Liquid chromatographic assay for metronidazole and tinidazole: pharmacokinetic and metabolic studies in human subjects

Hepatotoxicity of metronidazole in Cockayne syndrome: A clinical report

Cockayne syndrome (CS) is a rare autosomal recessive genetic disorder characterized by growth failure and progressive multisystem dysfunction caused by deficient nucleotide excision repair. Whereas metronidazole (MTZ) hepatotoxicity is quite rare in the general population, cases of severe hepatic reaction to MTZ have been reported in CS patients. We report here the case of a 21-year-old CS patient who presented with jaundice following one week of treatment with MTZ combined with spiramycin for dental care. This case is the first one documented with a liver biopsy. Histopathological analysis revealed portal and lobular inflammation with predominance of neutrophils, ballooning degeneration and severe cholestasis without bile duct damage. The outcome was marked by regression of jaundice over 6 weeks. Analysis of this case highlights the probable responsibility of MTZ and adds support to the recommendation to strictly avoid the prescription of this drug in CS patients.

Metronidazole: an update on metabolism, structure-cytotoxicity and resistance mechanisms

Metronidazole, a nitroimidazole, remains a front-line choice for treatment of infections related to inflammatory disorders of the gastrointestinal tract including colitis linked to Clostridium difficile. Despite >60 years of research, the metabolism of metronidazole and associated cytotoxicity is not definitively characterized. Nitroimidazoles are prodrugs that are reductively activated (the nitro group is reduced) under low oxygen tension, leading to imidazole fragmentation and cytotoxicity. It remains unclear if nitroimidazole reduction (activation) contributes to the cytotoxicity profile, or whether subsequent fragmentation of the imidazole ring and formed metabolites alone mediate cytotoxicity. A molecular mechanism underpinning high level (>256 mg/L) bacterial resistance to metronidazole also remains elusive. Considering the widespread use of metronidazole and other nitroimidazoles, this review was undertaken to emphasize the structure-cytotoxicity profile of the numerous metabolites of metronidazole in human and murine models and to examine conflicting reports regarding metabolite-DNA interactions. An alternative hypothesis, that DNA synthesis and repair of existing DNA is indirectly inhibited by metronidazole is proposed. Prokaryotic metabolism of metronidazole is detailed to discuss new resistance mechanisms. Additionally, the review contextualizes the history and current use of metronidazole, rates of metronidazole resistance including metronidazole MDR as well as the biosynthesis of azomycin, the natural precursor of metronidazole. Changes in the gastrointestinal microbiome and the host after metronidazole administration are also reviewed. Finally, novel nitroimidazoles and new antibiotic strategies are discussed.

Electrochemical Behaviour of Tinidazole at 1,4-Benzoquinone Modified Carbon Paste Electrode and Its Direct Determination in Pharmaceutical Tablets and Urine by Differential Pulse Voltammetry

A simple and highly sensitive electrochemical method based on a 1,4-benzoquinone modified carbon paste electrode (1,4-BQMCPE) was described for the determination of tinidazole (TDZ). In Britton Robinson buffer solution, TDZ yields well-defined irreversible reduction peak at -0.344 V on a 1,4-BQMCPE. Compared with that on a bare CPE, the reduction peak of TDZ increased significantly on the modified CPE and the effects of different parameters on the voltammetric responses were also investigated. Differential pulse voltammetric method was proposed and optimized for TDZ determination and its reductive peak current response at 1,4-BQMCPE was found to show linear dependence on the concentration of TDZ in the range of 1.0 × 10^-6 to 5.0 × 10^-4 M with a linear regression equation, correlation coefficient, limit of detection (LOD), and limit of quantification (LOQ) of I_PC (μA) = 0.19958 + 0.02657C (μM), 0.99486, 1.10 × 10^-7 M, and 3.77 × 10^-7, respectively. Excellent recovery results for spiked TDZ in pharmaceutical tablet samples ranging within 97.44-97.51% and in urine ranging within 95.37-96.91% were observed. The selectivity of the method for TDZ was further studied in the presence of selected potential interferents and confirmed the potential applicability of the developed method for the determination of TDZ.

The role of human cytochrome P450 enzymes in the formation of 2-hydroxymetronidazole: CYP2A6 is the high affinity (low Km) catalyst

