DETERMINATION OF CIPROFLOXACIN LEVELS IN CHINCHILLA MIDDLE-EAR EFFUSION AND PLASMA BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH FLUORESCENCE DETECTION

An isocratic high-performance liquid chromatographic method has been d eveloped to determine ciprofloxacin levels in chinchilla plasma and mi ddle ear fluid. Ciprofloxacin and the internal standard, difloxacin, w ere separated on a Keystone ODS column (100 x 2.1 mm I.D., 5 mum Hyper sil) using a mobile phase of 30 mM phosphate buffer (pH 3), 20 mM trie thylamine, 20 mM sodium dodecyl sulphate-acetonitrile (60:40, v/v). Th e retention times were 3.0 min for ciprofloxacin and 5.2 min for diflo xacin. This fast, efficient protein precipitation procedure together w ith fluorescence detection allows a quantification limit of 25 ng/ml w ith a 50 mul sample size. The detection limit is 5 ng/ml with a signal -to-noise ratio of 5:1. Recoveries (mean +/- S.D., n = 5) at 100 ng/ml in plasma and middle ear fluid were 89.4 +/- 1.2% and 91.4 +/- 1.6%, respectively. The method was evaluated with biological samples taken f rom chinchillas with middle ear infections after administering ciprofl oxacin.