Montgomery County police arrested the owners of a Silver Spring pharmacy and two other men and charged them with distributing drugs illegally after a raid on the drugstore Tuesday.

Police said their investigation of the Silver Spring Professional Pharmacy at 808 Pershing Dr. began seven months ago after federal drug authorities reported that the small pharmacy was buying large quantities of the opium-based painkiller Dilaudin.

The drug is frequently used by drug addicts as a substitute for heroin.

Police alleged that pharmacist Barbara Ann Kirby, 32, and her husband Michael Oliver Kirby, 34, owners of the pharmacy, who live at 9347 Alcona St., Lanham, obtained the drugs from legitimate pharmaceutical suppliers and passed them on to Tyrone Curtis Parker, 38, a hair-salon owner who lives at 2466 Skylark Place SE.

Police said that Baltimore resident David Browning Jr., 33, was also arrested and charged with several drug offenses. All four were released on personal recognizance. None could be reached for comment yesterday.

Det. Fred Ailes said police monitoring shipments of Dilaudin found that the pharmacy had been ordering 1,000 tablets a month. Ailes said he checked with other pharmacies and came to the conclusion that 1,000 a month "was an excessive amount."

Through surveillance, he said, police found that the drug shipments were disappearing as soon as an hour after they arrived at the pharmacy. Surveillance in Montgomery and Prince George's counties and the District convinced police that Michael Kirby was handing the drugs over to a man driving a Mercedes-Benz registered to Parker, Ailes said.

The drug, frequently referred to as "D's," costs $300 for 1,000 tablets from a legitimate pharmaceutical wholesaler, but sells for between $35 and $60 a tablet when sold illegally on the street.