Two high-performance liquid chromatographic determinations for mebendazole and its metabolites in human plasma using a rapid Sep Pak C18 extraction

Fenbendazole as a method for measuring supplement intake in grazing sheep

Currently there is a need for an accurate and non-hazardous method to measure individual intake of a supplement in grazing sheep over a prolonged period. This paper examines the potential of fenbendazole (FBZ) as a marker of intake. The following five experiments aim to determine the relationship between oral ingestion of FBZ and the plasma concentrations of FBZ and its metabolites oxfendazole (OFZ) and FBZ-sulfone (SUL) after single, multiple and daily doses both in housed and grazing sheep and sheep infected with internal parasites. The results from these experiments indicate that OFZ+SUL concentrations in plasma are dependent on FBZ dose rate in housed and grazing animals with differences evident between different dose rates (P < 0.001). Variability of OFZ and SUL concentrations increase in grazing compared with housed animals. Area under the curve of metabolite concentrations was also shown to indicate dose rate regardless of the timing and frequency of dose. Stepwise regressions indicated that sampling every 48 h gave a good representation of area under the curve for different dose rates (R2 = 0.951, P < 0.001). A significant separation of treatment means was achieved when samples were taken every 48 h and pooled during daily dosing with FBZ (P < 0.001). Finally gastrointestinal nematode infection did not affect OFZ and SUL concentrations after daily doses of FBZ. The results from these experiments indicate that FBZ is a useful and accurate marker of supplement intake in grazing animals.

Review of methodology for the determination of benzimidazole residues in biological matrices

Benzimidazoles are anthelmintic agents widely used in the treatment of parasitic infections in a range of species and as fungicidal agents in the control of spoilage of crops during storage and transport. In this paper, the more important benzimidazoles are introduced and their pharmacological effects and physiochemical properties discussed. The metabolism of these drugs is described relating to the occurrence and persistence of residues in biological matrices, providing information for selection of suitable matrices and target residues for testing. Methods for determination of benzimidazoles are reviewed for a range of biological matrices. The importance of selecting suitable extraction and clean-up procedures is discussed, along with the difficulties encountered in adapting single residue methods to multi-residue methods. The importance of suitable detection systems for determination of benzimidazoles, namely, screening, HPLC, GC and confirmatory methods is described in detail. The future for benzimidazole residue analysis is discussed, focusing on selection of appropriate residues for screening methods and protocols for confirmation of benzimidazole residues.

Dual-mode gradient HPLC procedure for the simultaneous determination of chloroquine and proguanil

In order to assay the antipaludic capsule of the Service de Santé des Armées (SSA), that contains two antimalarial drugs, i.e. chloroquine sulfate (CQS, cp1) and proguanil hydrochloride (PGH, cp5), a HPLC procedure was developed. A reversed-phase ion-pair high-performance liquid chromatography (HPLC) method with an ultraviolet detection at 254 nm was set up and validated. Elution system includes programming of both organic concentration and flow-rate known as 'dual-mode gradient'. This method allows the simultaneous determination of both active compounds and separation of four process related substances. The method is simple, rapid, selective and accurate, and the precision is good with an inter- and intra-assay of <2%. The sensitivity is particularly suitable for pharmaceutical quality control.

High-performance liquid chromatographic separation and determination of the process related impurities of mebendazole, fenbendazole and albendazole in bulk drugs

Simple, specific and rapid reversed-phase high-performance liquid chromatographic methods to separate and determine potential impurities of anthelmintic drugs viz., mebendazole, fenbendazole and albendazole are reported. These methods afforded efficient separation, good resolution and identification of all the impurities examined. The methods were successfully applied not only for quality assurance, but also process development of the select anthelmintic drugs.