Despite metronidazole's widespread clinical use since the 1960s, the specific enzymes involved in its biotransformation have not been previously identified. Hence, in vitro studies were conducted to identify and characterize the cytochrome P450 enzymes involved in the formation of the major metabolite, 2-hydroxymetronidazole. Formation of 2-hydroxymetronidazole in human liver microsomes was consistent with biphasic, Michaelis-Menten kinetics. Although several cDNA-expressed P450 enzymes catalyzed 2-hydroxymetronidazole formation at a supratherapeutic concentration of metronidazole (2000 μM), at a "therapeutic concentration" of 100 μM only CYPs 2A6, 3A4, 3A5, and 3A7 catalyzed metronidazole 2-hydroxylation at rates substantially greater than control vector, and CYP2A6 catalyzed 2-hydroxymetronidazole formation at rates 6-fold higher than the next most active enzyme. Kinetic studies with these recombinant enzymes revealed that CYP2A6 has a Km = 289 μM which is comparable to the Km for the high-affinity (low-Km) enzyme in human liver microsomes, whereas the Km values for the CYP3A enzymes corresponded with the low-affinity (high-Km) component. The sample-to-sample variation in 2-hydroxymetronidazole formation correlated significantly with CYP2A6 activity (r ≥ 0.970, P < 0.001) at substrate concentrations of 100 and 300 μM. Selective chemical inhibitors of CYP2A6 inhibited metronidazole 2-hydroxylation in a concentration-dependent manner and inhibitory antibodies against CYP2A6 virtually eliminated metronidazole 2-hydroxylation (>99%). Chemical and antibody inhibitors of other P450 enzymes had little or no effect on metronidazole 2-hydroxylation. These results suggest that CYP2A6 is the primary catalyst responsible for the 2-hydroxylation of metronidazole, a reaction that may function as a marker of CYP2A6 activity both in vitro and in vivo.

Systemic antibiotic therapy for chronic osteomyelitis in adults

The standard recommendation for treating chronic osteomyelitis is 6 weeks of parenteral antibiotic therapy. However, oral antibiotics are available that achieve adequate levels in bone, and there are now more published studies of oral than parenteral antibiotic therapy for patients with chronic osteomyelitis. Oral and parenteral therapies achieve similar cure rates; however, oral therapy avoids risks associated with intravenous catheters and is generally less expensive, making it a reasonable choice for osteomyelitis caused by susceptible organisms. Addition of adjunctive rifampin to other antibiotics may improve cure rates. The optimal duration of therapy for chronic osteomyelitis remains uncertain. There is no evidence that antibiotic therapy for >4-6 weeks improves outcomes compared with shorter regimens. In view of concerns about encouraging antibiotic resistance to unnecessarily prolonged treatment, defining the optimal route and duration of antibiotic therapy and the role of surgical debridement in treating chronic osteomyelitis are important, unmet needs.

Method validation and determinations of levofloxacin, metronidazole and sulfamethoxazole in an aqueous pharmaceutical, urine and blood plasma samples using quantitative nuclear magnetic resonance spectrometry

Selective, rapid and accurate quantitative proton nuclear magnetic resonance (qHNMR) method for the determination of levofloxacin, metronidazole benzoate and sulfamethoxazole in aqueous solutions was developed and validated. The method was successfully applied to the determinations of the drugs and their admixtures in pharmaceutical, urine and plasma samples. Maleic acid and sodium malate were used as internal standards. Effect of temperature on spectral measurements was evaluated. Linear dynamic ranges of 0.50-68.00, 0.13-11.30 and 0.24-21.00 mg per 0.60 mL solution were obtained for levofloxacin, metronidazole benzoate and sulfamethoxazole, respectively. Average recovery % in the range of 96.00-104.20 ± (0.17-2.91) was obtained for drugs in pure, pharmaceutical, plasma and urine samples. Inter and intra-day analyses gave average recoveries % in the ranges 96.10-98.40 ± (1.68-2.81) and 96.00-104.20 ± (0.17-2.91), respectively. Instrumental detection limits ≤0.03 mg per 0.6 mL were obtained for the three drugs. Developed method has demonstrated high performance characteristics for analyzing investigated drugs and their admixtures. Student t-test at 95% confidence level revealed insignificant bias between the real and measured contents of investigated drugs in pure, pharmaceutical, urine and plasma samples and its admixtures. Application of the statistical F-test revealed insignificant differences in precisions between the developed method and arbitrary selected reference methods.

Is a long-term ranitidine-based triple therapy against Helicobacter pylori only a heritage of the past? A prospective, randomized clinicopharmacological study

BACKGROUND

Acid suppression plus two antibiotics is currently considered the gold standard anti-Helicobacter pylori treatment, but the effective role of gastric antisecretory drugs is still poorly understood.

AIMS

To compare a 14-day ranitidine-based triple regimen against Helicobacter pylori with one based on omeprazole, and to study the influence of antisecretory drugs on metronidazole pharmacokinetics in human plasma.

METHODS

A total of 150 dyspeptic H. pylori-infected patients were randomized for ranitidine 300 mg b.d. (RCM group) or omeprazole 20 mg b.d. (OCM group) 14-day triple therapy, with clarithromycin 500 mg b.d. and metronidazole 500 mg b.d. On the eighth day of therapy, metronidazole pharmacokinetics was studied in plasma by high-performance liquid chromatography. The pharmacokinetic parameters (terminal half-life, area under the curve, peak-plasma level, peak time) of metronidazole were computed using standard non-compartmental methods. H. pylori status was monitored before and 4 weeks after the end of therapy by histology, serology and rapid urease test.

