A patient with a serious fungal infection of the sinuses caused by Rhizopus arrhizus received the antifungal drug isavuconazole. However, blood tests showed the drug was building up to dangerously high levels in her body. Genetic testing revealed she had a mutation that made her body unable to break down the drug normally. The doctors had to give her much smaller and less frequent doses while carefully monitoring her drug levels to keep her safe.