Micellar electrokinetic capillary chromatography for the determination of Viagra and its metabolite (UK-103,320) in human serum

Micellar electrokinetic capillary chromatography (MEKC) was investigated for the determination of Viagra (sildenafil citrate, SC) and its metabolite (UK-103,320) in human serum in a concentration range of clinical interest. For MEKC, human serum samples spiked with SC and UK were obtained directly after elution with methanol from a tC18 cartridge. The extract was evaporated and regenerated in a solution 1 mM of phosphate buffer (pH 12.3) which contained a methanol percentage of 20% that was analyzed using phosphate buffer (pH 12.3, 10 mM) containing 30 mM sodium dodecyl sulfate (SDS) as separation electrolyte and a fused-silica capillary. This method gave satisfactory interday precision with respect to migration times relative standard deviation (RSD < 1%) and linear responses for the concentration ranges investigated (0.50-3.50 mg L(-1) for the compound SC and 0.90-4.60 mg L(-1) for UK). An intraday RSD (n = 5 graphs) between the slopes of the calibration graphs was acceptable (6.40%) for SC and (3.37%) for UK. A satisfactory interday precision between slopes was also obtained (RSD 4.10% for SC and a RSD 2.72% for UK) which demonstrated the ruggedness of this method. Detection limits (S/N = 3) were about 200 ng/mL for both compounds in human serum. MEKC was shown as a good method with regards to simplicity, precision and sensitivity.

High-performance liquid chromatographic profiling of indolylacryloylglycine and its possible precursors in body fluids

Indolylacryloylglycine (IAcrGly) is one of the physiological components of urine, although its source and its role in the human organism have not yet been unambiguously established. Changes in the IAcrGly excretion level have been found under some physiological (age dependence, seasonal variations) and pathological (photodermatoses, muscle dystrophy, liver cirrhosis) conditions. The proposed method for IAcrGly, indolylacrylic acid and its possible precursors, namely indolyllactic and indolylpropionic acids, involves deproteinization and extraction of urine on a Sep Pak C18 cartridge. HPLC analysis was carried out using a DataApex liquid chromatograph, equipped with an LCD 2082 UV detector, signals being acquired with a CSW workstation. The chromatographic column was Spherisorb ODS, 5 microns (125 x 4 mm I.D.), the mobile phase for isocratic elution was ethanol-1% acetic acid (27:73) and the flow-rate was 0.7 ml/min. The lower response limit is about 1 mumol/l for all metabolites at 280 nm.

High-performance liquid chromatographic determination of the silicon phthalocyanine Pc 4 in human blood

A sensitive and reproducible method has been developed for the measurement of the silicon phthalocyanine Pc 4 in red blood cell concentrates (RBCC). The procedure involves extraction of the RBCC with acetonitrile, purification of the extracts with reversed-phase Sep-Pak C18 cartridges and determination of Pc 4 in the extracts by high-performance liquid chromatography (HPLC) using a reversed-phase C18 column. The detection limit with 1-ml RBCC samples is 2 ng. This method is applicable to monitoring Pc 4 during its use as a photosensitizer for the inactivation of viruses in RBCC prior to transfusion. It has the potential to be adapted for measuring Pc 4 in tissues during its use in photodynamic therapy of cancer.

Benzimidazoles, potent anti-mitotic drugs: substrates for the P-glycoprotein transporter in multidrug-resistant cells

P-glycoprotein is though to mediate the energy-dependent efflux of many structurally and functionally unrelated lipophilic compounds. Presently, the molecular mechanism underlying the binding and efflux of drugs by P-glycoprotein is not well understood. However, it has been suggested that two planar benzene ring structures and a cationic charge are commonly found in many drugs that interact with P-glycoprotein. The benzimidazoles (BZs) are potent anti-tumour, anti-fungal and anti-parasitic agents, whose mode of action is thought to result from their inhibition of microtubule functions. Although other classes of microtubule inhibitors, such as colchicine and vinblastine, have been studied extensively with respect to their interaction and efflux by P-glycoprotein, the BZ group of drugs has not been characterized. In this study, we have characterized the interaction of BZ with multidrug-resistant cells and found that resistant cells accumulated substantially less BZ compared with drug-sensitive cells. Furthermore, BZ was more toxic to sensitive than to drug-resistant cells, suggesting that BZ is likely to be a substrate for the P-glycoprotein drug efflux pump. In addition, we used a photoactive analogue of BZ ([125I]ASA-BZ) to demonstrate a direct binding between BZ and P-glycoprotein. Results showing that a molar excess of vinblastine, unmodified BZ, verapamil and rhodamine 123, but not colchicine, inhibited the photoaffinity labelling of P-glycoprotein by [125I]ASA-BZ confirmed the binding specificity of BZ to P-glycoprotein. Protease digestion of [125I]ASA-BZ photoaffinity labelled P-glycoprotein yielded two peptides that were similar to those obtained with other P-glycoprotein-associated drugs, e.g. azidopine and iodoaryl azidoprazosin. Taken together, these results demonstrate a direct and specific interaction between P-glycoprotein and BZ in a manner that is probably similar to other previously characterized P-glycoprotein-associated drugs.