RESULTS

On an intention-to-treat basis, eradication rates were 91 and 76% for the RCM and OCM groups respectively (P < 0.02). Significantly different pharmacokinetic parameters of metronidazole were found between the groups: peak-plasma level (P < 0.01) and area under the curve (P < 0.02).

CONCLUSION

Our results show that the RCM regimen was more effective than that based on OCM and that the antisecretory drugs affected metronidazole availability, increasing the efficacy of ranitidine-based regimens.

Simultaneous determination of ranitidine and metronidazole in human plasma using high performance liquid chromatography with diode array detection

The development and validation of a simple method for the simultaneous determination of ranitidine and metronidazole in human plasma is described. Plasma samples (250 microL) were deproteinized by precipitation with 60% perchloric acid, centrifuged and the supernatant directly injected into the HPLC. Separation was achieved in isocratic mode with a Shimpak C(18) column and a mobile phase consisting of 10mM potassium dihydrogen phosphate pH 3.5:acetonitrile (90:10, v/v) with UV detection at 315 nm. The method showed good selectivity and sensitivity. Good and consistent recovery for metronidazole and ranitidine was obtained: 96.22+/-3.52 and 95.00+/-4.50% for ranitidine (25-1000 ng/mL) and metronidazole (60-10,000 ng/mL), respectively (n=3). With this one-step sample preparation method, both ranitidine and metronidazole could be quantified simultaneously in human plasma with good precision (R.S.D.<15%) and accuracy (bias values below 15%). The limit of quantification for ranitidine and metronidazole were 20 and 40 ng/mL plasma, respectively.

Formulation and evaluation of metronidazole acid gel for vaginal contraception

In this study, the efficacy of metronidazole as a local spermicidal agent was investigated. The drug was formulated in a concentration of 5% as an acid gel for vaginal application as a local contraception. The minimum spermicidal concentration of metronidazole was evaluated in-vitro and found to be 0.2% w/v. The formulated gel showed instant immobilization and death of all sperm within 30 s. A clinical study was conducted to determine the drug concentrations in vaginal secretions of healthy women and women with symptoms suggesting genital tract infection every 15 min for a 1-h period after application of 1 g of the gel in the vagina. Drug concentrations in the infected group were significantly lower (P < 0.05) than those in the healthy group at all time intervals. The drug concentrations in vaginal secretions after 1 h of vaginal medication remained above the determined minimum spermicidal concentration (0.2%) in the two groups. Measurement of vaginal pH before and after medication revealed a significant drop (P < 0.05) in pH to its normal value in both healthy and infected groups as a result of gel application. In conclusion, the designed gel has potential advantages of achieving a long retention time and effective drug concentrations in the vagina for at least 1 h after application, and of maintaining vaginal pH within its normal range.

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.

Pharmacokinetics and pharmacodynamics of the nitroimidazole antimicrobials

Metronidazole, the prototype nitroimidazole antimicrobial, was originally introduced to treat Trichomonas vaginalis, but is now used for the treatment of anaerobic and protozoal infections. The nitroimidazoles are bactericidal through toxic metabolites which cause DNA strand breakage. Resistance, both clinical and microbiological, has been described only rarely. Metronidazole given orally is absorbed almost completely, with bioavailability > 90% for tablets; absorption is unaffected by infection. Rectal and intravaginal absorption are 67 to 82%, and 20 to 56%, of the dose, respectively. Metronidazole is distributed widely and has low protein binding (< 20%). The volume of distribution at steady state in adults is 0.51 to 1.1 L/kg. Metronidazole reaches 60 to 100% of plasma concentrations in most tissues studied, including the central nervous system, but does not reach high concentrations in placental tissue. Metronidazole is extensively metabolised by the liver to 5 metabolites. The hydroxy metabolite has biological activity of 30 to 65% and a longer elimination half-life than the parent compound. The majority of metronidazole and its metabolites are excreted in urine and faeces, with less than 12% excreted unchanged in urine. The pharmacokinetics of metronidazole are unaffected by acute or chronic renal failure, haemodialysis, continuous ambulatory peritoneal dialysis, age, pregnancy or enteric disease. Renal dysfunction reduces the elimination of metronidazole metabolites; however, no toxicity has been documented and dosage alterations are unnecessary. Liver disease leads to a decreased clearance of metronidazole and dosage reduction is recommended. Recent pharmacodynamic studies of metronidazole have demonstrated activity for 12 to 24 hours after administration of metronidazole 1 g. The post-antibiotic effect of metronidazole extends beyond 3 hours after the concentration falls below the minimum inhibitory concentration (MIC). The concentration-dependent bactericidal activity, prolonged half-life and sustained activity in plasma support the clinical evaluation of higher doses of metronidazole given less frequently. Metronidazole-containing regimens for Helicobacter pylori in combination with proton pump inhibitors demonstrate higher success rates than antimicrobial regimens alone. The pharmacokinetics of metronidazole in gastric fluid appear contradictory to these results, since omeprazole reduces peak drug concentration and area under the concentration-time curve for metronidazole and its hydroxy metabolite; however, concentrations remain above the MIC. Other members of this class include tinidazole, ornidazole and secnidazole. They are also well absorbed and distributed after oral administration. Their only distinguishing features are prolonged half-lives compared with metronidazole. The choice of nitroimidazole may be influenced by the longer administration intervals possible with other members of this class; however, metronidazole remains the predominant antimicrobial for anaerobic and protozoal infections.

