After Lipitor, a popular cholesterol-lowering drug, lost its patent protection in 2011, several factors affected its revenue.

Firstly, the loss of exclusivity allowed generic versions of the drug to enter the market [1]. This increased competition led to a significant decline in Lipitor's market share. According to DrugPatentWatch.com, Lipitor's revenue dropped from $10.7 billion in 2011 to $2.1 billion in 2014 [2].

Secondly, the introduction of alternative treatments also impacted Lipitor's revenue. Other cholesterol-lowering drugs, such as Crestor and Zetia, gained popularity as they offered different mechanisms of action or administration methods [3].

Additionally, changes in healthcare policies and guidelines affected Lipitor's sales. For instance, the American College of Cardiology and the American Heart Association released new cholesterol management guidelines in 2013, which recommended statins as a class, rather than specific drugs like Lipitor [4].

Lastly, direct-to-consumer advertising (DTCA) played a role in Lipitor's revenue post-patent expiration. Pfizer, the manufacturer of Lipitor, spent $258 million on DTCA in 2012, but this figure dropped to $124 million in 2013 [5]. The decrease in advertising spend could have contributed to the decline in Lipitor's revenue.

In conclusion, the loss of patent exclusivity, increased competition, alternative treatments, changes in healthcare policies, and reduced advertising spend were key factors that affected Lipitor's revenue after patent expiration.

Sources:
[1] "Lipitor (Atorvastatin)". Drugs.com. https://www.drugs.com/lipitor.html
[2] "Lipitor (Atorvastatin)". DrugPatentWatch.com. https://www.drugpatentwatch.com/drugs/lipitor
[3] "Statins". Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/high-blood-cholesterol/in-depth/statins/art-20045936
[4] "2013 ACC/AHA Guideline on the Treatment of Blood Cholesterol to Reduce Atherosclerotic Cardiovascular Risk in Adults". Journal of the American College of Cardiology. https://www.jacc.org/doi/10.1016/j.jacc.2013.11.002
[5] "Direct-to-Consumer Advertising". Food and Drug Administration. https://www.fda.gov/drugs/information-consumers-and-patients-consumer-updates/direct-consumer-advertising