Determination of a new antifilarial drug, UMF-058, and mebendazole in whole blood by high-performance liquid chromatography

A rapid and selective high-performance liquid chromatographic assay for simultaneous quantitative determination of a new antifilarial drug (UMF-058, I) and mebendazole (MBZ) is described. After a simple extraction from whole blood, both compounds were analysed using a C18 Nova Pak reversed-phase column and a mobile phase of methanol-0.05 M ammonium dihydrogenphosphate (50:50, v/v) adjusted to pH 4.0, with ultraviolet detection at 291 nm. The average recoveries of I and MBZ over a concentration range of 25-250 ng/ml were 92.0 +/- 7.7 and 84.4 +/- 4.4%, respectively. The minimum detectable concentrations in whole blood for I and MBZ were 7 and 6 ng/ml, respectively. This method was found to be suitable for pharmacokinetic studies.

High-performance liquid chromatographic determination of the anthelmintic mebendazole in eel muscle tissue

A simple high-performance liquid chromatographic method for the determination of mebendazole in eel muscle tissue was developed. It is applicable for concentrations of 10 micrograms/kg and higher. Muscle tissue was extracted with ethyl acetate, and the extract, after addition of hexane, was concentrated and cleaned up on a silica gel solid-phase extraction column. Mebendazole was eluted from the column with 3% acetic acid in methanol. The eluate, after reconstitution in the chromatographic mobile phase, was analysed on a LiChrosorb RP-8 column with acetonitrile-0.05 M ammonium phosphate buffer (pH 6.2) (3:7, v/v) as the mobile phase. Detection was performed at 311 nm. The average mebendazole recovery over the concentration range 10-5000 micrograms/kg eel muscle tissue was 72 +/- 6.4%. The calibration curve for spiked samples was linear throughout the range 10-10,000 micrograms/kg (r = 0.999).

Comparative sulphoxidation of albendazole by sheep and cattle liver microsomes and the inhibitory effect of methimazole

1. The comparative rates of oxidation of the benzimidazole anthelmintic, albendazole (ABZ), by sheep and cattle liver microsomes, and inhibition by the antithyroid compound methimazole (MTZ) were investigated. 2. ABZ was oxidized to its sulphoxide metabolite (ABZSO) in an NADPH concentration-dependent reaction. Heat inactivation of the microsomal flavin-containing mono-oxygenase system significantly decreased the NADPH consumption of microsomes in the presence of ABZ, MTZ and thiourea. 3. Oxidation of ABZ, MTZ and thiourea by sheep liver microsomes consumed significantly more NADPH than oxidation by cattle microsomes. 4. Neither the pro-ABZ drug, netobimin, nor the ABZ sulphone metabolite (ABZSO2) was modified by incubation with either sheep or cattle liver microsomes. 5. ABZSO was oxidized into ABZSO2 at a very slow rate and only when a high microsomal protein concentration was used. 6. MTZ was a potent inhibitor of ABZ sulphoxidation and the inhibition was significantly lower in cattle than in sheep microsomes.

Plasma levels of mebendazole in children with hydatid disease

The plasma levels of mebendazole in children with hydatid cyst disease were measured with high pressure liquid chromatography. In 24 children who received mebendazole orally in a dose of 50 mg/kg, the mean (SD) level 4 hours later was 25.76(9.81) ng/ml (87.6(33) nanomole/l). This result was similar to those in most adult series. During more prolonged treatment, the plasma level 4 hours after the dose of the drug rose significantly with respect to the initial level (p < 0.05).

Application of a high-performance liquid chromatography coulometric method for the estimation of mebendazole and its metabolites in human sera

A novel, sensitive high-performance liquid chromatographic method, making use of coulometric detection, for the estimation of mebendazole and its metabolites in the sera of eight hydatidosis patients was devised. Recovery rates, precision, accuracy and sensitivity for each compound are reported and compared with those of the previously published methods.

