blood thinners not working

[amydee]

My father recently suffered from a mild stroke...TIA I beleive. The doctors have put him on a herparin IV drip, coumadin pill, zocor, altace,glucopase, and pepcid AC. When he entered the hospital his INR level was 1 and now after 2 weeks it is 1.61 They need it to get to 2.4 before  he can be released. He was given 5mg of coumadin and his levels did not increase. He was give 7.5 mg and the level dropped from 1.6 to 1.58 and then 1.4. He is now on 10mg and his level is back at 1.6 but is not getting any better.  He was also diagnosed with diabetes and is eating a retrictive diet. We know that vitamin K should be avoided but he does enjoy salads with romaine lettuce that we have been bring to the hospital. Why are his levels not rising with the coumadin and the heparin? Are they any possible drug interactions with what he is taking?

Thank you