State health officials declared Dr. Mark Kantzler unfit to practice medicine because of drug abuse and, fearing for his patients' safety, suspended his license by emergency order in July 1991.

Today, the family practitioner runs a St. Petersburg area pain clinic . He is among Florida's top prescribers of narcotics to low-income people -- $419,751 worth in the past three years. During that time, eight of his patients have died of drug overdoses.

A South Florida Sun-Sentinel investigation found dozens of doctors allowed to continue freely prescribing dangerous drugs at state expense, even after multiple patients have died of an overdose, and even in extreme cases where they have been charged with drug crimes or serious misconduct. The state has no system that monitors, sounds an alarm or stops doctors who abuse the system.

The investigation found:

As a group, the doctors who prescribe the most narcotics to Medicaid patients are 10 times more likely to have troubled professional histories than doctors overall in the state.

State officials have disciplined or charged 10 of the top 200 Medicaid-prescribing doctors for abusing drugs, trading pills for sex with patients, or recklessly handing out prescriptions. At least another 15 have faced criminal charges ranging from insurance billing fraud to drug trafficking, or have been accused by state regulators of incompetence or misconduct.

Doctors who prescribed the costliest volumes of drugs have some of the shakiest practice records. And doctors who prescribe the largest amounts of OxyContin, an often-abused painkiller, have the highest rate of disciplinary problems.

Seven of 16 doctors who each wrote more than $1 million worth of narcotics prescriptions had professional misconduct charges or criminal arrests in their pasts, including two doctors arrested for narcotics trafficking. Nine of 29 doctors who ordered OxyContin for 100 or more Medicaid patients last year had serious disciplinary action or arrests in their pasts.

No state agency has set up a system to monitor the practices of troubled doctors whose patients wind up dying of pill overdoses. Even when investigations have been opened, they took years to complete and the doctors continued to see patients and to hand out prescriptions.

No alerts in place

The Sun-Sentinel traced hundreds of overdose deaths through autopsy records collected from Florida's two dozen medical examiners and through pharmacy billing data to many of the top Medicaid-prescribing doctors.

In some cases, doctors who dramatically increased the number of those prescriptions experienced a rash of deaths among their patients. State officials concede that they have no system that alerts them to spikes in a doctor's Medicaid billings for narcotics or to numerous deaths among a doctor's patients.

Medicaid's costs for Kantzler's prescriptions nearly doubled in 2001 and into 2002, when he wrote more controlled-drug orders than all but 79 of almost 57,000 Florida medical professionals.

During that time, six of his patients died of overdoses.

Two men in their late 40s died in March 2001, one from codeine and the other from the painkiller hydrocodone and a muscle relaxant, records show. In August of that year, a man died of "acute hydrocodone toxicity" a day after he filled a prescription for the drug from Kantzler. Then, in December, a 42-year-old female patient mixed pills with cocaine and died, autopsy records show.

Kantzler's personal problems with drugs go back a decade.

Starting in late 1989, he spent six months hospitalized in a rehabilitation program for drug abuse. About a year later, a urine screen found Nubain, a morphine-like drug, in his system, and the state suspended his license.

Florida's Board of Osteopathic Medicine gave it back two months later after a psychologist said Kantzler could safely return to practice as long as he kept up counseling and submitted to random urine screens.

Kantzler, without admitting he did anything wrong, agreed to pay a $2,500 fine and complete a course of drug rehabilitation. He could not be reached for comment for this story after repeated phone calls and a letter sent to his office. Kantzler is one of a small number of doctors who stand out for writing high volumes of prescriptions, according to the newspaper's analysis of Medicaid billing records.