Hi & Welcome. Clindamycin can worsen the condition hence it should not be taken while suffering from crohn s disease. Treatment with antibiotics like Clindamycin alters the normal (useful) flora of the colon leading to overgrowth of pathogenic (harmful) flora Clostridium difficile which can cause severe diarrhea and inflammation of the colon. This can worsen the manifestations of Crohn s disease resulting in severe bloody diarrhea, abdominal cramps, fever and shock. Because Clindamycin therapy has been associated with severe colitis which may end fatally, it should not be used for the treatment of infections such as following the tooth extraction while suffering from Crohn s disease. So, since your son has already started frequent loose motions, Clindamycin should be discontinued immediately. Appropriate fluid and electrolyte management for dehydration and specific antibiotic like Vancomycin or Metronidazole may be required for the treatment of Clostridium difficile associated diarrhea. Hope the advice given above would be beneficial to him. Wishing your beloved son a quick and smooth recovery. A feed back is appreciated.