Rapid and selective high-performance liquid chromatographic method for the determination of metronidazole and its active metabolite in human plasma, saliva and gastric juice

Rapid Determination of Metronidazole and 2-Hydroxymetronidazole in Murine Blood Plasma

Metronidazole is a drug used to treat bacterial and protozoan infections. Nowadays, it is one of the most frequently prescribed drugs worldwide. The main aim of this paper is to present a rapid, reliable and simple high-performance liquid chromatography (HPLC) method to determine metronidazole along with its primary metabolite, 2-hydroxymetronidazole, in plasma or serum using paracetamol as an internal standard. A total of 100% methanol was used to denature plasma proteins. After centrifugation, the supernatant was evaporated under nitrogen flow. The samples were dissolved in the mobile phase and injected into a Li-Chrospher RP-18 column. A total of 10 mmol/L NaH2PO4: acetonitrile (90:10, v/v) solution with a flow rate of 1 mL/min was used as the mobile phase. Metronidazole and 2-hydroxymetronidazole were detected at two different wavelengths at 320 nm and 311 nm, respectively. The method is characterized by high precision (relative standard deviation % < 6). The method was used for the determination of metronidazole and 2-hydroxymetronidazole in murine blood using small amounts of plasma (≤100 μL).

Development and validation of a liquid chromatography tandem mass spectrometry assay for the measurement of faecal metronidazole

BACKGROUND

Metronidazole is an oral antibiotic which is widely used in the treatment of patients with Clostridium difficile associated disease.

METHODS

This article describes the validation of a LC-MS/MS assay for the measurement of metronidazole in human faecal samples.

RESULTS

Matrix matched and aqueous standards showed no significant difference in performance for the routine calibration of the assay. D⁴ deuterated metronidazole internal standard eluted with a different retention time to the undeuterated metronidazole on chromatography, hence zidovudine was used as an internal standard. Ion suppression was noted for both metronidazole and zidovudine due to unidentified compounds present in the faecal matrix and this was improved by extracting a smaller quantity of faeces and diluting the extract prior to analysis. Measurement uncertainty was 13% at 28,400ng/ml, 7.2% at 3300ng/ml, 3.9% at 320ng/ml, 13.6% at 109ng/ml and 30.9% at 20ng/ml. The assay was shown to be linear on dilution and the sensitivity of the assay was superior to HPLC assays using UV detection. The limit of detection was 5ng/ml, the limit of quantitation was 66ng/ml and the upper limit of the working range was 30,000ng/ml. Patient samples were stable at -20°C for 12months and extracted faecal samples were stable on storage for 1week at 4°C. There were no specific requirements for patient preparation or time of sample collection relative to taking metronidazole.

CONCLUSIONS

Metronidazole can be quantified in faecal samples using LC-MS/MS which opens up opportunities for further research in this area.

Concentrations of metronidazole in human plasma and saliva after tablet or gel administration

OBJECTIVES

The aim of this study was to determine the pharmacokinetic profile of metronidazole (Mtz) tablet and to compare Mtz gel and tablet concentrations in both blood plasma and saliva.

METHODS

In this randomized cross-over study with a 1-week washout period, 13 volunteers randomly received one (a single oral dose of 750 mg Mtz (Flagyl®--tablet) and 2) 3 g of 15% Mtz benzoate gel (applied by using a dental tray). The HPLC with ultraviolet detection was used to quantify plasma and saliva concentrations of Mtz. The pharmacokinetic parameters (PPs) areas under the curves from 0 to 48 h (AUC0-48) and from 0 to infinity (AUC0-∞), the maximum plasma concentration (C(max)), the time to C(max), volume of distribution and renal clearance were determined for Mtz tablet.

KEY FINDINGS

Considering the Mtz tablet, plasma showed higher Mtz concentration from 6 to 24 h after drug administration and the highest values concerning AUC0-48 h and AUC0-∞ than those obtained in saliva (P < 0.05). No significant differences were observed between plasma and saliva concentrations for Mtz gel.

CONCLUSIONS

The study showed that some PPs were higher in plasma (P < 0.05) than in saliva concerning Mtz tablet. Gel formulation had similar Mtz bioavailability in plasma and saliva resulting in systemic absorption.

