Local police are warning that an extremely powerful and potentially fatal batch of drugs, being sold as heroin, has hit the Buffalo area.

Laboratory tests confirmed that one of two batches of heroin recently purchased by undercover lawmen from a Buffalo drug trafficker was not heroin but a highly potent and very dangerous drug routinely given to severely ailing cancer patients, Erie County Sheriff Timothy Howard and Buffalo Police Detective Chief Dennis J. Richards reported.

Police issued the alert hours after the arrest on Niagara Street of Angel Marcial and a search of his Arthur Street home.

They made a public plea to anyone who may have purchased heroin from Marcial, as well as other heroin users, to avoid recent purchases.

Tests completed Friday showed that one of the two batches of heroin undercover deputies purchased from Marcial confirmed that the batch was 100-percent fentanyl with no heroin, police said.

Street dealers sometimes lace their heroin with fentanyl to make for a “hot dose,” giving the user more of an immediate high, said Alan Rozansky, head of the sheriff’s Narcotics Bureau. But street dealers can be clumsy about their dosings.

Marcial, who has an extensive criminal record and was free on bail stemming from his latest drug arrest in January, was tackled by Buffalo Police Lt. Sheila Wiles as he tried to run from police officers and sheriff’s detectives when confronted at a gas station in the 2200 block of Niagara at 3:20 p.m. Friday.

A search of Marcial’s Arthur Street home led to the seizure of $4,600 cash and about 20 grams of suspected heroin, a loaded 45-caliber semi-automatic pistol and a police scanner tuned to Buffalo Police radio channels.

Central Police Services Lab has not yet completed the testing of the second of the two batches of alleged heroin.