Pharmacokinetic behaviour of netobimin and its metabolites in sheep

The pharmacokinetics and the profile of urine excretion of netobimin (NTB) and its metabolites were investigated after its intraruminal (i.r.) and subcutaneous (s.c.) administration to sheep at 20 mg/kg. Plasma and urine concentrations of NTB, albendazole (ABZ), albendazole sulphoxide (ABZSO) and albendazole sulphone (ABZSO2) were measured serially over a 120-h period by HPLC. NTB showed a similar pharmacokinetic profile in both treatments, being detected between 0.5 and 12 h post-treatment, but the tmax was achieved significantly earlier (P less than 0.05) after s.c. treatment. ABZ was detected in plasma only after i.r. treatment, resulting in a low area under the curve (AUC). The peak plasma concentration (Cmax) and AUC for ABZSO and ABZSO2 were significantly higher after i.r. administration of NTB. In both treatments, the ABZSO Cmax was reached earlier than the ABZSO2 Cmax. The ratio of AUC ABZSO2:ABZSO was higher following s.c. administration (1.33) than following i.r. administration (0.35). The percentages of total dose excreted in the urine as NTB, ABZ, ABZSO and ABZSO2 were 17.05 (i.r.) and 8.16 (s.c.). There was a less efficient conversion of NTB into ABZ metabolites after s.c. administration. The detection of ABZ in plasma and the high ABZSO AUC obtained after i.r. treatment may be of major importance for anthelmintic efficacy.

In vivo 31P NMR spectrum of Hymenolepis diminuta and its change on short-term exposure to mebendazole

The 31P NMR spectrum of the adult tapeworm, Hymenolepis diminuta, at 37 degrees C during perfusion with physiological saline was composed of 10 peaks. Based on chemical shifts and analysis of worm extracts, the phosphorus components included glucose-6-phosphate, fructose-6-phosphate, phosphorylcholine, glycerophosphoryl choline and -ethanolamine, nucleotide monophosphate-diphosphate and -triphosphate, nicotinamide adenine dinucleotide and uridine diphosphate glucose. The mean level of nucleotide triphosphate was 0.86 nmol (mg fresh weight)-1 and the nucleotide triphosphate/-diphosphate ratio 3.9. Based on the nucleotide triphosphate level, worms were viable for at least 3 h and the intracellular pH was maintained constant at approximately 6.7. Short-term exposure to mebendazole perfused at 11 or 27 microM solubilized in physiological saline containing 0.5% Tween 80 or 0.1% dimethyl sulphoxide had little effect on the nucleotide triphosphate level. Some cytological changes, however, were evident following perfusion of mebendazole. In contrast, exposure to 2,4-dinitrophenol caused a rapid decline in nucleotide triphosphate level. It was concluded that mebendazole does not exert its primary effect on oxidative phosphorylation.

Comparison of inhibition of polymerisation of mammalian tubulin and helminth ovicidal activity by benzimidazole carbamates

The correlation between the inhibition of hatching of Haemonchus contortus eggs and inhibition of mammalian tubulin polymerisation by benzimidazole carbamates has been investigated. The hatching process was observed to be independent of the biomass (eggs plus debris) over a 6-fold range and the early (E1-E3) stages of egg development, but was dependent on the concentration of co-solvent (DMSO) and time of incubation. Benzimidazole carbamates with strong inhibitory activity against mammalian tubulin were potent inhibitors of egg hatch, while non-inhibitors failed to prevent hatching. It is postulated that the primary mode of action of these drugs on nematode eggs is the inhibition of microtubule-dependent processes within the developing egg. The implications and limitations of this correlation are discussed.

Potentiation of the anthelmintic activity of oxfendazole by parbendazole

The ability of parbendazole (PBZ) to potentiate co-administered oxfendazole (OFZ) was investigated. Administration of a range (1.35-36.0 mg/kg) of doses of PBZ with 4.53 mg OFZ/kg demonstrated that significant potentiation occurred at 4.5 mg PBZ/kg. At 4.5 mg PBZ/kg, the area under the plasma OFZ concentration curve was about twice that obtained from oral administration of OFZ alone. When tested against benzimidazole-resistant Haemonchus contortus and Trichostrongylus colubriformis, the mixture of 4.5 mg PBZ + 4.53 mg OFZ/kg was significantly more effective than 4.53 mg OFZ/kg alone, and PBZ alone showed no activity against these resistant nematodes. The demonstration of PBZ-OFZ potentiation has indicated a means of obtaining a more effective use of currently available anthelmintics in the treatment of helminthiasis.

