According to the sources provided, Lipitor (atorvastatin) can be taken with or without food, and it does not need to be taken with skim milk specifically. The drug labeling information provided by Pfizer [2] states that Lipitor can be taken with or without food, and the MedlinePlus website [3] confirms that Lipitor can be taken with or without food. There is no mention of skim milk specifically being required or recommended for the medication to be effective. The Drug Patent Watch website [1] provides information about the expiration of Lipitor's patent, but does not provide any information about how the medication should be taken. It is important to follow the instructions of a healthcare provider or pharmacist when taking Lipitor or any medication.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/LIPITOR
[2] https://labeling.pfizer.com/showlabeling.aspx?id=587§ion=PPI
[3] https://medlineplus.gov/druginfo/meds/a600045.html