Ex Vivo Anthelmintic Activity of Albendazole-Sulphoxide Enantiomers

In vivo exposure of Albendazole sulphoxide by Haemonchus contortus and correlation between plasma and target tissue or gastrointestinal content dispositions in goats

Sheep and goats are sharing different helminth parasites including Haemonchus contortus. Control of these helminths is based mainly on the use of anthelmintics. However, in goats, the application of anthelmintics is often carried out mainly at dosages determined for sheep without knowing the real effects and metabolism features. One of the several anthelmintic classes used against these parasites is (pro) benzimidazoles which are still widely in use in small ruminants in many countries. The objective of this study was to determine (i) the correlation between plasma and tissue or gastrointestinal content dispositions of ricobendazole (RBZ) in goats and (ii) the in vivo exposure of ricobendazole by H. contortus. Ten goats were experimentally infected with 10,000 larvae of H. contortus. Four weeks of post-infection, the animals received RBZ subcutaneously at 5 mg/kg body weight. Two goats were sacrificed per time at 1, 2, 4, 6 and 12 h after drug administration and, blood, bile, urine, liver, lung, muscle and kidney gastrointestinal tissues/fluids were collected. Adult H. contortus were collected from abomasum, and all samples were analysed by HPLC system. Ricobendazole (RBZ) and its sulphone metabolite were extensively excreted by urine and distributed to all tissues and digestive tract, mainly into the abomasum fluid. RBZ concentration in the lung and ABZSO₂ in the kidney were relatively higher than those of other tissues, respectively. The parent drug and its metabolite were recovered in both male and female H. contortus. This study indicates that in goats the plasma concentration profiles of RBZ are strongly correlated with those achieved in different target tissues or fluids, which in turn, reflect the amount of drug taken up by parasites.

Pharmacokinetics, Activity, and Residue Elimination of R- and S-Diclazuril in Broiler Chickens

Diclazuril (DIC) is widely used as a racemic mixture to prevent and treat coccidiosis in farm animals, while the pharmacokinetics, bioactivity, and toxicity of DIC enantiomers are not known at all. This study first established a simple, sensitive, and reliable liquid chromatography tandem mass spectrometry method for separation of R-DIC and S-DIC and their analyses. Then, it was applied to investigate the stereoselective pharmacokinetics and residual elimination of individual enantiomers, and their anticoccidial activity was also evaluated in broiler chickens. The results indicated that the area under the concentration-time curve (AUC) and elimination half-life (t_1/2β) were significantly different (p < 0.05) for two enantiomers in chicken plasma. The AUC and t_1/2β of S-DIC were approximately 2 and 1.4 times those of R-DIC, respectively. The residual elimination of DIC enantiomers in chicken tissues was also stereoselective. The concentrations of S-DIC in chicken muscle and liver were greater than those of R-DIC, and it is the opposite in the kidney. There was no significant difference (p > 0.05) in the anticoccidial activity of racemate and enantiomers when a single enantiomer in feed was added above 0.5 mg kg^-1. However, the anticoccidial activity of R-DIC (0.25 mg kg^-1) was significantly higher (p < 0.05) than that of S-DIC (0.25 mg kg^-1) in the diet. It should be mentioned that in chicken small intestine and cecum, the enantiomerization rate of each enantiomer in the infection group was faster than that in the uninfected group.

Efficacy of novel albendazole salt formulations against secondary cystic echinococcosis in experimentally infected mice

