Pharmacokinetics and pharmacodynamics of intravenous levofloxacin at 750 milligrams and various doses of metronidazole in healthy adult subjects

Metronidazole promotes oxidative stress and DNA fragmentation-mediated myocardial injury in albino mice

The purpose of the present study was to investigate the cardiotoxic effects of Metronidazole (Mtz) in albino mice. The mice were divided into four experimental groups: Gp.I (control group): saline, Gp.II:125 mg/kg b.w Mtz, Gp.III:250 mg/kg b.w, Gp.IV:500 mg/kg b.w Mtz. Heart weight ratio, markers of cardiac injury, markers of oxidative stress, histopathological examinations, DNA fragmentation and spectral analysis were used to determine cardiotoxicity. Administration of 125-500 mg/kg Mtz caused an increase in heart weight and a decrease in body weight. Administration of 500 mg/kg Mtz increased heart weight by 35.5% and decreased body weight by 21.9% compared with control. Mtz-treated mice showed a significant increase in cardiac injury biomarkers and serious alterations in cardiac oxidative stress markers. Histopathological changes of cardiac tissues observed in mice treated with Mtz include myocardial hypertrophy, fibrosis, myocarditis, separation of the muscle fibers, congestion-narrowing in vessels, necrosis, myocardium-vacuolation, myocytolysis, myocyte degeneration, nuclear aggregation, cytoplasmic fragmentation and prevalent nuclei. Mtz treatment already resulted in a significant decrease in the percentage of head DNA and an increase in the percentage of tail DNA. The most striking tail formation among the Mtz-treated groups was observed in the group receiving 500 mg/kg Mtz. In the presence of Mtz, there was a hypochromic shift in the absorption spectrum of DNA, and the potential DNA-Mtz interaction was found to occur in the intercalation mode. These results show that Mtz used against anaerobic bacteria and protozoa in gastrointestinal infections can cause severe cardiotoxic findings in albino mice and cause fragmentation in DNA.

Pharmacokinetic and Pharmacodynamic Properties of Metronidazole in Pediatric Patients With Acute Appendicitis: A Prospective Study

BACKGROUND

Metronidazole is traditionally dosed every 6-8 hours even though in adults it has a long half-life, concentration-dependent killing, and 3-hour postantibiotic effect. Based on this logic, some pediatric hospitals adopted once-daily dosing for appendicitis, despite limited pharmacokinetics-pharmacodynamics (PK/PD) in children. We studied pediatric patients with appendicitis given metronidazole once daily to determine whether this dosing would meet target area under the curve (AUC)/minimum inhibitory concentration (MIC) ratio of ≥70 for Bacteroides fragilis.

METHODS

One hundred pediatric patients aged 4-17 years had an average of 3 blood draws per patient during the first 24 hours after a 30 mg/kg per dose of intravenous metronidazole. Concentrations of drug were determined using validated liquid chromatography and tandem mass spectrometry. A NONMEM model was constructed for determining PK, followed by Monte Carlo simulations to generate a population of plasma concentration-time AUC of metronidazole and hydroxy-metronidazole.

RESULTS

Simulated AUC values met target attainment (AUC/MIC ratio of ≥70 to B fragilis MICs) for 96%-100% of all patients for an MIC of 2 mcg/mL. For MICs of 4 and 8 mcg/mL, target attainment ranged from 61% to 97% and 9% to 71%, respectively. Areas under the curve were similar to that of adults receiving 1000 mg and 1500 mg q24, or 500 mg q8 hours.

CONCLUSIONS

Metronidazole, 30 mg/kg per dose, once daily achieved AUC target attainment for B fragilis with an MIC of 2 mcg/mL or less in pediatric appendicitis patients. Based on this and studies in adults, there does not seem to be any PK/PD advantage of more frequent dosing in this population.

Identifying 24 h variation in the pharmacokinetics of levofloxacin: a population pharmacokinetic approach

AIM

The objective of this study was to investigate whether the pharmacokinetics of orally administered levofloxacin show 24 h variation. Levofloxacin was used as a model compound for solubility and permeability independent absorption and passive renal elimination.

