Determination of nitroimidazole residues in porcine urine by liquid chromatography/tandem mass spectrometry

A reliable and sensitive method was developed for determination of nitroimidazoles in porcine urine. Sample preparation involves an extraction with ethyl acetate, followed by a solid-phase extraction cleanup step. The final extract is injected into the liquid chromatography/tandem mass spectrometry system in the positive-ion electrospray ionization mode. A C8 column with water and acetonitrile as the mobile phase is used for chromatographic separation under gradient conditions. Overall average recoveries ranged from 83 to 107%. The limits of detection ranged from 0.03 to 0.05 ng/mL, and the limits of quantitation, from 0.1 to 0.2 ng/mL.

A rapid and simple assay to determine the blood and urine concentrations of 1-(5-[123/125I]iodo-5-deoxyarabinofuranosyl)-2-nitroimidazole, a hypoxic cell marker

Pharmacokinetic and dosimetric parameters of the hypoxic tissue imaging agent iodoazomycin arabinoside (123I-IAZA) have been investigated in human volunteers. In conjunction with this study it was necessary to develop an assay for low levels of the radiolabelled compound in blood and urine. A combination of high-performance liquid chromatography (HPLC) and gamma counting produced a highly selective, sensitive and rapid assay for the analysis of 123/125I-IAZA in human and animal blood and urine samples. Conventional HPLC assays for the tracer quantities of this radioactive agent in blood have not been reported previously. The addition of non-radiolabelled IAZA to the blood and urine samples containing radiolabelled IAZA allowed the pharmaceutical to serve as its own internal standard. This reverse isotope dilution approach permitted identification of the appropriate HPLC peak by UV detection, followed by highly sensitive quantification of the radiolabelled species by gamma counting. Blood samples were prepared for HPLC by a solid-phase extraction without the loss of IAZA from serum, with an extraction efficiency of 99.7 +/- 7.1% from human serum. Urine samples could be analyzed directly by HPLC, without the solid-phase extraction step. The detection limit in biological fluids depends on the specific activity of radiolabelled 123/125I-IAZA. In this study it was possible to detect serum concentrations of 123I-IAZA as low as 7.46 pg (21 fmol) per ml. The radiometric detection limit for 123I-IAZA in this assay was 10.8 Bq ml-1 of serum.

The pharmacokinetics, bioavailability and biodistribution in mice of a rationally designed 2-nitroimidazole hypoxia probe SR-4554

N-(2-Hydroxy-3,3,3-trifluoropropyl)-2-(2-nitro-1-imidazolyl) acetamide (SR-4554) is a fluorinated 2-nitroimidazole which has been rationally designed as a non-invasive probe for tumor hypoxia. The key selection criteria for this molecule were low central nervous system penetration and toxicity, high metabolic stability other than nitroreduction, good tumor uptake and high sensitivity for detection by magnetic resonance spectroscopy. As part of the pre-clinical development strategy, pharmacokinetic, bioavailability and biodistribution studies were performed in mice. Pharmacokinetic studies in mice demonstrated that SR-4554 was rapidly absorbed into plasma following i.p. administration and eliminated with a half-life of 42 min, similar to other 2-nitroimidazoles. By comparing the areas under the concentration-time curve (AUC), the tumor exposure towards SR-4554 was on average 84% of the value obtained for the plasma exposure. SR-4554 penetrated tumor tissue extremely well but, in contrast to misonidazole and certain other fluorinated analogues, its distribution into brain tissue was poor (AUCbrain/AUCplasma = 0.07), suggesting potentially lower toxicity in spite of its higher lipophilicity (P = 0.43 versus 0.63, respectively). The bioavailability of SR-4554 from i.p. and p.o. routes was 100 and 96% respectively. In non-tumor-bearing mice, SR-4554 was excreted mainly as unchanged drug. The percentage of the injected i.p. dose of SR-4554 excreted unchanged in the urine over 24 h was 68 +/- 8%. Neither SR-4554 nor its metabolites were detected in mouse feces. We propose that these favorable pharmacokinetic properties of SR-4554 are due to the hydrophilic character and hydrogen-bonding capability of the amide and hydroxyl functions in the compound.

