The country is getting older. Physicians and patients are increasingly turning to pharmaceuticals to solve problems. And customers are increasingly willing to conduct business through the mail instead of face-to-face with retailers. That's all good news for pharmacy benefits management companies like Caremark (NYSE:CMX).

Fourth-quarter sales were up 4% year over year. Not so hot, right? Well, operating income was up 17%, and adjusted pro forma earnings per share rose 22%. Operating leverage is the name of the game here -- taking more and more cost out of the equation while using the benefits of size and scale to become increasingly profitable.

Mail-order prescription fulfillment is more profitable for Caremark, and that side of the business continues to grow. Mail-based revenue was up 30% this quarter on a 20% increase in claims, while retail revenue fell 6% on a 21% drop in claims. Once again, though, EBITDA per average claim grew nicely, jumping 31% to $2.86.

Perhaps it should go without saying, but any lucrative enterprise will attract plenty of competition, and this one certainly qualifies. Customer volume is important in achieving pricing leverage, so it's key for Caremark not to lose much ground to the likes of Express Scripts (NASDAQ:ESRX) and MedcoHealth Systems (NYSE:MHS). And don't forget that health insurers like Aetna (NYSE:AET) and pharmacies like Walgreen (NYSE:WAG) and CVS (NYSE:CVS) have their own designs on the market as well.

Although a discounted cash flow analysis doesn't suggest much wiggle room in the price, this is a company worthy of long-term consideration. It has a history of high customer retention and deep experience in specialty pharmaceuticals management. Add into that the ongoing leverage potential of general cost reductions, and shifting more patients to mail-order fulfillment, and you can make a case that Caremark will continue to hit the mark in the years to come.

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Fool contributor Stephen Simpson has no financial interest in any stocks mentioned (that means he's neither long nor short the shares).