In this study, we evaluated the efficacy, expressed as a mean weight decrease of the whole echinococcal cyst mass, of novel benzimidazole salt formulations in a murine Echinococcus granulosus infection model. BALB/c mice were intraperitoneally infected with protoscoleces of E. granulosus (genotype G1). At 9 months post-infection, treatment with albendazole (ABZ), ricobendazole (RBZ) salt formulations, and RBZ enantiomer salts (R)-(+)-RBZ-Na and (S)-(-)-RBZ-Na formulations were initiated. Drugs were orally applied by gavage at 10 mg kg-1 body weight per day during 30 days. Experimental treatments with benzimidazole sodium salts resulted in a significant reduction of the weight of cysts compared to conventional ABZ treatment, except for the (S)-(-)-RBZ-Na enantiomer formulation. Scanning electron microscopy and histological inspection revealed that treatments impacted not only the structural integrity of the parasite tissue in the germinal layer, but also induced alterations in the laminated layer. Overall, these results demonstrate the improved efficacy of benzimidazole salt formulations compared to conventional ABZ treatment in experimental murine cystic echinococcosis.

Comparative pharmacokinetics and bioavailability of albendazole sulfoxide in sheep and goats, and dose-dependent plasma disposition in goats

Background

The aims of this study were to compare the pharmacokinetics of albendazole sulfoxide (ABZ-SO, ricobendazole) in goats and sheep at a dose of 5 mg/kg bodyweight (BW), after intravenous (IV) and subcutaneous (SC) administrations, and to investigate the effects of increased doses (10 and 15 mg/kg BW) on the plasma disposition of ABZ-SO in goats following SC administration. A total of 16 goats (Capra aegagrus hircus, eight males and eight females) and 8 sheep (Ovis aries, four males and four females) 12–16 months old and weighing 20–32 kg, were used. The study was designed according to two-phase crossover study protocol. In Phase-1, eight sheep were assigned as Group I and 16 goats were allocated into two groups (Group II and Group III). ABZ-SO was applied to Group I (sheep) and Group II (goats) animals subcutaneously, and to Group III (goats) animals intravenously, all at a dose rate of 5 mg/kg BW. In Phase-2, the sheep in the Group I received ABZ-SO intravenously in a dose of 5 mg/kg BW; the goats in Group II and Group III received ABZ-SO subcutaneously at a dose of 10 mg/kg and 15 mg/kg BW, respectively. Blood samples were collected from the jugular vein at different times between 1 and 120 h after drug administrations. The plasma concentrations of ABZ-SO and its metabolites were analysed by high performance liquid chromatography.

Results

In goats, the area under the curve, terminal half-life and plasma persistence of ABZ-SO were significantly smaller and shorter, respectively, compared with those observed in sheep following both IV and SC administrations at a dose of 5 mg/kg BW. On the other side, dose-dependent plasma dispositions of ABZ-SO were observed following SC administration at increased doses (10 and 15 mg/kg) in goats.

Conclusions

Consequently, ABZ-SO might be used at higher doses to provide higher plasma concentration and thus to achieve greater efficacy against the target parasites.

In vitro analysis of albendazole sulfoxide enantiomers shows that (+)-(R)-albendazole sulfoxide is the active enantiomer against Taenia solium

Albendazole is an anthelmintic drug widely used in the treatment of neurocysticercosis (NCC), an infection of the brain with Taenia solium cysts. However, drug levels of its active metabolite, albendazole sulfoxide (ABZSO), are erratic, likely resulting in decreased efficacy and suboptimal cure rates in NCC. Racemic albendazole sulfoxide is composed of ABZSO (+)-(R)- and (-)-(S) enantiomers that have been shown to differ in pharmacokinetics and activity against other helminths. The antiparasitic activities of racemic ABZSO and its (+)-(R)- and (-)-(S) enantiomers against T. solium cysts were evaluated in vitro. Parasites were collected from naturally infected pigs, cultured, and exposed to the racemic mixture or to each enantiomer (range, 10 to 500 ng/ml) or to praziquantel as a reference drug. The activity of each compound against cysts was assayed by measuring the ability to evaginate and inhibition of alkaline phosphatase (AP) and parasite antigen release. (+)-(R)-ABZSO was significantly more active than (-)-(S)-ABZSO in suppressing the release of AP and antigen into the supernatant in a dose- and time-dependent manner, indicating that most of the activity of ABZSO resides in the (+)-(R) enantiomer. Use of this enantiomer alone may lead to increased efficacy and/or less toxicity compared to albendazole.

