Predictors of trough concentrations of oral ciprofloxacin

Patients enrolled in a fixed-dose clinical trial of oral ciprofloxacin had trough concentrations measured to document absorption and monitor compliance. The objective was to determine whether any demographic characteristics might be important predictors of the concentrations. Stepwise multivariate linear regression revealed no correlation between ciprofloxacin trough concentrations and serum creatinine, estimated creatinine clearance (Clcr), weight, height, body surface area, or gender. However, age exhibited a direct linear relationship with trough concentrations (Y in microgram/ml), Y = 0.020.age--0.541 (p < 0.003). We conclude that for patients with Clcr 30 ml/minute or above, age is a more important predictor of ciprofloxacin trough concentration than renal function. Dosage adjustment should not be arbitrary but should be guided by minimum inhibitory concentration, clinical response, and side effects.