Effects of triclabendazole on secretion of danofloxacin and moxidectin into the milk of sheep: role of triclabendazole metabolites as inhibitors of the ruminant ABCG2 transporter.

ATP-binding cassette transporter G2/breast cancer resistance protein (ABCG2/BCRP) mediates drug-drug interactions that affect the secretion of drugs into milk. The aims of this study were: (1) to determine whether the major plasma metabolites of the flukicide triclabendazole (TCBZ), triclabendazole sulfoxide (TCBZSO) and triclabendazole sulfone (TCBZSO2), inhibit ovine and bovine ABCG2 and its Y581S variant in vitro, and (2) to examine whether coadministration of TCBZ with the ABCG2 substrates danofloxacin (a fluoroquinolone) and moxidectin (a milbemycin) affects the secretion of these drugs into the milk of sheep. TCBZSO and TCBZSO2 inhibited ruminant ABCG2 in vitro by reversing the reduced mitoxantrone accumulation and reducing basal to apical transport of nitrofurantoin in cells transduced with bovine variants (S581 and Y581) and the ovine variant of ABCG2. Coadministration of TCBZ with moxidectin or danofloxacin to sheep resulted in significantly reduced levels of moxidectin, but not danofloxacin, in the milk of TCBZ-treated sheep compared to sheep administered moxidectin or danofloxacin alone. The milk area under concentration time curve (AUC 0-48 h) was 2.99±1.41 µg h/mL in the group treated with TCBZ and moxidectin, and 7.75±3.58 µg h/mL in the group treated with moxidectin alone. The AUC (0-48 h) milk/plasma ratio was 37% lower in the group treated with TCBZ and moxidectin (7.34±1.51) than in the group treated with moxidectin alone (11.68±3.61). TCBZ metabolites appear to inhibit ruminant ABCG2 and affect the secretion of ABCG2 substrates into milk of sheep.

Simultaneous determination of albendazole metabolites, praziquantel and its metabolite in plasma by high-performance liquid chromatography-electrospray mass spectrometry.

The analysis of albendazole sulfoxide, albendazole sulfone, praziquantel and trans-4-hydroxypraziquantel in plasma was carried out by high-performance liquid chromatography-mass spectrometry ((LC-MS-MS). The plasma samples were prepared by liquid-liquid extraction using dichloromethane as extracting solvent. The partial HPLC resolution of drug and metabolites was obtained using a cyanopropyl column and a mobile phase consisting of methanol:water (3:7, v/v) plus 0.5% of acetic acid, at a flow rate of 1.0 mL/min. Multi reaction monitoring detection was performed by electrospray ionization in the positive ion mode, conferring additional selectivity to the method. Method validation showed relative standard deviation (precision) and relative errors (accuracy) lower than 15% for all analytes evaluated. The quantification limit was 5 ng/mL and the linear range was 5-2500 ng/mL for all analytes. The method was used for the determination of drug and metabolites in swine plasma samples and proved to be suitable for pharmacokinetic studies.

Voltammetric determination of praziquantel in tablets and biological fluids.

A simple method is described for the determination of praziquantel (CAS 55268-74-1) in its pure form, tablet formulations and biological fluids. The proposed method depends upon the polarographic activity of praziquantel at the dropping mercury electrode (DME) in Britton Robinson buffers, whereby a well-defined catholic wave is produced over the pH range 7-12. The wave was characterized as being irreversible diffusion-controlled with limited adsorption properties. The diffusion current constant (Id) was 0.56 +/- 0.004 (n = 11). The current-concentration relationship was found to be rectilinear over the range 8-48, 3.2-38.4 and 0.48-20 micrograms.ml-1 using direct current (DCt), differential pulse polarographic (DPP) and alternating current (ACt) odes, respectively, with minimum detection limit (S/N = 2) of 0.32 microgram.ml-1 (1.02 x 10(-6) mol/l and 0.02 microgram.ml-1 (6.4 x 10(-8) mol/l) for DPP and ACt modes respectively. The average percent recovery was favourably compared to a reference method with a satisfactory standard deviation. The proposed method was applied to spiked human urine and plasma. The percentage recoveries were 99.33 +/- 0.79 and 98.23 +/- 0.53, respectively.

