Is combinig Lipitor and Zocor safe and effective?

I have been on Lipitor 10 mg for over 15 yrs, starting in the clinical trials before commercialization. It was very effective in lowering my cholesterol and I have had no side effects. Recently my cholesterol elevated without apparent cause. My doctor switched me to Zocor 40mg vs 20mg Lipitor for cost savings. This was not effective in reducing my cholesterol. She now wants to increase it to 80 mg. I want to try a cobination of 40 mg Zocor plus 20 mg Lipitor, which is equivalent to 80 mg of Zocor. My question is, is the combination safe and what other concerns considerations are there?

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