Metronidazole. A therapeutic review and update

The nitroimidazole antibiotic metronidazole has a limited spectrum of activity that encompasses various protozoans and most Gram-negative and Gram-positive anaerobic bacteria. Metronidazole has activity against protozoans like Entamoeba histolytica, Giardia lamblia and Trichomonas vaginalis, for which the drug was first approved as an effective treatment. Anaerobic bacteria which are typically sensitive are primarily Gram-negative anaerobes belonging to the Bacteroides and Fusobacterium spp. Gram-positive anaerobes such as peptostreptococci and Clostridia spp. are likely to test sensitive to metronidazole, but resistant isolates are probably encountered with greater frequency than with the Gram-negative anaerobes. Gardnerella vaginalis is a pleomorphic Gram-variable bacterial bacillus that is also susceptible to metronidazole. Helicobacter pylori has been strongly associated with gastritis and duodenal ulcers. Classic regimens for eradicating this pathogen have included metronidazole, usually with acid suppression medication plus bismuth and amoxicillin. The activity of metronidazole against anaerobic bowel flora has been used for prophylaxis and treatment of patients with Crohn's disease who might develop an infectious complication. Treatment of Clostridium difficile-induced pseudomembraneous colitis has usually been with oral metronidazole or vancomycin, but the lower cost and similar efficacy of metronidazole, coupled with the increased concern about imprudent use of vancomycin leading to increased resistance in enterococci, have made metronidazole the preferred agent here. Metronidazole has played an important role in anaerobic-related infections. Advantages to using metronidazole are the percentage of sensitive Gram-negative anaerobes, its availability as oral and intravenous dosage forms, its rapid bacterial killing, its good tissue penetration, its considerably lower chance of inducing C. difficile colitis, and expense. Metronidazole has notable effectiveness in treating anaerobic brain abscesses. Metronidazole is a cost-effective agent due to its low acquisition cost, its pharmacokinetics and pharmacodynamics, an acceptable adverse effect profile, and its undiminished antimicrobial activity. While its role as part of a therapeutic regimen for treating mixed aerobic/anaerobic infections has been reduced by newer, more expensive combination therapies, these new combinations have not been shown to have any therapeutic advantage over metronidazole. Although the use of metronidazole on a global scale has been curtailed by newer agents for various infections, metronidazole still has a role for these and other therapeutic uses. Many clinicians still consider metronidazole to be the 'gold standard' antibiotic against which all other antibiotics with anaerobic activity should be compared.

A liquid chromatography assay for the study of serum and gastric juice metronidazole concentrations in the treatment of Helicobacter pylori

Metronidazole is an important component of combination antimicrobial therapies used in the eradication of Helicobacter pylori, a recognized cause of gastritis and duodenal ulcer. Studies are needed to understand which pharmacokinetic factors determine the success of metronidazole therapy and what role drug monitoring plays. Such studies require a rapid, accurate assay for small volumes of sample, including gastric juice, over a 200-fold range of concentrations. Using an isocratic high-performance liquid chromatography (HPLC) method, with an 8-min run time and protein precipitation of samples, metronidazole could be measured reliably to as low as 0.5 mg/L in 100 microliters samples of serum, gastric juice, or saliva. Standard curves for serum and gastric juice were linear between 0.5 and 50 mg/L. Within-day coefficients of variation (CVs) (n = 5 at six concentrations) ranged from 1.1 to 4.8% over this range and the between-day CV (n = 7 days) was 5.8%. Neither omeprazole nor common gastroenteric and cardiac medications interfered with this assay. A pilot study, done in four healthy volunteers given intravenous metronidazole 500 mg before and after 7 days of omeprazole therapy, found metronidazole to be present in higher concentrations in gastric juice and saliva than in serum 2 h after intravenous administration. The range and accuracy of the assay proved to be suitable for carrying out pharmacokinetic studies at clinically used doses of the drug.

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

A rapid and selective HPLC method has been developed for the separation and quantitation of metronidazole and its hydroxylated metabolite in human plasma, saliva and gastric juice. The assay requires a simple protein precipitation step prior to analysis and is selective, sensitive and reproducible. The limits of quantitation (0.5-ml sample) were at least 0.25 microgram/ml for metronidazole and 0.20 micrograms/ml for its hydroxy metabolite. A Hypersil ODS 5 micron (150 x 4.5 mm I.D.) column was used with a mobile phase of acetonitrile-aqueous 0.05 M potassium phosphate buffer (pH 7) containing 0.1 % triethylamine (10:90) delivered at a flow-rate of 1.0 ml/min.