Drug level monitoring: chromatography of some minor groups of drugs

Some important facts about the chromatographic separation of a number of selected categories of drugs are summarized. The data refer to the chromatographic method of choice, stationary phase, mobile phase (carrier gas), detection procedure and (where available) method sensitivity. Also, fundamental instrumental parameters, namely injector, column and detector temperature, carrier gas and mobile phase flow-rate and gradient set-up are reported here. In all cases also the source material used for analysis is specified. The data are presented in table form, each table dealing with a particular category of drugs. The following categories of drugs are being dealt with: anthelmintics, antiarteriosclerotics, antibacterials, anticholinergics and cholinergics, anticoagulants, antidiabetics, antiemetics, antimycotics, antihistamines, antimalarials, antiparasitics, antiparkinsonics, antitussives, antiulcer drugs, antiviral compounds, appetite depressants and immunosuppressives.

The pharmacokinetics and bioavailability of a tracer dose of [3H]-mebendazole in man

Five volunteers, whose ages ranged between 37 and 64 years, took part in a crossover study to determine the pharmacokinetics and bioavailability of mebendazole in man following intravenous and oral administration of a tracer dose of [3H]-mebendazole. Following intravenous administration, the average distribution half-life, elimination half-life and rate of clearance were 0.20 h, 1.12 h, and 1.063 min respectively. After oral administration of the solution, the average elimination half-life was 0.93 h, the apparent rate of clearance was 0.846 l/min, the average time to peak plasma concentration was 0.42 h, and the bioavailability of mebendazole was 22%. Comparison of metabolite area under the plasma concentration vs time data from each route of administration indicates that absorption of mebendazole from the gastrointestinal tract at this dose level is almost complete. The low bioavailability observed following oral administration at this dose level is postulated to be due to high first pass elimination. Approximately half of the administered dose of radioactivity following intravenous and oral administration was detected in the urine, and the major unconjugated metabolite of mebendazole was found to be 2-amino-5(6) [alpha-hydroxybenzyl]benzimidazole (IV), not 2-amino-5(6)benzoylbenzimidazole (II), as previously reported.

Cyst and host tissue concentrations of mebendazole in patients undergoing surgery for hydatid disease

Mebendazole levels were assayed by high performance liquid chromatographic assay in plasma, host tissues, and hydatid material taken from four patients who underwent surgery for hydatid disease. The drug was absorbed and had penetrated both into the host and into the parasite material. The levels of the drug in viable hydatid cysts were much lower than those in dead cysts. The possibility of exclusion or detoxification of the drug by viable hydatid cysts is raised.

4-Amino-3-(3'-methoxycarbonyl-2'-thioureido)benzophenone, a prodrug of mebendazole

The compound 4-amino-3-(3'-methoxycarbonyl-2'-thioureido) benzophenone has shown promise as a prodrug of the anthelmintic mebendazole. The compound is stable in acid and neutral media and is rapidly hydrolysed in base. An HPLC assay procedure for mebendazole, the prodrug and their known or expected metabolites and degradation products in aqueous media and rat blood has been developed. The prodrug administrated orally to rats is rapidly converted to mebendazole. The area under the blood level versus time curve of mebendazole, in rats dosed with the prodrug, is more than twice that obtained after dosing rats with an equimolar amount of mebendazole. Only the prodrug, mebendazole and known metabolites of mebendazole are detected in rats dosed with the prodrug.

