What Causes High Potassium Levels After Taking Losartan For High BP?

Question : My wife has been taking Losartan (50mg) for 7 days to get her BP down. It was at an average of 146/73 with an 81 pulse (with a high of 164/75 with an 84 pulse) after 7 days of Losartan her average is now 142/71 with a pulse of 84 (with a high of 155/73 with a pulse of 73). She was advised to take a potassium blood test within a week and it came back today with a 5.4 potassium reading (one month ago it was a 4.5). Her cardiologist is not in this week and the PA through the nurse told us to continue to take the Losartan but eliminate her multi- vitamin. We told the nurse that my wife's GNC Woman's Ultra XXXXXXX 50 Plus multi vitamin does not have potassium listed on the ingredients label but the nurse insisted that all multi vitamins have potassium. My concern is that we are doing the wrong thing. The multi has no potassium and the only variable with the higher potassium reading is the Losartan. The doctor should be back in on Monday can she stop taking the Losartan or can we go to 25mg.

Would reducing the Losartan to 25 mg until the next blood test be harmful? Would stopping the Losartan completely until the next blood test be harmful?