Lipitor is a statin drug used to lower cholesterol levels in the blood, which can reduce the risk of heart disease and stroke. According to the British Heart Foundation [2], when starting on Lipitor, your doctor will usually monitor your liver function and cholesterol levels with a blood test after four to six weeks. Once your levels are stable, the tests may be repeated every six to 12 months. However, the frequency of monitoring may vary depending on individual factors, such as age, overall health, and other medications being taken.

Drug Patent Watch [1] provides information about the patent and exclusivity status of Lipitor but does not offer guidance on how often to check Lipitor dosage.

The National Center for Biotechnology Information [3] provides a comprehensive guide to Lipitor, including its uses, dosage, side effects, and monitoring. The guide recommends monitoring liver function tests before starting treatment and periodically thereafter. However, it does not provide specific guidance on how often to check Lipitor dosage.

In summary, the British Heart Foundation recommends monitoring liver function and cholesterol levels with a blood test after starting Lipitor and repeating the tests every six to 12 months once levels are stable. However, the frequency of monitoring may vary depending on individual factors, and patients should consult their doctor for specific guidance.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/LIPITOR
[2] https://www.bhf.org.uk/informationsupport/heart-matters-magazine/medical/drug-cabinet/statins
[3] https://www.ncbi.nlm.nih.gov/books/NBK430779/