Hi, My Husband Has Lung Cancer That Has Spread To

Hi, my husband has lung cancer that has spread to his brain. He has developed a red rash on his chest. The Dr has prescribed SMZ-TMP DS 800-160 mg tabs. He is supposed to take 3 pills per week. I gave him 2 pills yesterday and 3 pills today by mistake. Should I be worried?? There are no apparent side affects.