Pfizer (NYSE: PFE) careened off the patent cliff in more spectacular fashion than perhaps any other pharmaceutical company. The company lost U.S. patent protection for blockbuster cholesterol drug Lipitor and heart burn drug Protonix in 2011. Other big-selling drugs go off-patent within the next few years.

Are there replacements that could possibly make up for lost revenue from these superstar drugs? Let's take a peek at Pfizer's pipeline to evaluate some of the top contenders.

In the pipeline
Pfizer currently has 87 drugs in its pipeline. Most of these are in either early or mid-stage trials, but 11 drugs are in registration.

Source: Pfizer.com.

The company isn't putting all of its eggs in one basket. The drugs in the pipeline represent a relatively evenly distributed mix of therapeutic areas.

Source: Pfizer.com

In terms of sheer numbers, Pfizer appears to be ahead of other large rivals facing significant loss of revenue because of patent expiration. Eli Lilly (NYSE: LLY) isn't far behind, with 62 drugs in the phase 1 through phase 3 stages of its pipeline, plus one drug in regulatory review.

Bristol-Myers Squibb (NYSE: BMY) has 46 drugs in exploratory development and seven drugs in registration. Merck (NYSE: MRK) claims 35 drugs in phase 2 or phase 3 trials, with two under review. Johnson & Johnson's (NYSE: JNJ) pipeline includes 18 drugs that are either in phase 3 clinical trials or up for FDA approval.

Quality trumps quantity, though. One or two blockbusters can be better than several lower-revenue drugs.

Most likely to succeed
So, which -- if any -- of the drugs in Pfizer's pipeline could be the next big winners? Three stand out in my view.

Bosutinib recently received FDA approval for treating chronic myeloid leukemia. CML accounts for 15% of all leukemia diagnoses across the world. Other treatments are available for CML, but bosutinib offers another potential option for patients -- especially those who don't respond well to other drugs.

Another medication in Pfizer's pipeline, tofacitinib, could score on multiple counts. The drug is in registration for treating rheumatoid arthritis. Phase 3 trials are moving along for tofacitinib in treating ulcerative colitis and psoriasis. Some analysts project a potential $2 billion annual market for the drug.

Pfizer also has high hopes for blood thinner Eliquis. At least one analyst pegs the potential market for Eliquis at $2.5 billion annually. However, the company and partner Bristol-Myers Squibb hit a snag recently when the FDA asked for clarification from some clinical studies. Pfizer seems to see this as only a temporary setback.

Big shoes to fill
Lipitor alone makes for some big shoes to fill. Adding the other drugs for which Pfizer has lost or is losing patent protection only increases the size of those shoes.

Despite having some drugs in the pipeline with strong potential, Pfizer probably won't fully regain its sales levels from its peak Lipitor years any time soon. As the old saying goes, though, "Rome wasn't built in a day." Climbing back from the bottom of a patent cliff takes time, too.

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