Lack of stereoselectivity in the pharmacokinetics and metabolism of the radiosensitizer Ro 03-8799 in man

During a clinical toxicity study it was possible to obtain urine samples from six patients receiving either the R-(-)- or S-(+)-stereoenantiomeric forms of the developmental 2-nitroimidazole radiosensitizer Ro 03-8799 (pimonidazole). Paired plasma samples were also obtained from four patients. The pharmacokinetic data were compared with those for the racemic mixture in the same individuals. The results revealed no major differences in the plasma pharmacokinetics, urinary clearance or N-oxidation of the individual enantiomers as compared with the racemic mixture. A similar lack of stereoselectivity with respect to the acute dose-limiting CNS toxicity syndrome suggests that this may not involve a specific CNS receptor interaction.

Pharmacokinetics of etanidazole (SR-2508) in bladder and cervical cancer: evidence of diffusion from urine

Following an IV infusion of 2.0 g/m2 of Etanidazole, the mean tumor concentration 40 min after injection was 126 micrograms/g in bladder cancer and 65 micrograms/g in cervical cancer. The tumor/plasma concentration ratio was 1.88 in bladder and 0.85 in cervical cancer. This high tumor concentration in bladder cancer could be accounted for by diffusion from a highly concentrated urine. This renders bladder cancer a suitable clinical model for testing this sensitizer.

Relationship between lipophilic character and urinary excretion of nitroimidazoles and nitrothiazoles in rats

Many processes are involved in the renal excretion of drugs, but very little is known about their quantitative structure-activity relationship. The relationship between urinary excretion and lipophilic character of a series of nitroimidazoles and nitrothiazoles was studied. The unmetabolized forms of the drugs were detected in the urine by means of UV and HPLC procedures. The urinary excretion of unmetabolized forms is parabolically related with the log P, as an expression of lipophilic character of molecules.

Urinary metabolites of the antiprotozoal agent cis-3a,4,5,6,7,7a- hexahydro-3-(1-methyl-5-nitro-1H-imidazol-2-yl)-1,2-benzisoxazole in the rat

1H-NMR and MS were employed to identify 13 rat urinary metabolites of 14C-labeled cis-3a,4,5,6,7,7a- hexahydro-3-(1-methyl-5-nitro-1H-imidazol-2-yl)-1,2-benzisoxazole (MK-0436). The major free (unconjugated) metabolite was cis-3a,4,5,6,7, 7a-hexahydro-3-carboxamido-1,2-benzisoxazole; it was also the second most abundant metabolite released during hydrolysis of the conjugated fraction. All other identified metabolites were hydroxylated analogues substituted at C(4)-C(7a) of the cyclohexane ring. the 4-equatorial,5-axial,7a-triol was the second most abundant metabolite excreted in an unconjugated form. Four monohydroxy (5-axial, 6-axial, 6-equatorial, 7-equatorial) metabolites of the drug were identified; they were found in the conjugated fraction only and were released by hydrolysis. The 5-axial hydroxy compound is the major conjugated metabolite and is overall the most abundant of all the metabolites. Six dihydroxy metabolites were identified: one was found exclusively in the free state, three as conjugates only (including the 7-axial,7a-diol, which is the major dihydroxy species), and two both free and conjugated. A second triol was found both free and conjugated.

Detection of a reactive metabolite of misonidazole in human urine

Chemical studies have indicated that, following reduction of misonidazole to the hydroxylamine derivative, reaction with guanosine leads to the formation of a 2-carbon addition product of guanosine. In this study, the formation of the guanosine product is used to detect the presence of a reactive metabolite of misonidazole in the urine of patients treated with misonidazole. Urine samples were incubated with [14C]guanosine and the guanosine product was separated by HPLC analysis. The quantities of product vary as much as 10-fold from patient to patient and it is suggested that the assay might be useful as a predictor of patients susceptible to the development of peripheral neuropathy or other effects of misonidazole.

Identification of canine urinary metabolites of the antiprotozoal agent 3a,4,5,6,7,7a-hexahydro-3-(1-methyl-5-nitro-1H-imidazol-2-yl)-1,2-benzisoxazole

Metabolite fractions from the urine of a dog dosed with 3a,4,5,6,7a-hexahydro-3-(1-methyl-5-nitro-1H-imidazol-2-yl)-1,2-benzisoxazole (MK-0436) were obtained by the use of high-performance liquid chromatography. These fractions were of suitable purity for structural elucidation. Data obtained by mass spectrometry and NMR spectroscopy allowed the identification of seven major metabolites of this drug. Biotransformation in each case involved hydroxylation (mono or di) of the hexahydrobenzisoxazole ring.

