Hello
Acyclovir is known to cause abdominal pains. Talk to your doctor about modification of the dose or for addition of certain anti-hyperacidity medicines like pantoprazole. However, it is unlikely to cause the bloody stools. Rather it is more likely that you have got a bacterial infection along. The infection needs to be treated with antibiotics. Please get a stool routine microscopy test done and visit your doctor with the report. Based on that he will be able to administer proper antibiotics which are essential in such a case. Take Oral rely Chat Doctor.