The metabolic and pharmacokinetic disposition of mebendazole in the rat

The metabolism and pharmacokinetics of mebendazole was studied in rats using [2'-3H]-mebendazole (biologically stable; specific activity 383.9 (mCi/mMol) and [2-14C]-mebendazole (specific activity 2.57 mCi/mMol). Analyses were performed by high pressure liquid chromatography and liquid scintillation spectrometry. About 85% of an intravenous dose was eliminated with the bile and the remainder with the urine. The majority of the dose was recovered as conjugated metabolites. The major metabolite (methyl-5(6)-(alpha-hydroxybenzyl)-2-benzimidazole carbamate) accounted for about 77% of the total recovered and 99% of it was conjugated. Anaerobic metabolism studies conducted in vitro with intestinal microorganisms obtained from rats indicated that metabolism of mebendazole did not occur in the gut, but that the intestinal microflora was able to hydrolyse conjugated metabolites which were eliminated with the bile. Mebendazole was found to have a biphasic elimination profile after intravenous administration. Its terminal plasma elimination half-life was 3.2 hours and its re-distribution half-life was 0.4 hour. After oral administration, as a solution in aqueous dimethyl sulphoxide, a bioavailability of 53% was obtained.

Sample preparation by salts precipitation and quantitation by high-performance liquid chromatography with UV detection of selected drugs in biological fluids

A quantitative clean-up procedure for drugs in plasma and urine in preparation for high-performance liquid chromatographic analysis is discussed. Samples are mixed with zinc sulfate, barium hydroxide, and acetonitrile (or methanol). Resultant solutions are clear and free of visible residue. Injections of over 420 samples of treated urine and 120 samples of treated plasma had no noticeable effect on pressure drop and column performance. An examination of the column head indicated no damage or discoloration to the packing. Baselines of the controls show no interference from endogenous compounds for the drugs studied. Precision study using cyclobenzeprine . HCl in plasma and urine by internal standard and external standard methods has within-run and day-to-day variations of under 5%. Drugs studied in urine and plasma are amiloride . HCl, cyclobenzeprine . HCl, cyproheptadine . HCl, diflunisal, indomethacin, phenylbutazone and sulindac. These drugs are selected for the various functional groups, their binding by proteins and their natural UV absorptivity. Conditions to improve recovery, advantages and limitations are discussed.

Preliminary observations on the biliary elimination of mebendazole and its metabolites in patients with echinococcosis

The biliary excretion of mebendazole has been investigated in two patients to whom it was given for the treatment of echinococcosis, although it was found to be only partly effective. Oral mebendazole was extensively metabolized and the conjugated parent substance and its metabolites were excreted in the bile. One patient without cholestasis and with normal liver function had an apparent total biliary clearance (776 ml/min) which approached the hepatic plasma flow. The other patient with cholestasis and impairment of the hepatic drug metabolizing capacity showed a drastically reduced apparent total biliary clearance of 3.8 ml/min. The average plasma level of mebendazole was significantly lower in the former and higher in the latter patient (0.06 and 0.91 nmol/ml, respectively). The data suggest that impaired metabolism and/or biliary elimination can account for the higher plasma mebendazole level in patients with liver damage.

Chemotherapy of larval echinococcosis with mebendazole: microsomal liver function and cholestasis as determinants of plasma drug level

High oral doses of mebendazole have been only partly effective in the treatment of patients with alveolar or cystic echinococcosis, possibly due to an inadequate plasma concentration of the drug in some patients. In order to improve therapeutic results the influence of liver function on the plasma levels of mebendazole was investigated during long term therapy. Plasma mebendazole concentrations measured before the morning dose (trough values) showed a highly significant, negative correlation both with the aminopyrine breath test (ABT; rs = -0.78, n = 14, p less than 0.001) and the second exponential component of bromsulphthalein elimination (BSP- k2; rs = -0.74, n = 12, p less than 0.01). These relationships also applied over longer than a single day, since trough and peak mebendazole levels observed over an interval of 6 months before and after testing liver function were equally well correlated with ABT and BSP-k2. The daily dosage and other liver function tests seemed to be of minor importance in determining the plasma levels. It was concluded that the microsomal function of the liver and/or cholestasis might be important determinants of plasma mebendazole levels. The results of the study imply that higher and more effective mebendazole concentrations might be achieved by inhibition of the drug metabolizing capacity of the liver rather than by increasing the dose of mebendazole.

