A powerful veterinary sedative called medetomidine was detected in two drug samples collected after the latest mass drug overdose that hit the city’s Penn North community this month, Baltimore City Health Commissioner Dr. Michelle Taylor said Wednesday.

The sedative is frequently mixed with the synthetic opioid fentanyl and can make overdoses harder to reverse. It appears to have infiltrated Maryland’s drug supply after it was linked to overdose clusters in Philadelphia last year.

A state testing program that looks at the composition of illicit drugs used on the street has infrequently found the sedative in its sampling of the city. But in sampling from Cecil County, which is closer to the Philadelphia region, the program has detected medetomidine in nearly 70% of the substances tested this year.

Taylor revealed the findings during a meeting of an advisory board charged with making recommendations on how to spend millions of dollars the city won from a lawsuit against opioid companies.

Medetomidine can be especially dangerous for people who use drugs because naloxone, a commonly used drug to treat opioid overdoses, is not effective against the tranquilizer.

The health department on Wednesday said it recommends providing rescue breathing and calling 911 if medetomidine is suspected in an overdose. Candy Kerr, spokesperson for the Baltimore Harm Reduction Coalition, agreed, saying the group had changed the way it recommends people respond to overdoses.

“It’s another additive that makes it harder for people who use drugs and people trying to save people who use drugs,” Kerr said.

Since July, the Penn North area has seen three mass overdoses, with the most recent occurring Oct. 8 and affecting 11 people. Dozens of people were hospitalized over the three events, but no one died. A Baltimore Police Department spokesperson on Wednesday said the investigation into the overdoses is ongoing.

Samples tested after the first mass overdose in July contained a different sedative called methylclonazepam.

Taylor said the health department is developing a mass overdose response protocol that is meant to coordinate fast and efficient emergency action.

“Between July 10 and Oct. 8, you can definitely tell that the coordinated response has improved greatly,” Taylor said.

But at least one community group leader has expressed disappointment with the city’s response and said more work is needed.

Anne Langley, executive director of Charm City Care Connection, a nonprofit that serves people who use illicit drugs, said the city did not alert her group about the mass overdose this month.

If it had known, she said, it could have helped canvass the area or warned clients to be careful of the drug supply.

“It’s hard to feel like we’re doing the best by our clients when we don’t have good information about what’s happening across the city,” Langley said.

Banner reporter Justin Fenton contributed to this article.