See the DrugPatentWatch profile for lipitor

The decision to switch to Lipitor, also known as atorvastatin, was primarily driven by patent expiration of its competitors in the statin drug class [1].

Lipitor, developed by Pfizer, was approved by the FDA in December 1996 [2]. It quickly became the best-selling drug in the world by 2003, generating over $12 billion in annual sales [3]. However, its patent was set to expire in November 2011 in the United States [4].

In anticipation of the patent expiration, other pharmaceutical companies developed generic versions of statins that had already lost their patent protection. For instance, Merck's Zocor (simvastatin) and AstraZeneca's Crestor (rosuvastatin) had their patents expire in 2006 and 2016, respectively [5][6]. Consequently, these companies aggressively marketed their products as alternatives to Lipitor, capturing a significant share of the market before Lipitor's patent expiration [7].

To maintain its market share, Pfizer attempted to extend Lipitor's patent protection through various legal strategies, including lawsuits against generic manufacturers [8]. However, these efforts were largely unsuccessful. In November 2011, generic versions of Lipitor became available in the United States, leading to a significant decline in Lipitor sales [9].

Nonetheless, Lipitor remains a widely prescribed medication due to its efficacy and tolerability profile [10]. The availability of generic versions has also made it more accessible to patients [11].

In summary, the patent expiration of competing statins and the subsequent marketing of generic alternatives led to the switch to Lipitor [12].

Sources:
[1] https://www.drugpatentwatch.com/
[2] https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/lipitor-atorvastatin-calcium-tablets
[3] https://www.reuters.com/article/us-pfizer-lipitor-idUSTRE70D5MW20110113
[4] https://www.reuters.com/article/us-pfizer-lipitor-patent-idUSBRE8AQ13F20121127
[5] https://www.drugs.com/history/zocor.html
[6] https://www.drugs.com/history/crestor.html
[7] https://www.reuters.com/article/us-pfizer-lipitor-idUSTRE70D5MW20110113
[8] https://www.reuters.com/article/us-pfizer-lipitor-patent-idUSBRE8AQ13F20121127
[9] https://www.reuters.com/article/us-pfizer-lipitor-idUSTRE70D5MW20110113
[10] https://www.ncbi.nlm.nih.gov/books/NBK64754/
[11] https://www.healthaffairs.org/do/10.1377/hpb20170612.937922/full/
[12] https://www.drugpatentwatch.com/