The FDA, working with international regulatory and law enforcement agencies from about 100 countries, said on Thursday that it took action against more than 4,100 Internet pharmacies, bringing civil and criminal charges, removing offending websites and seizing drugs worldwide.

The move was part of the fifth annual International Internet Week of Action, a global effort to fight the online sale and distribution of potentially counterfeit and illegal medicine.

Action taken between September 25 and October 2 resulted in the shutdown of more than 18,000 illegal pharmacy websites and the seizure of 3.7 million doses of counterfeit medicines worth an estimated $10.5 million, the agency said.

Homeland Security Investigations, which took part in the coordinated effort titled Pangea, said preliminary results show the actions also accounted for 79 arrests.

"Consumers in the United States and around the world face a real threat from Internet pharmacies that illegally sell potentially substandard, counterfeit, adulterated or otherwise unsafe medicines," FDA Commissioner Margaret Hamburg said in a statement.

"This week's efforts show that strong international enforcement efforts are required to combat this global public health problem," she added.

Among the targeted online pharmacies was Canadadrugs, which earlier this year had been a subject of the investigation into fake versions of the cancer drug Avastin that found their way into U.S. oncology clinics. Canadadrugs denied any connection to the counterfeit Avastin.

An FDA warning letter obtained by Reuters accused Canadadrugs of selling drugs for unapproved uses and medicines made by unapproved manufacturers, among other infractions.

Warning letters to other online pharmacies cited the sale of "female Viagra," which does not exist, and unapproved variations on well-known erectile dysfunction drugs with names like "Viagra Professional" and "Cialis Super Active."

The goal of the annual effort, which involved law enforcement, customs and regulatory authorities from 100 countries, was to identify producers and distributors of illegal pharmaceutical products and medical devices and remove these products from the supply chain.

The FDA said it targeted websites selling potentially dangerous medicines, including those with active ingredients approved by FDA for use only under the supervision of a licensed health care practitioner or containing active ingredients that had been withdrawn from U.S. markets due to safety issues.

In addition to Tamiflu and Viagra, the agency targeted sales of domperidone, which was removed from the U.S. market in 1998 because it may cause serious heart problems or death, and isotretinoin, previously marketed in the United States as the acne treatment Accutane, which has been liked to birth defects.

The FDA is working with its foreign counterparts to address the remaining websites that continue to offer unapproved or misbranded prescription medicines to U.S. consumers, the agency said.

(Reporting By Debra Sherman in Chicago and Bill Berkrot in New York; Editing by Maureen Bavdek, Bernard Orr)

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