Enantiomerical pharmacokinetic prevalence of (+) albendazole sulphoxide in Trichinella spiralis muscle larvae

In a previous work, it was demonstrated that (+) albendazole sulphoxide (SOABZ) has higher anthelmintic activity than (-) SOABZ (Bolás-Fernández et al. J Parasitol 90:407-409, 2004). In this work, the pharmacokinetics characteristics of SOABZ and its enantiomeric forms were studied in an ex vivo model system for Trichinella spiralis isolated muscle larvae. To this end, samples of either racemic or purified SOABZ enantiomers were added to the incubation medium. Quantification of either albendazole, racemic SOABZ or its enantiomers was performed by validated HPLC methods and the effect of different SOABZ concentrations in relation to time of contact with the larvae was also analysed. Obviously, higher concentration of SOABZ in the medium leads to higher concentrations of SOABZ inside the larvae which increased in an exponential mode, thus indicating a simple diffusion process. At least 18 h of contact with the drug was required to achieve anthelmintic effects. Besides, after this time, the concentration of (+) SOABZ inside the larvae was significantly higher than that of the (-) SOABZ. From these results, it can be concluded that the higher activity found in the previous work is clearly related to the pharmacokinetic prevalence of (+) enantiomer inside the larvae.

Albendazole-praziquantel interaction in healthy volunteers: kinetic disposition, metabolism and enantioselectivity

AIM

This study investigated the kinetic disposition, metabolism and enantioselectivity of albendazole (ABZ) and praziquantel (PZQ) administered alone and in combination to healthy volunteers.

METHODS

A randomized crossover study was carried out in three phases (n= 9), in which some volunteers started in phase 1 (400 mg ABZ), others in phase 2 (1500 mg PZQ), and the remaining volunteers in phase 3 (400 mg ABZ + 1500 mg PZQ). Serial blood samples were collected from 0-48 h after drug administration. Pharmacokinetic parameters were calculated using a monocompartmental model with lag time and were analyzed using the Wilcoxon test; P ≤ 0.05.

RESULTS

The administration of PZQ increased the plasma concentrations of (+)-ASOX (albendazole sulphoxide) by 264% (AUC 0.99 vs. 2.59 µg ml(-1) h), (-)-ASOX by 358% (0.14 vs. 0.50 µg ml(-1) h) and albendazole sulfone (ASON) by 187% (0.17 vs. 0.32 µg ml(-1) h). The administration of ABZ did not change the kinetic disposition of (+)-(S)-PZQ (-)-(R)-4-OHPZQ or (+)-(S)-4-OHPZQ, but increased the plasma concentration of (-)-(R)-PZQ by 64.77% (AUC 0.52 vs. 0.86 µg ml(-1) h).

CONCLUSIONS

The pharmacokinetic interaction between ABZ and PZQ in healthy volunteers was demonstrated by the observation of increased plasma concentrations of ASON, both ASOX enantiomers and (-)-(R)-PZQ. Clinically, the combination of ABZ and PZQ may improve the therapeutic efficacy as a consequence of higher concentration of both active drugs. On the other hand, the magnitude of this elevation may represent an increased risk of side effects, requiring, certainly, reduction of the dosage. However, further studies are necessary to evaluate the efficacy and safety of this combination.

