Bulging fontanels have been associated with the use of tetracyclines in infants. While this is not problem in those with normal renal function, in patients with mika on sumycin significantly impaired function, higher serum levels of tetracycline may lead to azotemia, hyperphosphatemia, and acidosis. Tetracycline therapy of acne should augment the other standard measures known to be of value. Under no circumstances should outdated tetracyclines be administered, as the degradation of tetracyclines are highly nephrotoxic and have, on occasion, produced Fanconi-like syndrome. Women of child-bearing age should use effective birth control while taking this medication. Also there is chance that bacteria will develop resistance and will not be treatable by Sumycin or other antibacterial drugs in the future. Tell your doctor immediately if you develop: persistent diarrhea, abdominal or stomach pain cramping, blood mucus in your stool.