Levofloxacin plus metronidazole administered once daily versus moxifloxacin monotherapy against a mixed infection of Escherichia coli and Bacteroides fragilis in an in vitro pharmacodynamic model

Moxifloxacin has been suggested as an option for monotherapy of intra-abdominal infections. Recent data support the use of a once-daily metronidazole regimen. The purpose of this study was to investigate the activity of levofloxacin (750 mg every 24 h [q24h]) plus metronidazole (1,500 mg q24h) compared with that of moxifloxacin (400 mg q24h) monotherapy in a mixed-infection model. By using an in vitro pharmacodynamic model in duplicate, Escherichia coli and Bacteroides fragilis were exposed to peak concentrations of 8.5 mg of levofloxacin/liter q24h, 32 mg of metronidazole/liter q24h, and 2 mg for moxifloxacin/liter q24h for 24 h. The activities of levofloxacin, metronidazole, moxifloxacin, and levofloxacin plus metronidazole were evaluated against E. coli, B. fragilis, and E. coli plus B. fragilis. The targeted half-lives of levofloxacin, metronidazole, and moxifloxacin were 8, 8, and 12 h, respectively. Time-kill curves were analyzed for time to 3-log killing, slope, and regrowth. Pre- and postexposure MICs were determined. The preexposure levofloxacin, metronidazole, and moxifloxacin MICs for E. coli and B. fragilis were 0.5 and 1, >64 and 0.5, and 1 and 0.25 mg/liter, respectively. Levofloxacin and moxifloxacin achieved a 3-log killing against E. coli and B. fragilis in all experiments, as did metronidazole against B. fragilis. Metronidazole did not decrease the starting inoculum of E. coli. The area under the concentration-time curve/MIC ratios for E. coli and B. fragilis were 171.7 and 85.9, respectively, for levofloxacin and 26 and 103.9, respectively, for moxifloxacin. Levofloxacin plus metronidazole exhibited the fastest rates of killing. The levofloxacin and moxifloxacin MICs for B. fragilis increased 8- to 16-fold after the organism was exposed to moxifloxacin. No other changes in the postexposure MICs were found. Levofloxacin plus metronidazole administered once daily exhibited activity similar to that of moxifloxacin against the mixed E. coli and B. fragilis infection. A once-daily regimen of levofloxacin plus metronidazole looks promising for the treatment of intra-abdominal infections.

Pharmacodynamics of pulse dosing versus standard dosing: in vitro metronidazole activity against Bacteroides fragilis and Bacteroides thetaiotaomicron

Pulse dosing is a novel approach to dosing that produces escalating antibiotic levels early in the dosing interval followed by a prolonged dose-free period. Antibiotic is frontloaded by means of four sequential bolus injections, after which antibiotic levels are allowed to diminish until the next dose. This study compares standard thrice-daily dosing and pulse dosing of metronidazole against Bacteroides spp. in an in vitro model. Two American Type Culture Collection Bacteroides fragilis isolates (metronidazole MIC for each organism = 1 mg/liter) were exposed to metronidazole for 48 or 96 h. Human pharmacokinetics were simulated for an oral 500-mg dose given every 8 h (maximum concentration of drug [C(max)] = 12 mg/liter; half-life = 8 h; area under the curve [AUC] = 294 mg . h/liter) and for pulse dosing. Pulses, each producing an increase in metronidazole concentration of 9 mg/liter, were administered at times 0, 2, 4, and 6 h of each 24-h cycle, with a targeted half-life of 8 h (AUC = 347 mg . h/liter). A metronidazole-resistant B. fragilis strain (metronidazole MIC = 32 mg/liter) was exposed to both dosing regimens and, additionally, to a regimen of 1,500 mg administered once daily (C(max) = 36 mg/liter; AUC = 364 mg . h/liter). Furthermore, regimens against one B. fragilis isolate and one B. thetaiotaomicron isolate corresponding to one-fourth and one-eighth of the thrice-daily and pulse dosing regimens, mimicking peak metronidazole concentrations achieved in abscesses, were simulated in 48-h experiments (metronidazole MIC = 1 mg/liter). Time-kill curves were generated for each experiment and analyzed for bactericidal activity, defined as a bacterial burden reduction >/= 3 log(10) CFU/ml. The results of paired (Wilcoxon matched-pair signed-rank test) and nonpaired (Mann-Whitney test) statistical analyses conducted on time to 3 log(10) kill data and area under the kill curve data from each of the thrice-daily dosing experiments versus each of the pulse dosing experiments were considered not significant for a given isolate-dosing regimen combination. The thrice-daily dosing, pulse dosing, and once-daily dosing regimens all exhibited bactericidal activity. Metronidazole administered in standard or pulse dosing fashion was highly active against both susceptible and resistant strains of Bacteroides spp.