Thin-layer chromatographic determination of indolic tryptophan metabolites in human urine using Sep-Pak C18 extraction

Tryptophan and some of its indole metabolites were separated by thin-layer chromatography, stained with the Van Urk--Salkowski reagent, and quantitated by scanning densitometry. The application of this technique for the detection of the indoles in urine samples, employing Sep-Pak C18 cartridges for extraction, was demonstrated. The proposed method is simple and accurate. The detection limits were 2 micrograms/ml 5-hydroxytryptophan, 1.75 micrograms/ml 5-hydroxyindolyl-3-acetic acid, 1.5 micrograms/ml tryptophan, 0.8 micrograms/ml indolyl-3-acetic acid, 0.9 micrograms/ml indolyl-3-butyric acid, 1.75 micrograms/ml serotonin, and 1.25 micrograms/ml tryptamine.

Identification of biliary metabolites of mebendazole in the rat

Three metabolites of mebendazole were isolated from the bile of rats dosed with a mixture of mebendazole and pentadeuteromebendazole. The identification was based upon the appearance of the characteristic doublet in the mass spectrum of the compounds and the comparison of their fragmentations with those of authentic compounds. Cochromatography of the metabolites with the authentic compounds on HPLC supported the identification. Methyl-5(6)-(alpha-hydroxybenzyl)-2-benzimidazole carbamate, 2-amino-5(6)-(alpha-hydroxybenzyl) benzimidazole and 2-amino-5(6)-benzoylbenzimidazole were identified as metabolites after enzymic conjugate hydrolysis. Some unmetabolized mebendazole was also found.

Chemotherapy for larval echinococcosis in animals and humans: report of a workshop

Mebendazole, its fluorine analogue flubendazole, and other benzimidazole derivatives are active against many gastrointestinal and tissue-stage helminths. This article reviews the published literature and proceedings of a workshop on the use of benzimidazoles against larval echinococcosis (hydatid disease). Orally administered high doses (30-50 mg/kg body weight) of mebendazole given daily for 20-90 days to rodents or sheep infected with larval Echinococcus granulosus cause damage of destruction of the cyst wall, loss of cyst fluid, and death of protoscolices. Similar treatment of rodents infected with E. multilocularis with mebendazole, flubendazole, fenbendazole, and albendazole for 60-300 days leads to reduction of weight, inhibition of growth and the metastases formation of E. multilocularis tissue, and to prolonged host survival time although the metacestodes are not killed. Mebendazole or flubendazole treatment of human patients infected with E. granulosus is followed by subjective improvement in most, and evidence of regression of cysts in some; in other patients, cysts continue to grow or have been proven viable even after several months of high-dose mebendazole therapy. In patients infected with E. Multilocularis, the progressive course of the disease appeared to be arrested, but treatment apparently did not kill the parasite. Side effects of some patients have included allergic reactions, alopecia, and reversible neutropenia. Some possible reasons for different responses to treatment include inadequate plasma drug absorption from the gut and age, condition, and location of cysts. Many remaining questions concerning the risk versus benefits of mebendazole therapy can be answered only through controlled clinical trials.

Clinical pharmacokinetics of high dose mebendazole in patients treated for cystic hydatid disease

The plasma concentrations of mebendazole and its metabolites have been monitored in twelve patients after receiving a 10 mg/kg dose for cystic hydatid disease. The mebendazole plasma concentration-time profiles differed considerably between patients; elimination half-lives ranged from 2.8-9.0 h, time to peak plasma concentration after dosing ranged from 1.5-7.25 h and peak plasma concentrations ranged from 17.5 to 500 ng/ml. The mean peak plasma concentration of mebendazole after an initial dose (69.5 ng/ml) was lower than found in patients during chronic therapy (137.4 ng/ml). The plasma AUCTS for the major metabolites of mebendazole (methyl 5-(alpha-hydroxybenzyl)-2-benzimidazole carbamate and 2-amino-5 benzoylbenzimidazole) were about five times the plasma AUCT found for mebendazole in patients on chronic therapy. It is suggested that the slower clearance of these polar metabolites relative to mebendazole results from enterohepatic recycling. Since mebendazole is also highly plasma protein bound, caution should be observed in administering mebendazole to patients with liver disease. Concentrations of mebendazole found in the tissue and cyst material collected from two patients during surgery ranged from 59.5 to 206.6 ng/g wet weight.