METHODS

In this single centre, crossover, open label study, 12 healthy subjects received an oral dose of 1000 mg levofloxacin at six different time points equally divided over the 24 h period. Population pharmacokinetic modelling was used to identify potential 24 h variation in the pharmacokinetic parameters of this drug.

RESULTS

The pharmacokinetics of levofloxacin could be described by a one compartment model with first order clearance and a transit compartment to describe drug absorption. The fit of the model was significantly improved when the absorption rate constant was described as a cosine function with a fixed period of 24 h, a relative amplitude of 47% and a peak around 08.00 h in the morning. Despite this variation in absorption rate constant, simulations of a once daily dosing regimen showed that tmax , Cmax and the area under the curve at steady-state were not affected by the time of drug administration.

CONCLUSION

The finding that the absorption rate constant showed considerable 24 h variation may be relevant for drugs with similar physicochemical properties as levofloxacin that have a narrower therapeutic index. Levofloxacin, however, can be dosed without taking into account the time of day, at least in terms of its pharmacokinetics.

Prediction of the pharmacokinetics and tissue distribution of levofloxacin in humans based on an extrapolated PBPK model

This study developed a physiologically based pharmacokinetic (PBPK) model in intraabdominally infected rats and extrapolated it to humans to predict the levofloxacin pharmacokinetics and penetration into tissues. Twelve male rats with intraabdominal infections induced by Escherichia coli received a single dose of 50 mg/kg body weight of levofloxacin. Blood plasma was collected at 5, 10, 20, 30, 60, 120, 240, 480 and 1440 min after injection, respectively. A PBPK model was developed in rats and extrapolated to humans using GastroPlus software. The predictions were assessed by comparing predictions and observations. In the plasma concentration-versus-time profile of levofloxacin in rats, C max was 23.570 μg/ml at 5 min after intravenous injection, and t1/2 was 2.38 h. The plasma concentration and kinetics in humans were predicted and validated by the observed data. Levofloxacin penetrated and accumulated with high concentrations in the heart, liver, kidney, spleen, muscle and skin tissues in humans. The predicted tissue-to-plasma concentration ratios in abdominal viscera were between 1.9 and 2.3. When rat plasma concentrations were known, extrapolation of a PBPK model was a method to predict the drug pharmacokinetics and penetration in humans. Levofloxacin had good penetration into the liver, kidney and spleen as well as other tissues in humans. This pathological model extrapolation may provide a reference for the study of antiinfective PK/PD. In our study, levofloxacin penetrated well into abdominal organs. Also ADR monitoring should be implemented when using levofloxacin.

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.

Pharmacokinetics and pharmacodynamics of levofloxacin injection in healthy Chinese volunteers and dosing regimen optimization

WHAT IS KNOWN AND OBJECTIVE

The pharmacokinetics (PK) and pharmacodynamics (PD) of levofloxacin were investigated following administration of levofloxacin injection in healthy Chinese volunteers for optimizing dosing regimen.

METHODS

The PK study included single-dose (750 mg/150 mL) and multiple-dose (750 mg/150 mL once daily for 7 days) phases. The concentration of levofloxacin in blood and urine was determined using HPLC method. Both non-compartmental and compartmental analyses were performed to estimate PK parameters. Taking fC(max) /MIC ≥5 and fAUC(24 h) /MIC ≥30 as a target, the cumulative fraction of response (CFR) of levofloxacin 750 mg for treatment of community-acquired pneumonia (CAP) was calculated using Monte Carlo simulation. The probability of target attainment (PTA) of levofloxacin at various minimal inhibitory concentrations (MICs) was also evaluated.

