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Shares of Walgreen Co. hit a 52-week high in intraday trading Wednesday after the company reported same store sales that beat Wall Street’s expectations for the fourth month in a row.

The Deerfield-based company said sales in stores open at least year grew by 4.4 percent last month due in part to pharmacy sales, which were up nearly 8 percent last month compared to the previous year.

Overall, May sales were up 6 percent to $6.57 billion compared to May 2013. Pharmacy sales accounted for 64.2 percent of total sales for the month of May.

Wall Street was expecting a same stores sales increase of 4.2 percent according to analytics firm RetailMetrics.

Walgreens, the nation’s leading drug store chain, is coming off its biggest monthly same-store sales increase in seven years. Last month, it reported a jump of 7.6 percent, according to Ken Perkins, president of Retail Metrics.

Sales in stores open at least a year are a key gauge of retailers’ health and strip the volatility that comes with stores opening and closing in any given month.

Prescriptions filled at stores open at least a year were up 3.5 percent last month, compared to May 2013, Walgreens said. Prescriptions filled were lower than expected, the company said, due to calendar shifts.

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WAG data by YCharts