Simultaneous pharmacokinetic modeling of a drug and two metabolites: application to albendazole in sheep

Albendazole pharmacokinetic parameters were determined in lambs after iv, oral, and intraruminal single administrations. The parent drug and two metabolites, albendazole sulfoxide and albendazole sulfone, were simultaneously determined in whole blood, plasma, and urine using an HPLC method. The parent drug was only recovered in plasma when injected intravenously. For other routes, only the two metabolites were detectable; they were present in red blood cells and plasma at equal concentrations. The pharmacokinetic parameters were determined by using compartmental models which simultaneously described the two oxidative steps and the urinary excretion of the sulfoxide derivative. Dose-dependent pharmacokinetics was studied in the dose range 0.95-3.8 mg/kg. The results showed that clearance remained constant within the tested dose range since the area under the curve normalized to the dose was similar in the cases of sulfoxide and sulfone metabolites, whatever the route of administration. The drug appeared to be extensively metabolized in the body regardless of the route of administration. Sulfoxidation probably took place in liver, but other tissues seemed to be responsible for the formation of the sulfoxide which has been described as the major anthelmintic derivative of albendazole.     

Effect of clotrimazole on microsomal metabolism and pharmacokinetics of albendazole

Albendazole is a broad spectrum anthelmintic drug widely used in human and veterinary medicine. Intestinal and hepatic albendazole metabolism leads to albendazole sulfoxide (active metabolite) and albendazole sulfone (inactive metabolite) formation. Microsomal sulfonase activity can be abolished by in-vitro interaction with clotrimazole and pharmacokinetic studies confirm this interaction. After albendazole incubation, albendazole sulfone formation was completely inhibited by 50 microM clotrimazole in intestinal incubations and a 50% inhibition was observed in hepatic incubations. The lower inhibition constant (K(i)) value observed in the intestinal incubations (9.4 +/- 1.0 microM) compared with the hepatic counterparts (23.3 +/- 15.8 microM) pointed to a greater affinity of the enzymatic systems in the intestine. Regarding the formation of albendazole sulfoxide, an inhibition close to 50% was observed in liver and intestine at 10 microM clotrimazole. The pharmacokinetic parameters obtained following the oral co-administration of albendazole sulfoxide and clotrimazole corroborated the in-vitro inhibition of albendazole sulfone formation, since the ratio of the area under the plasma concentration-time curves for the sulfoxide/sulfone (AUC(ABZSO)/AUC(ABZSO2)) was significantly higher (38.1%). In addition, the AUC and C(max) for albendazole sulfone were significantly lower. The effect of clotrimazole was also studied after prolonged treatment. Hepatic microsomal metabolism of albendazole was induced after 10 days of clotrimazole administration, with significant increases in formation of albendazole sulfoxide (40%) and sulfone (27%). These results offer further insight into the metabolism of benzimidazole drugs and highlight the difficulty involved in human therapy with these anthelmintics, since after prolonged treatment the drug interactions are affected differentially.     

抗棘球蚴药物研究：阿苯达唑代谢物及其类似物的合成

合成了共２５个阿苯达唑代谢物及其类似物。感染棘球蚴小鼠试验表明，其中７个化合物对细粒棘球蚴有较好的作用，而以阿苯达唑亚砜（１３）效果最好，治疗剂量仅为阿苯达唑的一半，抗小鼠继发生细粒棘球蚴病的疗效高于后者。另一个代谢物阿苯达唑砜则无杀虫作用。     

Albendazole causes stage-dependent developmental toxicity and is deactivated by a mammalian metabolization system in a modified zebrafish embryotoxicity test

The zebrafish embryotoxicity test has previously been combined with an external metabolic activation system (MAS) to assess developmental toxicity of metabolites produced by maternal metabolism. Due to toxicity of MAS the exposure was limited to one early and short period. We have modified the method and included additional testing time points with extended exposure durations. Using the anthelmintic drug albendazole as a model substance, we demonstrated stage-dependent toxic effects at three windows of zebrafish embryo development, i.e. 2-3, 12-14 and 24-28h post fertilization, and showed that MAS, by metabolic deactivation, reduced the toxicity of albendazole at all time points. Chemical analysis confirmed that albendazole was efficiently metabolized by MAS to the corresponding sulfoxide and sulfone, which are non-toxic to zebrafish embryos. To conclude, the modified zebrafish embryotoxicity test with MAS can be expanded for assessment of metabolites at different developmental stages.     

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.     

Analysis of albendazole metabolites by electrospray LC-MS/MS as a probe to elucidate electro-oxidation mechanism of albendazole

The electrochemical oxidation of albendazole was accomplished by controlled potential electrolysis technique. The oxidation was carried out in different pH solutions and yields the same products obtained by in vivo and in vitro metabolism, i.e. albendazole sulfoxide and albendazole sulfone. The identification of albendazole oxidation products was carried out by LC-MS/MS.     

The oxidative metabolism of aldicarb in pigs: in vivo-in vitro comparison

Aldicarb was administered (1 mg/kg b.w.) to four female pigs and the kinetics of its major oxidized metabolites (sulfoxide and sulfone) was followed for 6 hours. The in vitro transformations of the carbamate pesticide into these two still active metabolites were also investigated in hepatocytes and in microsomes from pig livers. In all cases, aldicarb was quickly oxidized to the sulfoxide (major metabolite) and only a minor quantity of sulfone was produced. The in vivo toxic symptomatology was related to the peak serum concentration of sulfoxide, suggesting that this metabolite is principally responsible for the aldicarb toxicity. Selective in vitro inhibition of flavin-containing and cytochrome P-450 monooxygenases confirmed that the former enzymes catalyze mainly sulfoxide production whereas the latter that of sulfone.     