Bacterial mutagens in the urine of patients under tinidazole treatment

Tinidazole is an antiparasitic drug belonging to the 5-nitroimidazole family. It is prescribed against protozoal infestations and is widely used in Mexico as well as other underdeveloped countries where infectious diseases are the first cause of children mortality. The drug is a direct mutagen in Salmonella typhimurium TA100 strain and the presence of S9 mixture did not modify its mutagenic effect. At low doses no mutagenicity was detected with strains TA100NR, TA98 or UTH8414 (Uvr+ derivative of TA100). Urine from four patients under tinidazole treatment exhibited a mutagenic activity on strain TA100, greater than the expected from the tinidazole concentrations determined by high-performance liquid chromatography (HPLC). Components from the urine samples were separated on thin-layer chromatography (TLC) plates, and their mutagenic effects tested by direct application of the Salmonella assay onto sections of the developed chromatoplate. The Rf of one component (0.62) corresponded to the one obtained for a tinidazole standard and showed the expected mutagenicity, while a second component with an Rf=0.39, exhibited a mutagenic potency slightly greater than the observed for tinidazole; however, as in the case of the drug itself, reduction of the nitro group was necessary for a mutagenic activity.

Behavior of antibiotics during human necrotizing pancreatitis

The aim of the study was to verify whether antibiotics excreted by the normal pancreas are also excreted in human necrotizing pancreatitis, reaching the tissue sites of the infection. Twelve patients suffering from acute necrotizing pancreatitis were treated with imipenem-cilastatin (0.5 g), mezlocillin (2 g), gentamicin (0.08 g), amikacin (0.5 g), pefloxacin (0.4 g), and metronidazole (0.5 g). Serum and necrotic samples were collected simultaneously at different time intervals after parenteral drug administration by computed tomography-guided needle aspiration, intraoperatively, and from surgical drainages placed during surgery. Drug concentrations were determined by microbiological and high-performance liquid chromatography assays. All antibiotics reached the necrotic tissues, but with varying degrees of penetration, this being low for aminoglycosides (13%) and high in the case of pefloxacin (89%) and metronidazole (99%). The concentrations of pefloxacin (13.0 to 23 micrograms/g) and metronidazole (8.4 micrograms/g) in the necrotic samples were distinctly higher than the MICs for the organisms most commonly isolated in this disease; the concentrations in tissue of imipenem (3.35 micrograms/g) and mezlocillin (8.0 and 15.0 micrograms/g) did not always exceed the MICs for 90% of strains tested, whereas the aminoglycoside concentrations in necrotic tissue (0.5 microgram/g) were inadequate. Repeated administration of drugs (for 3, 7, 17, and 20 days) seems to enhance penetration of pefloxacin, imipenem, and metronidazole into necrotic pancreatic tissue. The choice of antibiotics in preventing infected necrosis during necrotizing pancreatitis should be based on their antimicrobial activity, penetration rate, persistence, and therapeutic concentrations in the necrotic pancreatic area. These requisites are provided by pefloxacin and metronidazole and to a variable extent by imipenem and mezlocillin.

Clinical pharmacokinetics of metronidazole and other nitroimidazole anti-infectives

Metronidazole was first introduced for the treatment of trichomoniasis. Its therapeutic use has subsequently been expanded to include amoebiasis, giardiasis and, more recently, anaerobic infections. Most of the early pharmacokinetic studies employed nonspecific assays such as microbiological and chemical assays. These assays were not able to differentiate the parent drug from the metabolites or other interfering substances. Pharmacokinetic data obtained through the use of specific chromatographic techniques provide the basis for this review of recent pharmacokinetic findings concerning metronidazole and other nitroimidazole antibiotics. When given intravenously or orally at usual recommended doses, metronidazole attains concentrations well above the minimum inhibitory concentrations for most susceptible micro-organisms. The drug has an oral bioavailability approaching 100%. Rectal and vaginal administration results in a smaller amount of drug absorption and lower serum concentrations. Metronidazole has limited plasma protein binding but can attain very favourable tissue distribution, including into the central nervous system. The drug is extensively metabolised by the liver to form 2 primary oxidative metabolites: the hydroxy and acetic acid metabolites. The kidney is responsible for the elimination of only a small amount of the parent drug; however, normal excretion of the 2 metabolites is dependent on the integrity of kidney function. The metabolism of metronidazole was found to vary among patient groups. Preterm and term infants have lower total body clearance (CL) and prolonged elimination half-lives. However, children older than 4 years old were observed to have pharmacokinetic parameters similar to those in adults. Reduced CL was also observed in children who are malnourished. Elderly patients have reduced renal excretion of both the parent drug and hydroxy metabolite. Pharmacokinetic parameters in pregnant patients were not significantly different from those in nonpregnant women; however, the drug is distributed into breastmilk and the infant will be exposed to the drug through the nursing mother. Patients undergoing gastrointestinal surgery or having enteric diseases and those who are hospitalised or critically ill also have altered pharmacokinetics. Metabolism of the drug is reduced in patients with liver dysfunction, giving delayed production of metabolites. In contrast, renal failure has little effect on the elimination of the parent drug, but affects the excretion of the metabolites more significantly. Haemodialysis was found to remove a substantial amount of the metronidazole while the effect of peritoneal dialysis was more limited. Energy and protein deficient diets as well as occupational exposure to gasoline did not alter metronidazole pharmacokinetics. However, the effect of alcohol consumption on metronidazole CL requires further study.(ABSTRACT TRUNCATED AT 400 WORDS)

