The expiration of Lipitor's patent had a significant impact on its revenue. Lipitor, a cholesterol-lowering drug manufactured by Pfizer, was the best-selling drug in the world before its patent expired [1].

Prior to the patent expiration, Lipitor generated approximately $13 billion in annual sales for Pfizer [1]. However, after the patent expired in November 2011, generic versions of the drug, such as atorvastatin, entered the market, leading to a decline in Lipitor's revenue.

According to a report by DrugPatentWatch.com, the introduction of generic Lipitor led to a 90% decline in Lipitor's sales within a year of the patent expiration [2]. The report states that the loss of exclusivity for Lipitor resulted in a significant decrease in revenue for Pfizer, as the company faced intense competition from generic manufacturers [2].

The decline in Lipitor's revenue had a significant impact on Pfizer's overall financial performance. In 2012, the year following the patent expiration, Pfizer reported a 17% decline in revenue, which the company attributed to the loss of exclusivity for Lipitor [3].

In summary, the expiration of Lipitor's patent had a substantial impact on its revenue, leading to a significant decline in sales and a negative impact on Pfizer's overall financial performance.

Sources:

1. "Lipitor (atorvastatin) - Drug Uses, Side Effects, Interactions, Pictures, Warnings & Dosing." RxList, <https://www.rxlist.com/lipitor-drug.htm>.
2. "Lipitor (Atorvastatin) Patent Expiration, Generic Entry & Sales." DrugPatentWatch, 13 Nov. 2019, <https://www.drugpatentwatch.com/lipitor-patent>.
3. "Pfizer Reports Fourth-Quarter and Full-Year 2012 Financial Results." Pfizer, 29 Jan. 2013, <https://www.pfizer.com/news/press-release/press-release-detail/pfizer_reports_fourth-quarter_and_full-year_2012_financial_results>.