Source: Pfizer via Facebook.

Pfizer (NYSE:PFE) may be one of the planet's largest drugmakers, but it's been navigating a series of sales-crunching patent expirations that has investors wondering if the company's dividend payout will remain intact. Let's take a closer look and see whether or not investors should be concerned.

Obstacles to growth
In 2011, Pfizer lost patent protection on its top-selling cholesterol-busting drug Lipitor. Lipitor was a massively successful commercial drug that generated more than $13 billion in sales at its peak. Since losing patent exclusivity, however, sales of Lipitor have plummeted to just $2 billion in 2013. Sales have continued to sag this year, too. In the third quarter, Lipitor revenue slumped an additional 8% from last year, to $490 million.

Lipitor's sales slide has created quite a hurdle for Pfizer; but it's not the only drug that is seeing sales decline. Pfizer's top-selling Viagra lost patent protection in Europe last year and, as a result, its sales fell 7%, to $427 million last quarter. In addition to Lipitor and Viagra, Pfizer's product lineup includes 10 other therapies that saw their sales drop 10% or more year over year in the quarter.

The patent calendar doesn't appear to be getting much friendlier for Pfizer, either. Beginning in December, the company's anti-inflammatory drug Celebrex will start seeing some of its roughly $3 billion in annual sales eaten away by generic versions made by Teva Pharmaceuticals (NYSE:TEVA) and Actavis (NYSE:AGN)

Source: Pfizer via Facebook

Reasons for dividend hope
Although patent expiration is weighing on growth, the outlook for Pfizer's product lineup isn't all bleak. The company has a slate of promising therapies that are growing quickly and helping offset the headwind.

Sales of the company's Lyrica, which treats a variety of conditions including shingles, have jumped 13% year over year, to $3.7 billion through the first nine months of 2014. Since Lyrica won't lose patent protection until 2018, it should continue to boost Pfizer's top line. 

Pfizer is enjoying rapid growth for Xalrori and Inlyta, too. Xalkori, a drug used to treat certain lung cancers, saw its sales jump 60%, to $308 million last quarter, and sales of Inlyta, a kidney cancer drug, have grown 34%, to $291 million in Q3.

Fast growth for these cancer drugs offers some hope to dividend investors, but investors should also be encouraged by Pfizer's balance sheet. The company has $33 billion in cash and equivalents, and another $18 billion in long-term investments on the books. That's good enough to help give Pfizer a healthy current ratio -- a measure the company's ability to cover liabilities if debtors come knocking -- of 2.86.

In addition to a seemingly rock-solid balance sheet, dividend investors can also sleep better knowing that Pfizer's cash dividend payout ratio isn't sky-high, either. The cash dividend payout ratio measures how much of the company's cash is used to pay its dividends after paying for capex and preferred dividends.  At 42%, the measure suggests that there's no imminent threat that would cause Pfizer to cut its dividend payout.

PFE Cash Dividend Payout Ratio (TTM) Chart

PFE Cash Dividend Payout Ratio (TTM) data by YCharts.

Fool-worthy thoughts
There's no question that Pfizer has some operational struggles that it's wrestling to overcome. But with fast-growing cancer drugs like Xalkori, a strong balance sheet, and a reasonable cash dividend payout ratio, the company's dividend payment appears to be safe. That's likely good news for investors given that Pfizer's 3.4% dividend yield is quite competitive relative to other big drugmakers.