The next two to four years are an important time frame for many pharmaceutical companies. It is when many of the top-selling drugs go off patent. Here is a list of the large pharma companies with some of their top-selling drugs that are set to "expire" and open up to competition.

AstraZeneca (AZN) has the cholesterol drug Crestor, which is set to go off patent in the year 2012. This was recently ranked the 42nd best selling drug. Its asthma drug, Symbicort, expires the same year. Its Seroquel, an antipsychotic used to treat schizophrenia and the 16th best selling drug, expires 2011. The stock has a price-to-earnings (P/E) ratio of 11, a P/E-to-growth (PEG) ratio of 2.77 and pays a yield of 4.6%.

Eli Lilly (LLY) has the eighth best selling drug, Zyprexa, which is used to treat schizophrenia and has a patent expiration of 2011. It also has Actos for Type 2 diabetes, which goes off patent the same year. Lilly has a P/E of 19, a PEG of 1.8 and a yield of 3.6%.

Forest Laboratories (FRX) has the drug Lexapro, also known as Cipralex, which expires in 2012. The drug is an antidepressant used to treat depression and anxiety disorders. The stock has a P/E of 23 and a PEG of 1.1.

GlaxoSmithKline (GSK) has the asthma drug Advair, also known as Seretide, which expires in 2010, and diabetes drug Avandia, which expires in 2012. The stock has a P/E of 12, a PEG of 4.21 and a yield of 5.6%.

Johnson & Johnson's (JNJ) antibiotic drug, Levaquin, goes off patent in 2010. The stock has a P/E of 18, a PEG of 1.99 and a yield of 2.5%.

Merck & Co. (MRK) has asthma drug Singulair, which expires in 2012, and Cozaar for hypertension expiring 2010. The stock has a P/E of 27, a PEG of 1.21 and a yield of 4%.

Novartis AG (NVS) has the Zometa cancer drug and the Diovan hypertension drug, both expiring 2012. The stock has a P/E of 10, a PEG of 1.22 and a yield of 2.9%.

Pfizer (PFE) has Lipitor for cholesterol, estimated to expire 2010, Aricept for Alzheimer's, expiring 2010, and Xalatan for glaucoma, going off patent 2011. The stock has a P/E of 18, a PEG of 2.03 and a 6% yield.

Both Sanofi-Aventis (SNY) and Bristol-Myers Squibb (BMY) have Aprovel for high blood pressure expiring 2011, and the anticoagulant Plavix, expiring the same year.

By Stockerblog.com.

Author owns PFE.