According to pharmaceutical market research giant IMS Health, global pharma sales grew 5.1% to $956 billion between 2010 and 2011. This represented an all-time high and was nearly double the level of $503 billion back in 2003. Growth has slowed from closer to 9% annually roughly a decade ago, but continues to advance at a very healthy clip. Below is an overview of five of the best-selling individual drugs of all time.


Lipitor
By a wide margin, Pfizer's Lipitor qualifies as the best-selling drug of all time. The blockbuster drug, which is used to lower cholesterol levels, was first introduced to the market in 1997 and had a strong run of exclusivity until its patent expired in late 2011. Its rise in popularity was attributed to the fact it lowered cholesterol faster than competing statin drugs, according to certain studies. One source put the drug's total sales up through 2011 at around $125 billion cumulatively. This included peak revenue years above $10 billion annually during 2009 and 2010.

Sales have fallen dramatically now that the drug faces generic competition.


Plavix
Plavix is offered by the pharma giants Sanofi and Bristol-Myers Squibb and is used to help lower the risk of heart attack or stroke. Like Lipitor, Plavix now faces generic competition and saw the approval of seven companies to sell the identical generic version in pharmacies back in May. However, it had a long run of annual sales levels in the multi-billion-dollar range. Its 2011 rank was number two at $9.3 billion in sales, which put it just behind Lipitor. For the five-year period between 2007 and 2011, Plavix logged total sales of $43.2 billion to place it firmly among the top-selling drugs of all time.


Seretide
Seretide logged 2011 sales of $8.7 billion, which was its best year ever. The drug is sold by GlaxoSmithKline and is used to treat asthma. Seretide saw generic competition a couple of years ago in many of its global markets, but still holds protection in others, which is helping it hold onto many billions in annual sales.

The compound is also said to be difficult to copy, which helps keep Glaxo's original version selling well.


Crestor
Crestor is another cholesterol-lowering drug that competes with Lipitor and the wide range of current generic alternatives. The drug's owner is pharma giant AstraZeneca, and it appears the drug maintains patent protection in most of its large markets. In 2011, it was the fourth best-selling drug at $8 billion. This qualified as its best year ever, and the expiration of a couple of larger drugs above should allow Crestor to continue to build on its ranking as one of the best-selling drugs.


Humira
Humira is Abbott Laboratories' popular anti-arthritis drug. With Lipitor falling by the wayside, Humira is set to become the world's best-selling drug in 2012. Its 2011 sales came in at $7.3 billion, but sales are constantly on the rise. The drug is growing briskly and is the envy of rivals who have seen drugs fall by the wayside due to generic competition.


The Bottom Line
The patent expiration cliff of many blockbuster drugs makes it unlikely that many druge in the future will log sales above $10 billion annually.

However, $1 billion in annual sales is all that is needed to technically qualify a drug as a blockbuster drug. Many of the above prescription medications should continue to achieve these sales levels in the near future despite the fact that many are already seeing generic competition.