Enantioselective analysis of praziquantel in plasma samples.

A direct enantioselective high-performance liquid chromatography method is described for the quantitative determination of praziquantel enantiomers in plasma samples. The method involves two-step extraction of plasma with toluene, evaporation of the solvent and chromatography on a Chiralcel OD-H column using hexane-ethanol (85:15, v/v) as the mobile phase and detection at 220 nm. The assay satisfies all of the criteria required for use in clinical pharmacokinetic studies.

Pharmacokinetic study of praziquantel administered alone and in combination with cimetidine in a single-day therapeutic regimen.

A brief therapeutic regimen of praziquantel, reduced to a single day, has been effective for treatment of neurocysticercosis. To study its pharmacokinetic characteristics, levels of praziquantel in plasma were determined for eight healthy volunteers after the administration of three oral doses of 25 mg/kg of body weight given at 2-h intervals, alone and with the simultaneous administration of cimetidine. Each volunteer received both regimens in a randomized crossover design. Blood samples were taken during a period of 12 h, and praziquantel concentration was measured by high-performance liquid chromatography. Levels of praziquantel in plasma remained above 300 ng/ml during a period of 12 h; they increased 100% when cimetidine was jointly administered. Compared with other regimens, the high levels obtained and the longer duration of action seem to be advantageous in prolonging the exposure of the parasites to the drug and support previous clinical experience showing that the treatment of neurocysticercosis with praziquantel can be reduced from 2 weeks to 1 day with the drug still retaining its cysticidal properties. Moreover, simultaneous administration of praziquantel and cimetidine could improve further the efficacy of the single-day therapy for cysticercosis and other parasitic diseases, such as schistosomiasis.

High-performance liquid chromatography determination of praziquantel enantiomers in human serum using a reversed-phase cellulose-based chiral stationary phase and disc solid-phase extraction.

A sensitive HPLC method for the quantification of praziquantel enantiomers in human serum is described. The method involves the use of a novel disc solid-phase extraction for sample clean-up prior to HPLC analysis and is also free of interference from trans-4-hydroxypraziquantel, the major metabolite of praziquantel. Chromatographic resolution of the enantiomers was performed on a reversed-phase cellulose-based chiral column (Chiralcel OJ-R) under isocratic conditions using a mobile phase consisting of 0.1 M sodium perchlorate-acetonitrile (66:34, v/v) at a flow-rate of 0.5 ml/min. Recoveries for R-(-)- and S-(+)-praziquantel enantiomers were in the range of 84-89% at 50-500 ng/ml levels. Intra-day and inter-day precisions calculated as R.S.D. were in the ranges of 3-8% and 1-8% for both enantiomers, respectively. Intra-day and inter-day accuracies calculated as percent error were in the 0.2-5% and 0.3-8% ranges for both enantiomers, respectively. Linear calibration curves were in the concentration range 10-600 ng/ml for each enantiomer in serum. The limit of quantification of each enantiomer was 10 ng/ml. The detection limit for each enantiomer in serum using a UV detector set at 210 nm was 5 ng/ml (S/N=2).

Prophylactic efficacy of clorsulon against Fasciola hepatica in calves and sheep.

A daily oral 5 mg kg-1 dose of clorsulon for 28 days in calves given Fasciola hepatica cysts at 3, 5, and 7 days after initiation of treatment was highly effective in reducing worm burdens (98%) and preventing liver pathology. In similarly infected and treated sheep, clorsulon showed little effect as a prophylactic for delaying the onset of liver pathology. The size of flukes recovered from treated sheep was reduced. Although clorsulon prevented development of fascioliasis in treated calves, the host antibody response was qualitatively similar to that of untreated infected calves, but the magnitude of the response was reduced. Blood clorsulon levels in calves rose to 2.90 micrograms ml-1 within the first week of treatment then fluctuated between 2.65 and 2.90 micrograms ml-1 for the next two weeks. Clorsulon levels in sheep were 0.50-0.60 micrograms ml-1 lower than those in calf blood. The difference in bioavailability of clorsulon between sheep and calves may have contributed to differences in efficacy of the drug.