RESULTS AND DISCUSSION

The results of PK study showed that the C(max) and AUC(0-∞) of levofloxacin were 14·94 μg/mL and 80·14 μg h/mL following single-dose infusion of levofloxacin. The half-life and average cumulative urine excretion ratio within 72 h post-dosing were 7·75 h and 86·95%, respectively. The mean C(ss,max), C(ss,min) and AUC(0-τ) of levofloxacin at steady state following multiple doses were 13·31 μg/mL, 0·031 μg/mL and 103·7 μg h/mL, respectively. The accumulation coefficient was 1·22. PK/PD analysis revealed that the CFR value of levofloxacin 750-mg regimen against Streptococcus pneumoniae was 96·2% and 95·4%, respectively, in terms of fC(max) /MIC and fAUC/MIC targets.

WHAT IS NEW AND CONCLUSION

The regimen of 750-mg levofloxacin once daily provides a satisfactory PK/PD profile against the main pathogenic bacteria of CAP, which implies promising clinical and bacteriological efficacy for patients with CAP. A large-scale clinical study is warranted to confirm these results.

Clinical pharmacology and lesion penetrating properties of second- and third-line antituberculous agents used in the management of multidrug-resistant (MDR) and extensively-drug resistant (XDR) tuberculosis

Failure of first-line chemotherapy to cure tuberculosis (TB) patients occurs, in part, because of the development of resistance to isoniazid (INH) and rifampicin (RIF) the two most sterilizing agents in the four-drug regimen used to treat primary infections. Strains resistant to both INH and RIF are termed multidrug-resistant (MDR). Treatment options for MDR patients involve a complex array of twenty different drugs only two classes of which are considered to be highly effective (fluoroquinolones and aminoglycosides). Resistance to these two classes results in strains known as extensively drug-resistant (XDR) and these types of infections are becoming increasingly common. Many of the remaining agents have poorly defined pharmacology but nonetheless are widely used in the treatment of this disease. Several of these agents are known to have highly variable exposures in healthy volunteers and little is known in the patients in which they must be used. Therapeutic drug monitoring (TDM) is infrequently used in the management of MDR or XDR disease yet the clinical pharmacokinetic studies that have been done suggest this might have a large impact on disease outcome. We review what is known about the pharmacologic properties of each of the major classes of second- and third-line antituberculosis agents and suggest where judicious use of TDM would have the maximum possible impact. We summarize the state of knowledge of drug-drug interactions (DDI) in these classes of agents and those that are currently in clinical trials. Finally we consider what little is known about the ability of TB drugs to reach their ultimate site of action--the interior of a granuloma by penetrating the diseased lung area. Careful consideration of the pharmacology of these agents is essential if we are to avoid further fueling the growing epidemic of highly drug-resistant TB and critical in the development of new antituberculosis drugs.

Levofloxacin : a review of its use as a high-dose, short-course treatment for bacterial infection

Levofloxacin (Levaquin) is a fluoroquinolone antibacterial that is the L-isomer of ofloxacin. A high-dose (750 mg) short-course (5 days) of once-daily levofloxacin is approved for use in the US in the treatment of community-acquired pneumonia (CAP), acute bacterial sinusitis (ABS), complicated urinary tract infections (UTI) and acute pyelonephritis (AP). The broad spectrum antibacterial profile of levofloxacin means that monotherapy is often a possibility in patients with CAP at times when other agents may require combination therapy, although levofloxacin can be used in combination therapy when necessary. The high-dose, short-course levofloxacin regimen maximizes its concentration-dependent bactericidal activity and may reduce the potential for resistance to emerge. In addition, this regimen lends itself to better compliance because of the shorter duration of treatment and the convenient once-daily administration schedule. Oral levofloxacin is rapidly absorbed and is bioequivalent to the intravenous formulation; importantly, patients can transition between the formulations, which results in more options in regards to the treatment regimen and the potential for patients with varying degrees of illness to be treated. Levofloxacin has good tissue penetration and an adequate concentration can be maintained in the urinary tract to treat uropathogens. Levofloxacin is generally well tolerated and has good efficacy in the treatment of patients with CAP, ABS, complicated UTI and AP. The efficacy and tolerability of levofloxacin 500 mg once daily for 10 days in patients with CAP, ABS and UTIs is well established, and the high-dose, short-course levofloxacin regimen has been shown to be noninferior to the 10-day regimen in CAP and ABS, and to have a similar tolerability profile. Similarly, the high-dose, short-course levofloxacin regimen is noninferior to ciprofloxacin in patients with complicated UTI or AP. Thus, levofloxacin is a valuable antimicrobial agent that has activity against a wide range of bacterial pathogens; however, its use should be considered carefully so that the potential for resistance selection can be minimized and its usefulness in severe infections and against a range of penicillin- and macrolide-resistant pathogens can be maintained.

