That's considered to be the maximal dose so I'd consider talking to my doctor about other treatment options.  I'd also point out that if you are on Lipitor for cholesterol control then that signals to me that artery clogging plaque may be interferring with your sexual function and specifically causing ED.  Along with the Lipitor I would be exercising (get an "exercise prescription for aerobic and a weight training regimen from your doctor or hire a personal trainer for some education) and consider increasing fruits and vegetables in your diet, switching over to some lean proteins like egg whites, skinless white meats, fish and beans (get the red meat out of your diet) and go low fat or fat free when choosing dairy products.  Make sure you're eating less saturated fat and using small amounts of healthy fats from nuts, olive oil, nut oils, avocadoes.  Your diet and exercise changes can help to clear plaque from the arteries that supply blood to your heart AND your genitalia.