Pharmacokinetics of pradofloxacin and doxycycline in serum, saliva, and tear fluid of cats after oral administration.

The pharmacokinetic properties of pradofloxacin and doxycycline were investigated in serum, saliva, and tear fluid of cats. In a crossover study design, six cats were treated orally with a single dose of pradofloxacin (Veraflox Oral Suspension 2.5%) and doxycycline (Ronaxan 100 mg) at 5 mg/kg body weight. Following administration, samples of serum, saliva, and tear fluid were taken in regular intervals over a period of 24 h and analysed by turbulent flow chromatography/tandem mass spectrometry. All values are given as mean +/- SD. Pradofloxacin reached a mean maximum serum concentration (C(max)) of 1.1 +/- 0.5 microg/mL after 1.8 +/- 1.3 h (t(max)). In saliva and tear fluid, mean C(max) was 6.3 +/- 7.0 and 13.4 +/- 20.9 microg/mL, respectively, and mean t(max) was 0.5 +/- 0 and 0.8 +/- 0.3 h, respectively. Doxycycline reached a mean C(max) in serum of 4.0 +/- 0.8 microg/mL after 4.3 +/- 3.2 h. Whilst only at two time-points doxycycline concentrations close to the limit of quantification were determined in tear fluid, no detectable levels were found in saliva. The high concentrations of pradofloxacin in saliva and tear fluid are promising to apply pradofloxacin for the treatment of conjunctivitis and upper respiratory tract infections in cats. As doxycycline is barely secreted into these fluids after oral application the mechanisms of its clinical efficacy remain unclear.