Stability of cefepime and metronidazole prepared for simplified administration as a single product

The stabilities of cefepime and metronidazole were determined after preparation of a single admixture product in view of its potential use as a simple and cost-effective therapeutic alternative for infections caused by many aerobic and anaerobic pathogens. The stability of cefepime 1000 or 2000 mg mixed with metronidazole 500 or 1500 mg was evaluated via high-performance liquid chromatography after storage for up to 336 h at 4 or 23 degrees C. Cefepime was stable in all 4 degrees C samples for up to 336 h, retaining > or =95% of initial concentrations. Samples of cefepime 1000 and 2000 mg mixed with metronidazole 500 mg were stable at 23 degrees C for up to 48 h, whereas those mixed with metronidazole 1500 mg and cefepime controls were stable at 23 degrees C for up to 72 h. Metronidazole was stable in all samples for up to 336 h, retaining > or =94% of initial concentrations. These data suggest that therapeutic use of cefepime and metronidazole as a single intravenous admixture product is feasible and practical.

Population pharmacokinetic modeling and Monte Carlo simulation of varying doses of intravenous metronidazole

Population pharmacokinetic modeling and Monte Carlo simulation (MCS) are approaches used to determine probability of target attainment (PTA) of antimicrobial therapy. The objectives of this study were 1) to determine a population pharmacokinetic model (PPM) using metronidazole and hydroxy-metronidazole concentrations from healthy subjects and critically ill patients, and 2) to determine the probability of attaining the pharmacodynamic target area under the plasma concentration (AUC)/MIC ratio >or=70 against 218 clinical isolates of Bacteroides fragilis using MCS. Eighteen healthy subjects were randomized to 3 dosages of intravenous metronidazole (500 mg every 8 h, 1000 mg day(-1), 1500 mg day(-1)) in an open-label 3-way crossover fashion. Serial blood samples were collected over 25.5 h on the 3rd day of each study period. An additional of 8 critically ill patients received intravenous metronidazole 500 mg every 8 h. Serial blood samples were collected over 8 h after the 2nd day of dosing. Plasma metronidazole and hydroxy-metronidazole concentrations were analyzed using a high-performance liquid chromatographic assay. The 834 plasma concentrations from 62 data sets were simultaneously modeled with Non-Parametric Adaptive Grid population modeling program. A 4-compartment model with a metabolite and zero-order infusion into the central compartment was used. The mean parameter vector and covariance matrix from PPM were inserted into the simulation module of ADAPT II. A 10,000-subject MCS was performed to determine the probability of PTA for a total drug AUC to MIC ratio >or=70 against 218 isolates of B. fragilis (MIC range, 0.125-2.0 mg L(-1)). Mean parameter values were CL(non-OH), 3.08 L h(-1); Vc, 35.4 L; K(OH), 0.04 h(-1); CL(OH), 2.78 L h(-1); and V(OH), 9.66 L. The regression values of the observed versus predicted concentrations (r2) of metronidazole and hydroxy-metronidazole were 0.972 and 0.980, respectively. The PTA for metronidazole 1500 mg day(-1) or 500 mg every 8 h (taken together) and 1000 mg day(-1) were 99.9% and 99.8%, respectively, over the reported MIC distribution range. For an MIC of 4 mg L(-1), the predicted PTA decreased to 80.0% and 28.5%, respectively. A PPM was determined by comodeling metronidazole and hydroxy-metronidazole concentrations from healthy subjects and critically ill patients. Based on this model, attainment of the target pharmacodynamic parameter (AUC/MIC ratio >or=70) against B. fragilis isolates is >99% when MICs are <2 mg L(-1), irrespective of the dosing interval of 24 h.

