Source: Pixabay.

The stock market's aging rally is under threat from the economic calamities taking place in Greece and, to a lesser extent, Puerto Rico. Then again, the market might simply be due for a healthy correction, particularly after most major indices have posted unprecedented growth over the last five years or so:

SPY Chart

Although the time seems ripe for a downside correction, you can never really know what the market is going to do, or how long it's going to do it for. That said, I think now is probably a good time to get a tad more defensive with your portfolio, and one way to do so is to grab some top dividend payers in the healthcare sector.

These stocks tend to be resistant to stock market plunges because their underlying businesses are generally independent of the economic environment at large, and their dividends attract investors seeking steady income, not growth. Armed with this insight, let's look at why Amgen (AMGN -0.19%) and AstraZeneca (AZN 0.49%) might be worth picking up amid these global economic headwinds.   

Amgen is a top biotech that offers sustainable growth, rising cash flow, and a safe dividend
Like most of its biotech peers, Amgen's stock has soared over the last few years. But a deep look under the hood shows this near-parabolic move upward is backed by fundamentals, not hype. Specifically, Amgen's rise has been driven by a host of growth products such as Enbrel, Prolia, and Xgeva, allowing the company to continually raise its dividend -- giving it a respectable yield of roughly 2% at current levels.

Most importantly, Amgen's double-digit earnings and revenue growth rate is expected to continue for the foreseeable future due to the company's robust clinical pipeline, headlined by blockbusters-in-waiting Repatha for high cholesterol and Kyprolis for relapsed multiple myeloma. Amgen also sports one of the deepest biosimilar pipelines, which is expected to generate upward of $3 billion in annual sales moving forward. This would offset any losses from Amgen's own line of biologics going off patent protection, such as the white blood cell growth stimulator Neupogen.  

AstraZeneca could be a sleeping giant in the healthcare sector
AstraZeneca has been pummeled by the loss of Nexium and other former top-selling drugs to the patent cliff. However, the British pharma giant has been repositioning itself to become a global leader in the high-growth markets of diabetes care and cancer immunotherapy. The drugmaker's diabetes franchise, composed of products such as the Bydureon pen device and the SGLT-2 inhibitor Forxiga, for instance, posted whopping 47% year-over-year sales growth, to $488 million, in the first quarter of this year.

Source: Flickr via user Rennet Stowe

The main takeaway is that Astra's growth products are helping the drugmaker come in for a softer-than-expected landing after it lost a number of key products. All told, management predicts its revenue to decline by only mid-single-digits this year, meaning the company's monstrous 4.35% dividend yield should be safe.

Looking ahead, Astra believes it is on track to return to growth by 2017, mainly on the back of its emerging cancer immunotherapy pipeline. In its latest clinical update, Astra said it is conducting 16 mid- and late-stage trials within the cancer immunotherapy space. The hope is this bevy of clinical activity can lead to a handful of regulatory filings within the next 12 months.

The most exciting part, however, is Astra's host of external collaborations with top cancer specialists such as Celgene Corp. that could lead to truly game-changing combination therapies for hard-to-treat blood-based cancers. Astra's management has even mentioned that it is interested in acquiring a leading CAR-T therapy company such as Juno Therapeutics or Kite Pharma, which would give the drugmaker another major competitive advantage in the burgeoning immunotherapy market. 

Are these two healthcare stocks worth buying right now?
Amgen and Astra might not garner headlines like some of their peers, but these are two solid stocks that merit a deep look by investors searching for sustainable growth and income. I particularly like these stocks as defensive plays against the unfolding macroeconomic issues because their current valuations -- based on their trailing and forward price-to-earnings ratios -- are actually well below the sector's averages on these closely watched metrics. This means they probably won't fall as hard in a marketwide correction as other healthcare stocks that are trading in the upper stratosphere right now.