Some medications can affect urinalysis by making your urine appear darker, notes the NLM. Chloroquine, phenothiazine, ibuprofen, deferoxamine, metronidazole, phenytoin, rifampin, imipenem/cilastatin, phenolphthalein, and nitrofurantoin can change the color of your urine. You need to tell your doctor about your medications and let them know if you are taking medications that affect urinalysis.