Concentration of doxycycline in bowel tissue and postoperative infections.

An investigation on the relation between the effect of doxycycline as prophylactic antibiotic in colonic surgery and levels of doxycycline in serum and bowel tissue with reference to MIC-values of bacterial strains isolated at surgery or after postoperative septic complications is presented. 200 mg doxycycline orally 4-6 hours preoperatively resulted in a serum concentration of 4.0 +/- 0.3 mug/ml at the onset of operation. Tissue samples removed at surgery were assayed for doxycycline. High levels were observed in bowel tissue, ileum 7.5 +/- 1.2 mug/ml and colon 3.9 +/- 0.3 mug/ml. The effects of dosage, time of administration and bowel pathology on tissue levels are discussed. Aerobic and anaerobic bacterial strains were tested for in vitro susceptibility to doxycycline using a standardized disc-diffusion method according to Eriksson and Sherris. 75% of the strains belonged to sensitivity groups 1 and 2 (sensitive-fairly sensitive). That is, MIC-values in 75% of the strains were below the average serum and intestinal tissue concentration during the operation. The implications of these results are that the dosage and time of administration of the drug must be adjusted so that serum and tissue levels are adequate during surgery.