MANILA, Philippines -- The National Bureau of Investigation (NBI) has filed charges against eight people allegedly engaged in selling and distribution in Sta. Cruz Manila of counterfeit anti-impotency drug Viagra.

Charges for violation of Republic Act 8203 or the Special Law on Counterfeit Drugs were filed by the NBI against Patricia Cua, Shirley Ong, Helen Wang, Aileen Cua, Sherleen Cua, Lisa Hernandez and Saidali Ampaso before the Manila Prosecutor's Office.

Of the seven suspects, only Hernandez, drugstore employee, and Ampaso, alleged drug peddler, were arrested. The five others, said to be owners of Shun Cheng Tong Chinese Drugstore on Ronquillo Street, Sta, Cruz, remain at large.

Lawyer Allan Contado, chief of the NBI Anti-Graft Division, said the filing of charges stemmed from the complaint filed by lawyer Abelaine Alcantara, representative of Pfizer Inc., the exclusive distributor of Viagra.

Investigation showed that last January, Ricky Taguding of Hills and Associates, a market researcher for Pfizer, reported the sale by several persons of counterfeit Viagra, particularly along Rizal Avenue within the vicinity of Carriedo, Sta. Cruz.

This prompted Pfizer to file a complaint against owners and employees of the drugstore at the NBI, which immediately set up an entrapment operation.

Suspect Ampaso was arrested last week after handing out 20 boxes of Viagra in exchange for the marked money from an NBI agent who pretended as a buyer.

The bureau agents, armed with search warrants issued by Manila regional trial court Judge Virgilio Almeda, then swooped down on the drugstore where they arrested Hernandez.

Seized from the establishment were several boxes of Viagra worth P115,000.

The counterfeit Viagra was sold at P700 to P1,000 per box, lower than the original Viagra's actual market price of P1,600 per box, the NBI said.

The Bureau of Food and Drugs and Pfizer have issued certifications indicating that the Viagra seized from the Chinese drugstore were fake.