Hi and thank you so much for this query. I am so sorry to hear about this cellulitis. Keflex cannot cause this sudden and alarming increase in blood pressure. I will suggest that you get your father to the emergency room because these numbers are very high and need immediate attention to avoid related complications like stroke, heart, kidney damages, etc. Cellulitis in diabetics should be approached with full force because of the fear of severe complications. If the improvement is not remarkable withing 48hours, please talk to his treating doctor. I hope this helps. I wish you well. Dr. Ivo, D.