Key Walgreen revenue metric falls 6.1 pct in Dec.

The Deerfield, Ill., company said Friday revenue from stores open at least a year dropped 6.1 percent last month as a shift toward generic drugs and a calendar quirk hurt the company's sales. Pharmacy revenue tumbled 8.9 percent, while revenue from the front end, or rest of the store fell, 2.3 percent.

Revenue from stores open at least a year is considered a key indicator of retailer health because it leaves out results from locations that have opened or closed in the last year.

Analysts expected, on average, an overall decrease of 5.2 percent, according to Thomson Reuters. They expected a slightly larger than reported drop of 9 percent drop in pharmacy revenue coupled with a gain of less than 1 percent from the front end.

Walgreen runs more than 8,000 drugstores.

Walgreen said a calendar shift that added one Sunday and Monday to last month while taking away a Thursday and Friday, compared to December 2011, affected results. Drugstores typically get more business during weekdays when customers are more likely to see a doctor and then fill a prescription.

The company said customer traffic fell 4 percent in stores open at least a year.