Single-dose concentrations of tinidazole in gingival crevicular fluid, serum, and gingival tissue in adults with periodontitis

Previous studies have shown that metronidazole is effective in the treatment of subgingival microflora associated with destructive periodontitis. The aim of this study was to determine whether tinidazole, a close analogue of metronidazole, would reach sufficient concentrations in serum, gingival crevicular fluid, and gingival tissue, to inhibit putative periodontopathic bacteria. Ten adult patients with moderate to advanced periodontitis took a single 2-g dose of tinidazole orally. Samples were assayed by high-performance liquid chromatography. The concentrations of tinidazole in serum and GCF were in a similar range (3.2-46.5 micrograms/mL). Tinidazole was not detected in the GCF in three of the patients. The drug was found in gingival tissue obtained at two h (0.17 +/- 0.14 micrograms/mg) and six h (0.15 +/- 0.18 micrograms/mg) after oral administration. The mean concentration of tinidazole in serum at 24 h (13 +/- 3.0 micrograms/mL) is greater than the minimum inhibitory concentration for anaerobic bacteria as reported by others. The present data suggest that a single 2-g oral dose of tinidazole may lead to the presence of potentially bactericidal levels of tinidazole for up to 24 h in the periodontal pockets of some patients with periodontitis.

Pharmacokinetics and serum bactericidal activities of quinolones in combination with clindamycin, metronidazole, and ornidazole

To enhance the antimicrobial spectrum of the quinolones against anaerobic organisms and gram-positive bacteria, we investigated in two studies the parenteral combinations of ciprofloxacin (200 mg) and ofloxacin (200 mg) with metronidazole (500 mg) or clindamycin (600 mg) and the oral combinations of enoxacin (400 mg) and fleroxacin (400 mg) with metronidazole (400 mg), clindamycin (300 mg), or ornidazole (500 mg) (only with fleroxacin). The pharmacokinetics and serum bactericidal activities (SBAs) against 5 aerobic and 2 anaerobic species (total, 58 strains) were determined in two groups of 10 healthy volunteers by using a randomized crossover study design. The additions of metronidazole, clindamycin, and ornidazole did not affect the pharmacokinetics of the quinolones. The combination of clindamycin with ciprofloxacin, ofloxacin, and, to a lesser extent, fleroxacin resulted in an increase of the SBA against gram-positive strains (mean peak titers): Staphylococcus aureus, ciprofloxacin alone, 1:5.5; ciprofloxacin-clindamycin, 1:19.9; ofloxacin alone, 1:3.6; ofloxacin-clindamycin, 1:17.5; fleroxacin alone, 1:4.3; fleroxacin-clindamycin, 1:8.1; Streptococcus pneumoniae (fleroxacin and enoxacin were not tested), ciprofloxacin alone, 1:2.0; ciprofloxacin-clindamycin, 1:53; ofloxacin alone, 1:2.6; and ofloxacin-clindamycin, 1:49.2. The high SBA of quinolones against gram-negative bacteria was not affected by the combinations; however, relatively low activities against Pseudomonas aeruginosa were detected. In general, against anaerobic bacteria, low bactericidal activities were determined in both studies (mean peak titers ranged from 1:2.1 to 1:3.1; mean trough titers range from 1:2.0 to 1:2.9). In clinical settings with severe mixed infections, a parenteral therapy consisting of modern quinolones together with clindamycin or imidazole derivatives seems to be active and offers no obvious interactions.

High-performance liquid chromatography of antibiotics

High-performance liquid chromatographic (HPLC) monitoring of antimicrobial agents has recently become more widely used, and represents an interesting alternative to other methods. The methodology is characterized by good specificity and accuracy, and it is applicable to almost all antibiotics. This review first describes the successive steps to investigate for the development of an HPLC method for a new antibiotic, and how to make use of it. Particular emphasis is put on the problems related to the standardization of sample preparation and to the development of mobile phases for use with different molecules belonging to the same class. The second part of the review describes one or more HPLC techniques for a representative antibiotic of each major class.

Review article: metronidazole and the anaerobic gut flora

Metronidazole is a nitro-imidazole drug which was discovered nearly 30 years ago. Metronidazole has remained the mainstay of anti-anaerobic therapy following a change observation that its activity included anaerobic organisms. The predominant human reservoir of these anaerobic organisms is the gastrointestinal tract. In this review, the anaerobic flora and their pathogenic potential are described. The main characteristics of metronidazole and the role of selective decontamination of the gastrointestinal tract are also discussed.

