HOUSTON -- A doctor and several clinic owners have been accused of illegally distributing pills, KPRC Local 2 reported Friday.

Investigators said they were tipped off while looking into a fire at the Uptown Medical Clinic, at 7231 FM 1960 in Humble, on Jan. 23.

Officials said thousands of pain pills were illegally prescribed to patients by a doctor and non-licensed personnel working at the clinic.

"Once you boil it down, it was a drug-dealer operating behind a medical license," said Dustin Deutsch, a senior investigator with the Harris County Fire Mashal's Office.

Five people were charged with engaging in organized criminal activity, including Dr. Christina Clardy, clinic owner Tawny Hughes, Brandon Harris and Wilfredo Duran.

Duran is also charged with practicing medicine without a license.

Investigators said Hardy was one of the top 10 pain pill-prescribing doctors in the state of Texas. In 2009, she prescribed 2.9 million tablets of Vicodin, Xanax and Soma.

Officials said they also found $37,800 cash, as well as pre-signed prescription pads, at her home and office.

Investigators said Bush Airport Medical Clinic is now known as Uptown Medical Clinic. Some of the suspects also worked at Texas Medical Direct.

Both clinics have been shut down.

Clardy surrendered her DEA number and her authority to write prescriptions as a result of the investigation.

The Harris County Fire Marshals Office is working on the case along with the District Attorney's Office and the U.S. Drug Enforcement Agency.

Officials are also looking into a physician's assistant who may be connected with the case.