Pharmacokinetics and metabolism of fenbendazole in channel catfish

Pharmacokinetics and therapeutic efficacies of fenbendazole in comparison with levamisole in helminth-infected Caspian turtles (Mauremys caspica)

The pharmacokinetics and bioavailability of fenbendazole and levamisole were determined in Caspian turtles after a single intravenous (i.v.) and subcutaneous (s.c.) administration. Thirty turtles diagnosed as naturally infected with Serpinema microcephalus and Falcaustra armenica nematodes received fenbendazole (50 mg/kg) or levamisole (10 mg/kg) by i.v. and s.c. administrations. Blood samples were collected at time 0, 0.125, 0.25, 0.5, 1, 2, 4, 8, 12, 24, and 48 h after drug administration. Plasma drug concentrations were determined by a validated high-performance liquid chromatography method. Data were analyzed by noncompartmental methods. The mean elimination half-life of levamisole was 5.16 h and 12.03 h for i.v. and s.c. routes, respectively, and for fenbendazole, the mean elimination half-life was 25.38 h (i.v.) and 29.77 h (s.c.). The total clearance and volume of distribution at steady-state for levamisole and fenbendazole following i.v. administration were 0.22, 0.44 ml/g/h, and 1.06 and 7.35 ml/g, respectively. For the s.c. route, the peak plasma concentration of levamisole and fenbendazole was 10.53 and 5.24 μg/mL, respectively. The s.c. bioavailability of levamisole and fenbendazole was complete. Considering high anthelmintic efficacy and bioavailability after s.c. administration of levamisole and fenbendazole, and the absence of adverse effects, this route of administration is an easy and efficacious way of treating nematodes in Caspian turtles.

Untargeted metabolomics-assisted comparative cytochrome P450-dependent metabolism of fenbendazole in human and dog liver microsomes

Fenbendazole (FBZ), a benzimidazole carbamate anthelmintic, has attracted attention for its antitumor activity. This study examined the metabolic characteristics of FBZ in humans compared with those in dogs. The phase I metabolites were identified in liver microsomal incubates using liquid chromatography-mass spectrometry (MS)-based untargeted metabolomics approaches. Seven metabolites of FBZ were identified by principal component analysis and orthogonal partial least square-discriminant analysis based on the global ion variables of the FBZ incubation groups. The chemical structure of the FBZ metabolites was suggested by examining the MS/MS spectrum and isotope distribution pattern. Cytochrome P450 (CYP) 1A1, CYP2D6, and CYP2J2 were the major isozymes responsible for the FBZ metabolism. No differences in the types of metabolites produced by the two species were noted. Multivariate analysis of human and dog incubation groups showed that five metabolites were relatively abundant in humans and the other two were not. In summary, the phase I metabolic profile of FBZ and the comparative metabolism between humans and dogs were examined using an untargeted metabolomics approach. This study suggests a successful investigation of FBZ metabolism in humans for conducting safety assessments regarding drug repositioning.

Plasma concentrations of fenbendazole (FBZ) and oxfendazole in alpacas (Lama pacos) after single intravenous and oral dosing of FBZ

The objective of this study was to determine plasma pharmacokinetics and bioavailability of fenbendazole (FBZ) and oxfendazole (OFZ) after intravenous (iv) and oral administrations of FBZ (5 mg/kg) to alpacas. Plasma concentrations of FBZ and OFZ after administration of FBZ iv and orally (5 mg/kg) were determined by high-performance liquid chromatography with ultraviolet detection. Total clearance (CL) of FBZ was 16.5±4 mL/kg/min (range: 4–31 mL/kg/min), and steady-state volume of distribution (Vd_ss) was 3.3±1 L/kg (range: 1.7–7.4 L/kg). The terminal phase half-life of FBZ after iv administration was 5.9±3.8 hours (range: 0.8–20 hours). After oral administration, the FBZ terminal phase half-life was 23±5 hours (range: 9–37 hours) and the systemic bioavailability of FBZ was 16%±6% (range: 1%–41%). Peak FBZ concentrations after oral administration were 0.13±0.05 µg/mL (range: 0.05–0.28 µg/mL) at 10 hours (range: 8–12 hours). Peak plasma OFZ concentrations after oral dosing with FBZ (5 mg/kg) were 0.14±0.05 µg/mL (0.05–0.3 µg/mL) at 24±7 hours (range: 12–48 hours). FBZ clearance is lower in comparison to that of other species. Systemic availability of FBZ after oral administration is low after oral dosing. Metabolites of FBZ produced by alpacas are similar to those observed in other species.

Metabolism and depletion of albendazole in the muscle tissue of channel catfish following oral treatment

The residue depletion of albendazole (ABZ) and its metabolites was studied in channel catfish muscle tissue. Channel catfish were dosed once with 10 mg/kg ABZ via stomach tube with manual restraint. Muscle tissue samples were collected at 8, 16, 24, 48, 72, 96 and 120 h postdose. A high-performance liquid chromatographic method was used to assay ABZ and its major metabolites: ABZ sulfoxide (ABZ-SO), ABZ sulfone (ABZ-SO2) and ABZ aminosulfone (ABZ-2-NH2SO2) in the muscle tissue. The results indicate that ABZ and ABZ-SO were present in low concentrations, i.e. <15 and <10 microg/kg, respectively, at 8 h postdose in catfish muscle with and without skin. ABZ-SO2 was present at 1 microg/kg concentration levels until 48 h in muscle alone and 72 h in muscle with skin. ABZ-2-NH2SO2 was not detected at any withdrawal periods.

Metabolism and residue depletion of albendazole and its metabolites in rainbow trout, tilapia and Atlantic salmon after oral administration

Metabolic and residue depletion profiles of albendazole (ABZ) and its major metabolites in three fish species, rainbow trout, tilapia and Atlantic salmon are reported. Based on these profiles, similarities (or dissimilarities) between species will determine the potential to group fish species. ABZ at 10 mg/kg body weight was incorporated into fish food formulated in a gelatin base or in gel capsule and fed as a single dose to six fish from each species. Rainbow trout were held three each in a partitioned 600-L tank. Tilapia and Atlantic salmon were housed in separate 20-L tanks. Samples of muscle with adhering skin were collected at 8, 12, 18, 24, 48, 72, and 96 h postdose from trout kept at 12 degrees C, at 4, 8, 12, 24, 48, 72, 96, 120, and 144 h postdose from tilapia kept at 25 degrees C and at 8, 14, 24, 48, 72, and 96 h postdose from Atlantic salmon kept at 15 degrees C. The samples were homogenized in dry ice and subjected to extraction and cleanup procedures. The final extracts were analyzed for parent drug ABZ and its major metabolites, albendazole sulfoxide (ABZ-SO), albendazole sulfone (ABZ-SO2) and albendazole aminosulfone using high-performance liquid chromatography with fluorescence detection. ABZ was depleted by 24 h in trout and tilapia and by 48 h in salmon; ABZ-SO, a pharmacologically active metabolite, was depleted by 48 h in tilapia, by 72 h in rainbow trout and was present until 96 h in salmon; and low levels of ABZ-SO2 and albendazole aminosulfone, both inactive metabolites, were detectable at least till 96 h in all three fish species.