Relative inhibitory potency of molinate and metabolites with aldehyde dehydrogenase 2: implications for the mechanism of enzyme inhibition

Molinate is a thiocarbamate herbicide used as a pre-emergent in rice patty fields. It has two predominant sulfoxidation metabolites, molinate sulfoxide and molinate sulfone. Previous work demonstrated an in vivo decrease in liver aldehyde dehydrogenase (ALDH) activity in rats treated with molinate and motor function deficits in dogs dosed chronically with this compound. ALDH is an enzyme important in the catabolism of many neurotransmitters, such as dopamine. Inhibition of this enzyme may lead to the accumulation of endogenous neurotoxic metabolites such as 3,4-dihydroxyphenylacetaldehyde, a dopamine metabolite, which may account for the observed neurotoxicity. In this study, the relative reactivity of molinate and both of its sulfoxidation metabolites toward ALDH was investigated, as well as the mechanism of inhibition. The ALDH activity was monitored in two different model systems, human recombinant ALDH (hALDH2) and mouse striatal synaptosomes. Molinate sulfone was found to be the most potent ALDH inhibitor, as compared to molinate and molinate sulfoxide. The reactivity of these three compounds was also assessed, using N-acetyl Cys, model peptides, and hALDH2. It was determined that molinate sulfone is capable of covalently modifying Cys residues, including catalytic Cys302 of ALDH, accounting for the observed enzyme inhibition.     

Pharmacokinetic interaction between albendazole sulfoxide enantiomers and antiepileptic drugs in patients with neurocysticercosis

The aim of the present investigation was to determine the interaction between the antiepileptic drugs (AEDs) phenytoin, carbamazepine, and phenobarbital and the enantioselective metabolism of albendazole. Thirty-two adults with a diagnosis of the active form of intraparenchymatous neurocysticercosis and treated with albendazole at the dose of 7.5 mg/kg every 12 hours for 8 days were studied. The patients were divided into four groups based on the combined use of AEDs or not: control group (n = 9), phenytoin group (n = 9 patients treated with 3-4 mg/kg/d sodium phenytoin), carbamazepine group (n = 9 patients treated with 10-20 mg/kg/d carbamazepine), and phenobarbital group (n = 5 patients treated with 1.5-4.5 mg/kg/d phenobarbital). Serial blood collections were carried out on day 8 of albendazole treatment during the last 12-hour dose interval. Plasma concentrations of the (+)- and (-)-albendazole sulfoxide (ASOX) and albendazole sulfone (ASON) metabolites were determined by high-performance liquid chromatography using a chiral phase column and fluorescence detection. The pharmacokinetic parameters were analyzed by analysis of variance followed by the Tukey-Kramer test. The results are reported as means. The following differences (P < 0.05) were observed between the control and the phenytoin, carbamazepine, and phenobarbital groups, respectively: (+)-ASOX area under the concentration-time curve for 0 to 12 hours after treatment (AUC(0-12)) 6.1, 2.1, 3.1, 2.4 microg/h/mL; (+)-ASOX maximum plasma concentration (C(max)) 0.8, 0.3, 0.4, 0.3 microg/mL; (+)-ASOX half-life (t1/2) 8.0, 3.8, 4.1, 4.9 h; (-)-ASOX AUC(0-12) 1.8, 0.4, 0.6, 0.5 microg/h/mL; (-)-ASOX C(max) 0.2, 0.06, 0.1, 0.1 microg/mL; (-)-ASOX (t(1/2)) 4.3, 1.9, 2.2, 2.1 h; ASON AUC(0-12) 0.5, 0.2 microg/h/mL; ASON C(max) 0.8, 0.3, 0.4, 0.3 microg/mL; ASON (t(1/2)) 8.0, 3.8, 4.1 h. The results show that phenytoin, carbamazepine, and phenobarbital induce to approximately the same extent the oxidative metabolism of albendazole in a nonenantioselective manner. Notably, a significant reduction in the plasma concentration of the active ASOX metabolite was observed in patients with neurocysticercosis treated with these AEDs.     

Absorption and metabolism of albendazole after intestinal ischemia/reperfusion.

Pathophysiological processes involving inflammatory response may affect absorption and biotransformation of some drugs, modifying their pharmacokinetic behaviour. Ischemia/reperfusion (I/R) injury has been used as a model for inflammatory processes. The aim of this work was to study the effect of intestinal I/R injury on the absorption and metabolism processes of one orally administered drug, albendazole that is anthelmintic drug, it undergoes intestinal bioconversion into albendazole sulfoxide by two enzymatic systems, cytochromes P450 (CYP450) and flavin-containing monooxygenase (FMO). Male Wistar rats were used to study the influence of I/R in the intestinal absorption and metabolism of albendazole, after 60 min of mesenteric occlusion and 30 min of reperfusion. The intestinal studies were performed in microsomal, and everted ring incubations. During in situ studies, the I/R group had faster disappearance of albendazole from the lumen. In addition, albendazole only appeared in blood samples of the I/R group, while albendazole sulfoxide appeared in both samples and was higher in the control group. These findings are supported by significant reductions of albendazole sulfoxide formation in intestinal everted ring assays and in microsomal incubations after the I/R process. Both metabolizing systems, CYP4503A and FMO, were affected by I/R. Our data indicate that I/R injury, considered as an inflammatory model, reduces absorption and metabolism processes of albendazole.