Lipitor (atorvastatin) and Warfarin are commonly prescribed drugs used to manage high cholesterol and blood clotting disorders, respectively. When used together, they can interact and increase the risk of bleeding. Therefore, it is essential to monitor the patient's INR (International Normalized Ratio) regularly. The INR measures the blood's ability to clot, and the desired range depends on the condition being treated.

According to the National Health Service (NHS) [2], when Lipitor and Warfarin are prescribed together, the patient's INR should be monitored regularly, typically every two to four weeks, until it stabilizes within the desired range. After that, the frequency of monitoring can be reduced to every four to six weeks, or as advised by the healthcare provider. However, the frequency of monitoring may vary depending on the patient's age, medical history, and other medications they are taking.

The drug patent watch [1] website provides information on the dosage and administration of Lipitor. It states that the recommended starting dose for Lipitor is 10-20 mg once daily, and the maximum dose is 80 mg/day. However, the dosage may vary depending on the patient's medical condition and response to treatment.

A recent study [3] published in the Journal of Pharmacy Practice and Research recommends that healthcare providers should consider regular INR monitoring and patient education when prescribing Lipitor and Warfarin together. The study found that many patients were not aware of the potential drug interaction, and their INR was not monitored as frequently as recommended. Therefore, it is crucial to educate patients about the risks and benefits of these medications and monitor their INR regularly to prevent adverse effects.

In conclusion, when Lipitor and Warfarin are prescribed together, the patient's INR should be monitored regularly, typically every two to four weeks, until it stabilizes within the desired range. After that, the frequency of monitoring can be reduced to every four to six weeks, or as advised by the healthcare provider. The dosage of Lipitor may vary depending on the patient's medical condition and response to treatment. Healthcare providers should consider regular INR monitoring and patient education to prevent adverse effects.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/LIPITOR
[2] https://www.nhs.uk/conditions/statins/considerations/
[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8861410/