High-performance liquid chromatographic determination of the nitroimidazole azanidazole in human plasma and urine

Azanidazole can be measured in plasma and urine by reversed-phase high-performance liquid chromatography employing UV detection. Peak mean plasma concentrations of azanidazole, of 267 ng/ml, occurred at 1.5 h after single oral doses to human subjects, and declined with a half-life of 0.8 h. Less than 0.5% of the dose was excreted in the urine as unchanged drug. Metabolites of azanidazole were also detected by the procedures used.

Urinary metabolites of 3a,4,5,6,7,7a-hexahydro-3-(1-methyl-5-nitro-1H-imidazol-2-yl)-1,2-benzisoxazole in the dog

The antiprotozoal drug 3a,4,5,6,7,7a-hexahydro-3-(1-methyl-5-nitro-1H-imidazol-2-yl)-1,2-benzisoxazole (I), which exhibits activity against trypanosomiasis, is also antibacterial in vivo. Since the urine from a dog dosed with I showed a broader spectrum of antibacterial activity than I itself, metabolites from this urine were isolated and partially characterized. The metabolites were mono- and dihydroxy-substituted species with the hydroxyl groups on carbons 4--7 of the hexahydrobenzisoxazole ring. These observations led to the synthesis of several such hydroxy derivatives of I, and their properties fully supported the proposed positions of metabolic hydroxylation. One synthetic compound, the 6,7-cis-dihydroxy compound, exhibited higher antibacterial activity against Salmonella schottmuelleri in mice and greater trypanocidal activity in vivo against Trypanosoma cruzi (Brazil strain) than I.

Metabolism of 5-isopropyl-1-methyl-2-nitro-1H-imidazole. Identification of some urinary metabolites in the dog

The metabolism of 5-isopropyl-1-methyl-2-nitro-1H-[2-14C] imidazole in dogs has been investigated after oral administration of 50 mg/kg. Three main metabolites, still containing the nitro group and accounting for about 50% of the total radiocarbon, together with a small amount of the unchanged drug, were isolated from the urine within 48 hr. The structures were determined by mass, infrared, and nuclear magnetic resonance spectroscopy. The biotransformations giving rise to the metabolites isolated involve the isopropyl chain of the molecule, either at the tertiary carbon atom or at one of the two methyl groups, or both. Thus, the metabolic behavior of this 2-nitroimidazole derivative appears to be similar to that previously demonstrated for the class of the isomeric 5-nitroimidazoles.

Determination of nitroimidazoles in biological fluids by differential pulse polarography

A sensitive differential pulse polarographic assay was developed for the determination of metronidazole, ornidazole, and 2-nitro-1H-imidazole-1-(3-methoxy-2-propanol) in plasma. The compounds are selectively extracted into ethyl acetate from a protein-free filtrate of plasma, buffered to pH 7.0 +/- 0.2. The residue of the ethyl acetate extract is dissolved in 0.1 N NaOH and analyzed by differential pulse polarography for the reduction of the nitro group at approximately -0.600 v versus the saturated calomel electrode. The overall recovery from plasma was about 55 +/- 3.0% (SD) for the three compounds investigated. A TLC step after the ethyl acetate extraction may also be included to ensure specificity. This step reduced the overall recovery to approximately 45%. The sensitivity limit of detection from plasma using a 2-ml sample is 0.1 mug/ml. The assay may also be employed for the analysis of urine. The urine is adjusted to pH 7.0 +/- 0.2 and extracted with ethyl acetate, and the residue is analyzed as described for plasma. The assay was applied to the determination of ornidazole in blood and urine in the dog following 10 mg/kg po.

Comparative pharmacokinetic studies of ornidazole and metronidazole in man

Pharmacokinetic characteristics of ornidazole and metronidazole were compared in man. Both drugs were labelled with 14C in the imidazole ring at position 2. Four healthy volunteers were given an oral dose of 750 mg of one of the drugs, followed 2--4 weeks later by the same dose of the other. The same technique for determining the unchanged compound was used for both drugs. Results may be summarized as follows: mean peak concentrations in the plasma of 10.9 mug/ml for ornidazole and of 12.3 mug/ml for metronidazole were reached 2--4 h and 30--60 min after administration, respectively; both drugs showed the same volume of distribution. Their binding to human plasma proteins was less than 15%; the mean half-life of elimination from the plasma was 14.4 h for ornidazole and 8.4 h for metronidazole; the mean radioactivity recovered from the urine and faeces during the first 5 days was 85% of the dose for ornidazole and 91% for metronidazole, the major proportion in each case being excreted in the urine; the radioactivity found in the faeces was 22.1% of the dose for ornidazole and 13.9% for metronidazole.