CALGARY, Alberta – A few months ago, Dave Robertson had eight employees in the 800-square-foot office of his new Internet pharmacy business.

Today, Robertson’s crossborderpharmacy.com has 150 workers and 20,000 square feet of office space, serving an ever-expanding customer base that he says numbers close to 100,000 – nearly all of them U.S. consumers seeking cheaper Canadian medicine.

Scores of new, rapidly growing Canadian operations are filling prescriptions sent from south of the border, capitalizing on the disparity of drug prices between the North American neighbors.

The business worries pharmaceutical giants such as GlaxoSmithKline Inc., which wants to shut down operations like Robertson’s. Drug makers, as well as regulators, say they worry about the proper medical supervision and quality controls.

Canada regulates drug prices as part of its national health care system, while the market dictates pricing in the United States. Many popular medications for chronic conditions such as high blood pressure and high cholesterol can be bought in Canada at less than half the U.S. price.

Rough estimates put the number of Canadian companies in the business at 80 or more, and total annual revenues are believed to be as high as $650 million. Precise figures are unavailable because the companies are privately held and the situation changes daily.

Just ask Robertson, 39, a pharmacist who designed industry software until realizing the potential of reaching a U.S. market of aging citizens with diminishing medical insurance benefits and coverage.

He started crossborderpharmacy.com last fall in Calgary, and it has blossomed into separate departments for receiving telephone and Internet queries, filing information, consulting with U.S. doctors and patients, and filling and shipping orders.

Lower Canadian drug prices have attracted U.S. customers for years, with busloads of senior citizens from communities near the border making weekend trips to Canada to stock up.

Manitoba pharmacists were the first to market by Internet, extending service far beyond bordering states. Ronald Guse, registrar of the Manitoba Pharmaceutical Association, said Wednesday the latest figures indicate there are about 40 such operations in the province.

The flow of drugs to the United States is raising the potential for problems in supply to Canadians, Guse said. A rural hospital lost its pharmacist to one of the new operations, creating a vacancy difficult to fill, he said.

Guse’s association is studying possible guidelines for prescriptions to make sure they are valid under Canadian regulations.

Some provinces, including Manitoba, require doctors writing prescriptions to personally consult with patients, and Guse questioned how that can be done by a physician handling hundreds of prescriptions a day.

At crossborderpharmacy.

com, there are five or more pharmacists on duty at any one time to oversee prescriptions, and the company tries to contact every customer by phone, Robertson said.

GlaxoSmithKline, citing concerns about proper medical supervision, has told the Canadian wholesalers and retailers it supplies that they must provide assurances they are not selling drugs to the United States. If they don’t, Glaxo will stop supplying them.

It originally set a Jan. 21 deadline for complying but backed off Tuesday, saying it was working on a plan to ensure that customers still get enough drugs for Canadian consumers.

In response, Canadian pharmacies have banded together in associations and threatened lawsuits alleging unfair practices and trade violations. They say the issue is not quality of care but the money that GlaxoSmithKline sees going to Canadian companies.