Lipitor is a commonly prescribed medication for managing high cholesterol levels. It is important to monitor the levels of Lipitor in the body to ensure that it is effective and safe for the patient. According to the sources provided, the frequency of monitoring Lipitor levels may vary depending on the patient's condition and other factors.

The first source, Drug Patent Watch [1], does not provide information on how often to monitor Lipitor levels. However, it provides details on the drug's patent status, generic availability, and other related information.

The second source, Medsafe [2], provides information on the potential side effects of statins, including Lipitor, and the need for monitoring patients for muscle-related symptoms. It suggests that patients should be advised to report any unexplained muscle pain, tenderness, or weakness, and that healthcare professionals should consider measuring creatine kinase (CK) levels if such symptoms occur. However, it does not provide specific guidance on how often to monitor Lipitor levels.

The third source, NCBI [3], discusses the importance of monitoring Lipitor levels in patients with liver or kidney disease, as these conditions can affect the drug's metabolism and elimination from the body. It suggests that healthcare professionals should monitor liver function tests and renal function tests regularly in such patients. However, it does not provide specific guidance on how often to monitor Lipitor levels in general.

In summary, the sources provided do not offer specific guidance on how often to monitor Lipitor levels. However, they emphasize the importance of monitoring patients for potential side effects and for liver and kidney function in certain cases. Healthcare professionals should consider the patient's individual circumstances and medical history when determining the appropriate frequency of monitoring Lipitor levels.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/LIPITOR
[2] https://medsafe.govt.nz/profs/puarticles/statinmyop.htm
[3] https://www.ncbi.nlm.nih.gov/books/NBK430779/