Pharmacological assessment of netobimin as a potential anthelmintic for use in horses: plasma disposition, faecal excretion and efficacy

This study aimed to determine the plasma disposition and faecal excretion of netobimin (NTB) and its respective metabolites as well as the efficacy against strongyles in horses following oral administration. Netobimin (10mg/kg) was administered orally to 8 horses. Blood and faecal samples were collected from 1 to 120h post-treatment and analysed by high performance liquid chromatography (HPLC). Using a chiral phase-based HPLC, plasma disposition of ABZSO enantiomers produced was also determined. Faecal strongyle egg counts (EPG) were performed by a modified McMaster's technique before and after the treatment. Neither NTB nor ABZ were present and only albendazole sulphoxide (ABZSO) and sulphone metabolites (ABZSO(2)) were detected in the plasma samples. Maximum plasma concentration of ABZSO (0.53+/-0.14microg/ml) and ABZSO(2) (0.36+/-0.09microg/ml) were observed at (t(max)) 10.50 and 19.50h, respectively following administration of NTB. The area under the curve (AUC) of the two metabolites was similar to each other. Netobimin was not detected, and ABZ was predominant in faecal samples. The maximum plasma concentration (C(max)) of (-)ABZSO was significantly higher than (+)ABZSO, but the area under the curves (AUCs) of the enantiomer were not significantly different each other in plasma samples. The enantiomers of ABZSO were close to racemate in the faecal samples analyzed. Netobimin reduced the EPG by 100%, 100%, 77%, 80% and 75% 2, 4, 6, 8 and 10 weeks post-treatment, respectively. The specific behaviour of the two enantiomers probably reflects different enantioselectivity of the enzymatic systems of the liver which are responsible for sulphoxidation and sulphonation of ABZ. Considering the pharmacokinetic and efficacy parameters NTB could be used as an anthelmintic in horses.

Pharmacokinetics of albendazole sulfoxide enantiomers administered in racemic form and separately in rats

The pharmacokinetic behaviour of albendazole sulfoxide (ABZSO) enantiomers was studied in rats after the oral administration of 10 mg/kg of rac-ABZSO, 5 mg/kg of (-)-ABZSO or 5 mg/kg of (+)-ABZSO. The disposition profiles of ABZSO enantiomers were similar in all treatments, but the calculated area under the curve for the (-)-ABZSO was higher in all cases compared with (+)-ABZSO. The results suggest that there is no chiral inversion of ABZSO enantiomers. After the administration of rac-ABZSO, 17.2% of the total dose was recovered in urine as albendazole ABZ (0.1%), albendazole sulfone ABZSO(2) (0.3%), albendazole 2-aminosulfone (ABZ-SO(2)NH(2)) (3.1%) and ABZSO (13.7%). The ratio (+) to (-) was similar in urine (1.6) and blood (1.7).

Liver microsomal biotransformation of albendazole in deer, cattle, sheep and pig and some related wild breeds

Albendazole (ABZ) biotransformation was studied in vitro in liver microsomes of adult noncastrated male farm animals (ram, buck, bull and boar), castrated adult males (wether, billy and hog), and free living males (fallow buck, red deer stag, mouflon ram, roe buck and wild boar). Liver microsomal fractions were incubated with either ABZ or racemic albendazole sulphoxide (ABZSO). ABZ was extensively metabolized to the (+) and (-) enantiomers of ABZSO, whereas ABZSO underwent a slow oxidation to albendazole sulphone (ABZSO2) in all species. In all species both ABZSO enantiomers were detected. The chiral ratio, (+)-ABZSO/(-)-ABZSO, was greater than one in farm animals, mouflon and wild boar, and less than one in three species of deer. For total ABZ sulphoxidation, deer like species had lower values compared to the other species. Mouflon ram and ram had lower total sulphoxidation rates compared to wethers, as well as ABZ suphoxidation towards (+)-ABZSO. No significant difference occurred comparing ABZSO formation in mouflon ram and ram, but ABZSO2 formation rate in mouflon ram was higher than in rams and wethers. Roe deer stag, fallow buck and red deer stag did not differ in both total-ABZSO and (-)-ABZSO synthesis rates and roe deer stag and fallow buck did not differ in synthesis rates of (+)-ABZSO and ABZSO2. The bull differed from other species in all metabolites studied, except for red deer stag and boar in (-)-ABZSO synthesis rate. The extent of ABZSO sulphonation to ABZSO2 in bull microsomes was more than twice that of other species.