According to the provided sources, liver monitoring is important for patients taking Lipitor, a cholesterol-lowering statin drug. The recommended frequency of liver monitoring may vary depending on the patient's medical history and other factors.

The FDA has issued safety communication [3] regarding the use of statin drugs, including Lipitor, stating that liver function tests should be performed before starting treatment and as clinically indicated thereafter. The communication also states that routine monitoring of liver enzymes is no longer recommended for patients taking statins, including Lipitor, unless clinically indicated.

The prescribing information for Lipitor [1] recommends liver function tests before starting treatment and as clinically indicated thereafter. The frequency of liver function tests may vary depending on the patient's medical history, the dose of Lipitor, and other factors that may increase the risk of liver problems.

A review article [2] on the safety and efficacy of statins suggests that liver function tests should be performed before starting statin therapy and periodically thereafter, especially in patients with pre-existing liver disease or other risk factors for liver problems. The article suggests that the frequency of liver function tests may depend on the patient's risk profile and the dose of the statin.

In summary, liver monitoring is important for patients taking Lipitor, and the frequency of monitoring may vary depending on the patient's medical history and other factors. Patients should have liver function tests before starting treatment and as clinically indicated thereafter, with the frequency of testing determined by their healthcare provider.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/LIPITOR
[2] https://www.ncbi.nlm.nih.gov/books/NBK548236/
[3] https://www.fda.gov/drugs/drug-safety-and-availability/fda-drug-safety-communication-important-safety-label-changes-cholesterol-lowering-statin-drugs