Quantification of metronidazole in small-volume biological samples using narrow-bore high-performance liquid chromatography

A rapid, selective and sensitive HPLC assay has been developed for the routine analysis of metronidazole in small volumes of rat plasma, gastric aspirate and gastric tissue. The extraction procedure involves liquid-liquid extraction and a protein precipitation step. A microbore Hypersil ODS 3 microm (150 x 2.1 mm I.D.) column was used with a mobile phase consisting of acetonitrile-aqueous 0.05 M potassium phosphate buffer (pH 7) containing 0.1% triethylamine (10:90). The column temperature was at 25 degrees C and the detection was by UV absorbance at 317 nm. The limit of detection was 0.015 microg ml(-1) for gastric juice aspirate and plasma and 0.010 microg g(-1) for gastric tissue (equivalent to 0.75 ng on-column). The method was linear up to a concentration of 200 microg ml(-1) for plasma and gastric juice aspirate and up to 40 microg g(-1) for tissue, with inter- and intra-day relative standard deviations less than 14%. The measured recovery was at least 78% in all sample matrices. The method proved robust and reliable when applied to the measurement of metronidazole in rat plasma, gastric juice aspirate and gastric tissue for pharmacokinetic studies in individual rats.

Influence of age on the steady state disposition of drugs commonly used for the eradication of Helicobacter pylori

BACKGROUND

The success of eradication therapy for Helicobacter pylori might be affected by the age of patients.

AIM

To investigate whether disposition of drugs commonly used for H. pylori eradication is age-dependent.

METHODS

Trough steady state serum levels of lansoprazole or ranitidine, amoxycillin, clarithromycin and metronidazole were monitored in 232 patients during the last dosing interval of a 5-day quadruple H. pylori eradication regimen. Detailed pharmacokinetic analysis was performed in 28 patients.

RESULTS

Linear correlations between age and trough serum levels were observed with lansoprazole (r=0.25; P=0.002), ranitidine (r=0. 38; P=0.001) and clarithromycin (r=0.36; P < 0.0001). These associations were also inversely dependent of creatinine clearance for ranitidine (r=0.36; P=0.001) and clarithromycin (r=0.30; P < 0. 0001). Multiple linear regression revealed age as an important factor influencing trough serum levels of lansoprazole, clarithromycin and ranitidine. There were significant inverse relationships between creatinine clearance and area under curve of ranitidine (r=0.88; P < 0.0001) and amoxycillin (r=0.56; P=0.002). Multiple linear regression revealed serum creatinine as the most important factor influencing the area under curve of ranitidine, clarithromycin and amoxycillin.

CONCLUSIONS

Age per se has little influence on pharmacokinetics of amoxycillin and ranitidine, which depend more on age-dependent decline in renal function. The influence of age, but not renal function was established for lansoprazole. Age and renal function have independent impacts on clarithromycin disposition.

In vitro assessment of gastric mucosal transfer of anti-Helicobacter therapeutic agents

A novel animal model for studying antibiotic transfer across gastric mucosa was developed by using adult rats. Gastric corpus mucosa was mounted in an Ussing chamber system and bathed in oxygenated Krebs solution. Metronidazole flux from serosa to mucosa (J(S-->M)) was measured over 60 min under basal conditions and compared with mucosa-to-serosa flux (J(M-->S)). The effects of varying the chamber cross-sectional diameter and of stimulation by histamine and carbachol were assessed. Metronidazole J(M-->S) was measured with the mucosal pH at 2.2, 2.7, 3.2, and 7.4. Amoxicillin J(S-->M) under basal conditions was also measured and compared with metronidazole J(S-->M). Metronidazole J(S-->M) was proportional to serosal concentration (P < 0.001) under basal conditions, being 3.98 nmol x h(-1) x cm(-2) with a serosal concentration of 0.2 mmol/liter. Amoxicillin J(S-->M) was significantly lower under similar conditions at 0.50 nmol x h(-1) x cm(-2) (P < 0.01). Metronidazole J(S-->M) was not significantly different from J(M-->S), between chambers of different sizes, or following stimulation. When the mucosal pH was changed, J(M-->S) was proportional to the un-ionized concentration on the mucosal side (P < 0.001). Therefore, this model shows properties analogous to those of human gastric mucosa in vivo, with partitioning of metronidazole on the mucosal side according to pH, diffusion of metronidazole across the mucosa in both directions, and selectivity for different antibiotics, and it will be useful for the study of other therapeutic agents in the treatment of Helicobacter pylori.