Pfizer (NYSE:PFE) is following in the footsteps of supermarkets like Kroger (NYSE:KR) and Safeway (NYSE:SWY). The Financial Times reports that the drugmaker is expanding its offering of discount cards as a way to track whether patients with chronic diseases are refilling their medications.

What's next? Maybe Lowe's (NYSE:LOW) and Home Depot (NYSE:HD) should set up discount cards to remind customers to track how often they change the filter in their furnace. Or maybe dry cleaners will start calling you to remind you to bring in your clothes.

Don't get me wrong: Filling prescriptions regularly will make most patients healthier, but this is a slippery slope for drugmakers. They have generally taken a hands-off approach to dealing with patients. Even direct-to-consumer advertisements require a doctor to get involved. While insurance companies like Cigna (NYSE:CI) or pharmacies like CVS Caremark (NYSE:CVS) may call to remind patients to refill their prescriptions -- both have my household on speed dial -- there's a perceived difference when the one pushing the pills is the "big bad drugmaker." We're talking about health data, after all, not how often you buy milk.

That may be why Pfizer is expanding the use of discount cards into countries like Russia, Mexico, Brazil, and Venezuela. Without insurance for prescription medications, many patients pay out of pocket, so a substantial discount may be worth giving up some privacy.

Pfizer and other drug companies like GlaxoSmithKline that have moved heavily into markets like these need high volumes to make up for the lower prices that patients in these countries are able to pay. The discount cards should help keep the volume high, and if Pfizer has taken a cue from supermarkets, the discount is off an already inflated price.

But Pfizer should be careful with expanding the practice further, especially into the U.S. I'm not sure Americans will be as willing to have their drug refills tracked by those making a buck off them.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Home Depot, Lowe's, and Pfizer are Inside Value recommendations. The Fool owns shares of GlaxoSmithKline. The Fool has a disclosure policy.