.

The appearance of carfentanil, one of the most potent opioids known to investigators, adds another twist to the fight against painkillers in a country already awash in heroin and fentanyl cases.

"It certainly is a very disturbing trend," Ohio Attorney General Mike DeWine said.

A man suspected of selling carfentanil as heroin was indicted this week in central Ohio on 20 counts, including murder, in connection with a July 10 death and nine other overdoses that happened within hours of one another. The suspect, 36-year-old Rayshon Alexander, pleaded not guilty.

Investigators are still trying to track down the source of the carfentanil. DeWine said he wasn't aware of any thefts of the drug, which, he noted, could be shipped from abroad or produced here.

The drug has been suspected in overdoses or found in seized drugs in central Kentucky and in Florida's Tampa Bay and Sarasota areas, as well as other Ohio cities. Akron authorities have seen over 230 overdoses in July, 20 of them fatal, and police said evidence of carfentanil was found in some of those.

Carfentanil is thought to be similar in strength to a painkiller known as W-18, which has shown up in heroin in Philadelphia, New England and Canada. Such drugs up the ante in a market where sellers already mix powerful painkillers with or disguise them as heroin to increase their products' potency, which can increase overdose risks for users chasing more intense highs, especially when they're not aware of what they're actually using.

Carfentanil is so powerful that zoo veterinarians typically wear a face shield, gloves and other protective gear -- "just a little bit short of a hazmat suit" -- when preparing the medicine to sedate animals because even one drop splattered into a person's eye or nose could be fatal, said Dr. Rob Hilsenroth, executive director of the American Association of Zoo Veterinarians.

In some suspected carfentanil cases, emergency responders have had to administer multiple doses of the overdose antidote naloxone -- often known by the brand name Narcan -- to save people, but even the antidote might not be enough.

Dr. Lakshmi Sammarco, the Hamilton County coroner in Cincinnati, publicly warned users during a recent news conference: "Narcan may not save you on this one."