Combination effects of ciprofloxacin, clindamycin, and metronidazole intravenously in volunteers

Despite the broad antibacterial spectrum of ciprofloxacin, most anaerobic organisms are resistant to the drug, whereas several gram-positive organisms are only moderately susceptible. Thus, in some clinical situations, combined treatment with ciprofloxacin and metronidazole or clindamycin could be useful. Therefore, the pharmacokinetics and serum bactericidal activities of ciprofloxacin in combination with clindamycin or metronidazole were investigated using a randomized crossover study design in 10 healthy volunteers. Ciprofloxacin (200 mg) was administered alone and in combination with clindamycin (600 mg) or metronidazole (500 mg); all drugs were given intravenously over 30 minutes. Serum and urine concentrations of the substances were measured using standard methods (high-performance liquid chromatography or gas chromatography). Blood samples for determination of serum bactericidal activity against five different aerobic and two anaerobic bacterial species (a total of 58 strains) were obtained one hour and six hours after drug infusion. All values were statistically analyzed by use of the Student t test.

The modes of action of some anti-protozoal drugs

In spite of the continuing need for new and improved anti-protozoal drugs for use in man, a considerable contraction of industrially based research on anti-protozoal drugs has occurred in recent years. Newton (1983) reviewed the reasons for this decline and presented a compelling argument that fundamental research on the biology of the parasites is essential for the discovery of leads for the development of a new generation of drugs – a rational chemotherapy. The rapid advance in knowledge of the biochemistry of parasitic protozoa which has occurred in recent years has provided a number of potential leads to new drug development and has permitted a greater understanding of the mode of action of many current drugs. The account of these advances which follows is necessarily selective and relates to protozoan parasites of man.

Tinidazole pharmacokinetics in severe renal failure

The single-dose pharmacokinetics of intravenously and orally administered tinidazole were studied in normal subjects and patients with severe chronic renal failure. The clearance of tinidazole was also measured in patients on regular haemodialysis. After intravenous administration the mean elimination half-life of tinidazole was 17.1 +/- 2.3 (SD) hours in the normal subjects and 16.9 +/- 4.9 hours in patients with renal failure; the mean apparent volumes of distribution were 0.80 +/- 0.09 L/kg and 0.69 +/- 0.09 L/kg, respectively. Following oral administration the mean elimination half-life was 15.6 +/- 1.6 hours in the normal subjects and 18.4 +/- 3.5 hours in patients with renal failure; there were no statistically significant differences in these pharmacokinetic parameters. There was no accumulation of the major metabolite (hydroxymethyl tinidazole) in normal subjects or in patients with renal failure. Tinidazole clearance during haemodialysis was 71 +/- 7.7 ml/min. In the presence of renal failure no modification of tinidazole dosage would appear to be necessary. Tinidazole should be administered in full dosage following haemodialysis.

Biological availability and pharmacokinetics of tinidazole after single and repeated doses

Tinidazole was administered to healthy volunteers and serum concentrations were measured following single oral and intravenous doses and after repeated dosage at different dose levels. The elimination half-time was 12-13 h. Pharmacokinetics did not change with dose, route of administration or repeated dosage. The bioavailability of single oral doses ranged between 88 and 129% with a mean of 99%. Serum concentration curves tended to have double peaks or plateaus at about 4-6 h. 74% of the intravenous dose was eliminated from serum at 24 h, but only 19% was recovered in the urine, suggesting alternative ways of elimination. Excretion in the bile and a subsequent enterohepatic circulation may explain the variations in bioavailability and the shape of the serum concentration curves.

Pharmacokinetics of tinidazole in chronic renal failure and in patients on haemodialysis

The pharmacokinetics of tinidazole after infusion (800 mg in 15 min) were studied in 12 patients with chronic renal failure (RI) and in five patients undergoing regular dialysis treatment (RD). Tinidazole elimination plasma half-life was 15.09 +/- 0.68 h (mean +/- s.e. mean) (RI) and 12.9 +/- 1.0 h after dialysis (RD), but there was a significant decrease in half-life during dialysis (4.25 +/- 0.43 h) P less than 0.001). The apparent volume of distribution (0.64 +/- 0.03 l/kg) was equal to extra and intracellular water volume and tinidazole was little bound to plasma protein (8%). There was a slight sex difference in apparent volume of distribution between male patients (0.70 +/- 0.09 l/kg) and female patients (0.59 +/- 0.10 l/kg) (P = 0.07), but as body clearance decreases in the same order, there was no modification of plasma half-life. In renal failure, pharmacokinetics of tinidazole were not disturbed because no correlation between half-life, body clearance and creatinine clearance occurred; urine elimination was about 7% of administered dose. Plasma clearance during dialysis was 49.9 +/- 3.2 ml/min and about 43% of the available drug was eliminated during the 6 h dialysis procedure. These results suggest that an additional half-dose infusion should be given after the end of dialysis in patients undergoing regular dialysis treatment.

