Lipitor is a brand name for the generic drug atorvastatin, which is a type of medication known as a statin. Statins are used to lower cholesterol levels in the blood, which can help prevent heart attacks and strokes. According to UpToDate [3], statins are generally well-tolerated, but they can cause liver damage in rare cases. Therefore, liver function tests are recommended before starting statin therapy and periodically thereafter to monitor for any potential liver damage.

The frequency of liver function monitoring for patients taking Lipitor may depend on various factors such as age, underlying medical conditions, and other medications the patient may be taking. According to a study published in the Journal of Clinical and Translational Hepatology [2], liver function tests should be performed at baseline and then at 12 weeks after starting statin therapy. If the tests are normal, then subsequent monitoring can be done every six months to a year. However, if the patient has pre-existing liver disease or is taking other medications that can affect liver function, more frequent monitoring may be necessary.

According to Drug Patent Watch [1], the prescribing information for Lipitor recommends liver function tests before starting therapy and then periodically thereafter. However, it does not specify a specific frequency for monitoring liver function.

In summary, patients taking Lipitor should have liver function tests performed before starting therapy and periodically thereafter to monitor for potential liver damage. The frequency of monitoring may depend on various factors and should be determined by a healthcare provider.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/LIPITOR
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5325661/
[3] https://www.uptodate.com/contents/statins-actions-side-effects-and-administration