Tenoxicam i.v. for major gynaecological surgery--effects on renal function

Thirty women presenting for major gynaecological oncology surgery under a standardized, combined epidural/general anaesthetic technique received either placebo or tenoxicam 20 mg intravenously, in a randomized double-blinded manner prior to surgery. Plasma and urinary electrolytes, creatinine, prostaglandins PgE2 and PgF1 alpha, and thromboxane (TxB2) were collected 12 hours preoperatively and then for four days postoperatively. There were no significant differences in any of the measured parameters between the groups, at any of the measurement times. Mean (SD) creatinine clearance at baseline, 24 h and 48 h was 100.4 (29.7) and 86.9 (27.5), 128.1 (45.9) and 115.0 (40.3), 137.5 (50.7) and 121.6 (38.6) in the placebo and tenoxicam groups respectively (P = 0.28). Both groups required similar amounts of intraoperative ephedrine and intravenous fluids to maintain blood pressure. The minimal changes in plasma and renal parameters reflect predictable responses to major surgery and rehydration rather than any response to cyclooxygenase inhibition. This may underscore the importance of maintenance of blood pressure during the course of surgery and postoperative care, and perhaps the usefulness of a fluid loading regimen to preserve renal function during surgery. The predicted attenuation of renal prostaglandin-mediated protective mechanisms and enhancement of the catecholamine-mediated renal vasoconstriction by the use of a single 20 mg dose of tenoxicam in this study were not seen. Modulation of renal concentrating mechanisms or excretion of sodium and potassium by tenoxicam was not apparent and a large increase in study size would be required to detect a significant difference in these parameters as a consequence of the drug, over and above any changes in response to surgery and epidural anaesthesia.