Tinidazole--microbiology, pharmacology and efficacy in anaerobic infections

Tinidazole is a 5-nitroimidazole with selective activity against anaerobic bacteria and protozoa. It is bactericidal at low concentrations and its spectrum covers most anaerobic bacteria and some capnophilic microorganisms. Anaerobic bacteria known to be resistant to tinidazole include anaerobic streptococci, actinomyces and propionibacteria. Tinidazole is one of the most active antibacterial agents against Bacteroides fragilis which is one of the most resistant species of anaerobic bacteria. Only a few strains have been reported to be resistant. Tinidazole has been shown to be efficacious in protozoal infections such as trichomonal vaginitis, amoebiasis and giardiasis. Clinical studies have also shown that tinidazole is efficacious in the treatment of anaerobic infections including respiratory tract infections, intra-abdominal sepsis and obstetrical and gynecological infections. Since tinidazole has no activity against aerobic bacteria, it must be combined with other antibacterial agents in the treatment of mixed infections involving aerobic and anaerobic bacteria. Tinidazole has also been used successfully alone or in combination with other antimicrobial agents for prophylaxis in patients undergoing elective colonic and abdominal surgery, emergency appendectomy and gynecological surgery.

Mental confusion in a patient treated with metronidazole--a concentration-related effect?

We report a case of serious mental confusion, hallucinations, and agitation in a 65 year old man, occurring in close relationship to the intravenous administration of metronidazole. The patient was treated twice, but at different dosages. The confusion and hallucinations occurred at the recommended daily dose of 2.0 g, but did not return at a daily dose of 500 mg. Metronidazole serum concentrations were obtained throughout both courses of therapy; CSF and tissue concentrations were obtained at autopsy. The mental confusion was associated with peak serum concentrations of approximately 40 micrograms/ml. Symptoms resolved within 24-48 hr after stopping metronidazole, and resolution was consistent with a metronidazole half life of 14 hr. We conclude that metronidazole can be associated with a dose- and serum concentration-related mental confusion state, and that this side effect appears completely reversible upon discontinuing the drug.

Activity of metronidazole and its hydroxy and acid metabolites against clinical isolates of anaerobic bacteria

Susceptibility of clinical isolates of anaerobic bacteria to metronidazole and its two oxidation products, 1-(2-hydroxyethyl)-2-hydroxymethyl-5-nitroimidazole (the "alcohol" metabolite) and 2-methyl-5-nitroimidazole-1-acetic acid (the "acid" metabolite), were determined by the agar dilution technique. Results disclosed that the alcohol metabolite, although less active than metronidazole, inhibited the organisms tested at levels considered susceptible for metronidazole. The acid metabolite was less active, not inhibiting the organisms at levels within the susceptible range. In other studies, mixtures of known concentrations of metronidazole and the metabolites were assayed in a bioassay system used to measure metronidazole levels. These studies showed that the bioassay will measure metronidazole or the alcohol metabolite; the acid metabolite is not measured at levels achieved in clinical specimens. Since the activity of the alcohol metabolite is comparable to that of metronidazole, we feel that microbiological assays can be used for therapeutic monitoring of metronidazole levels in clinical situations.

Tinidazole in anaerobic infections: a review of its antibacterial activity, pharmacological properties and therapeutic efficacy

Tinidazole, like the structurally-related drug metronidazole, was initially introduced for treating protozoal infections. However, both these nitroimidazole compounds are also active in vitro against most clinically important obligate anaerobes. Most of the clinical experience with tinidazole to date has involved prophylactic use to prevent postoperative anaerobic infection. Prospective placebo-controlled studies demonstrated that a single dose of tinidazole administered orally prior to elective colorectal surgery significantly reduced postoperative infection. Similarly, when given intravenously prior to appendectomy, tinidazole reduced the incidence of postoperative infection in some subgroups of patients. Although results of non-blinded studies with prophylactic tinidazole were encouraging when used in women undergoing gynaecological surgery (mainly hysterectomy), results from double-blind placebo-controlled studies in this situation have been somewhat equivocal. Thus, although the overall weight of evidence suggests that the drug is effective in this area of use, further study is needed to clarify its role in preventing anaerobic infection following gynaecological surgery compared with other antibiotics which can also be used for this purpose. Relatively few studies have been conducted with tinidazole in the treatment of established anaerobic infections, and this is an area needing further investigation. The drug is well tolerated when administered orally or intravenously.

In vitro activity of the two principal oxidative metabolites of metronidazole against Bacteroides fragilis and related species

Metronidazole and its two principal oxidative metabolites were tested in vitro against 20 clinical isolates of the Bacteroides fragilis group. Both metabolites were bactericidal, and the exhibited 65 and 5%, respectively, of the inhibitory effect of metronidazole. Additive or weak synergistic effects resulted in combination with the parent compound.