KANSAS CITY, Mo. -- Pharmacist Robert R. Courtney watered down drugs for the past decade, possibly affecting 4,200 patients, federal authorities said Friday.

The U.S. Attorney's Office said Courtney now admits diluting drugs on a far larger scale than at the time of his guilty plea in February.

When Courtney confessed in August 2001, he acknowledged diluting four chemotherapy drugs involving 34 patients. The new revelations multiply the potential victims and involve more than 60 drugs.

Federal authorities said they are working to notify potential victims.

Courtney's plea agreement called for him to tell federal investigators about his drug dilutions. The revelations about the number of victims have come in debriefings since his February plea.

The U.S. Attorney's office said all of the drugs Courtney claims were diluted were administered intravenously or through injections. None of the drugs Courtney claims were diluted were oral medications or dispensed in pill or tablet form.

Federal prosecutors acknowledged their "inability to conclusively confirm Courtney's additional dilution claims," but said they were working with federal and state officials to notify potential victims. Authorities believe Courtney diluted 98,000 prescriptions, issued through about 400 doctors, potentially affecting about 4,200 patients.

State agencies in Kansas and Missouri on Wednesday received the information they need to begin notifying doctors who may have been affected by the dilutions.

Courtney, 49, pleaded guilty to 20 federal counts of tampering and adulterating or misbranding the chemotherapy drugs Taxol and Gemzar. He admitted then to diluting medications 158 times for 34 patients.

The druggist also faces a fine of up to $15 million. No sentencing date has been set. His plea agreement calls for prosecutors to recommend a sentence of 17 1/2 to 30 years, far less than the 196-year maximum.

Courtney wrote in an earlier confession that he was motivated by a need for money, including a $600,000 tax liability.