Intrapulmonary pharmacokinetics and pharmacodynamics of high-dose levofloxacin in healthy volunteer subjects

The objective of this study was to determine the plasma and intrapulmonary pharmacokinetic parameters of intravenously administered levofloxacin in healthy volunteers. Three doses of either 750 mg or 1000 mg levofloxacin were administered intravenously to 4 healthy adult subjects (750 mg) to 20 healthy adult subjects divided into five groups of 4 subjects (1000 mg). Standardised bronchoscopy and timed bronchoalveolar lavage (BAL) were performed following administration of the last dose. Blood was obtained for drug assay prior to drug administration and at the time of BAL. Levofloxacin was measured in plasma, BAL fluid and alveolar cells (ACs) using a sensitive and specific combined high-performance liquid chromatographic tandem mass spectrometric technique (HPLC/MS/MS). Plasma, epithelial lining fluid (ELF) and AC pharmacokinetics were derived using non-compartmental methods. The maximum plasma drug concentration to minimum inhibitory concentration ratio (C(max)/MIC(90)) and the area under the drug concentration curve to minimum inhibitory concentration ratio (AUC/MIC(90)) during the dosing interval were calculated for potential respiratory pathogens with MIC(90) values from 0.03 microg/mL to 2 microg/mL. In the 1000 mg dose group, the C(max) (mean+/-standard deviation (S.D.)), AUC(0-8h) and half-life were: for plasma, 9.2+/-1.9 microg/mL, 103.6 microg h/mL and 7.45 h; for ELF, 25.8+/-7.9 microg/mL, 279.1 microg h/mL and 8.10h; and for ACs, 51.8+/-26.2 microg/mL, 507.5 microg h/mL and 14.32 h. In the 750 mg dose group, the C(max) values in plasma, ELF and ACs were 5.7+/-0.4, 28.0+/-23.6 and 34.2+/-18.7 microg/mL, respectively. Levofloxacin concentrations were significantly higher in ELF and ACs than in plasma at all time points. For pathogens commonly associated with community-acquired pneumonia, C(max)/MIC(90) ratios in ELF ranged from 12.9 for Mycoplasma pneumoniae to 859 for Haemophilus influenzae, and AUC/MIC(90) ratios ranged from 139 to 9303, respectively. The C(max)/MIC(90) ratios in ACs ranged from 25.9 for M. pneumoniae to 1727 for H. influenzae, and AUC/MIC(90) ratios ranged from 254 to 16917, respectively. The C(max)/MIC(90) and AUC/MIC(90) ratios provide a pharmacokinetic rationale for once-daily administration of a 1000 mg dose of levofloxacin and are favourable for the treatment of community-acquired respiratory pathogens.

Fluoroquinolones and Anaerobes

The usefulness of fluoroquinolones for the treatment of mixed aerobic and anaerobic infections has been investigated since these agents started being used in clinical practice. Newer compounds have increased in vitro activity against anaerobes, but clinically relevant susceptibility breakpoints for these bacteria have not been established. Pharmacodynamic analyses and corroboration by new data from clinical trials have enhanced our knowledge concerning the use of fluoroquinolones to treat selective anaerobic pathogens. These studies suggest that newer agents could be useful in the treatment of several types of mixed aerobic and anaerobic infections, including skin and soft-tissue, intra-abdominal, and respiratory infections. The major concerns with expanding the use of fluoroquinolones to treat anaerobic infections have been reports of increasing resistance in Bacteroides group isolates and the impact of these antibiotics on the incidence of Clostridium difficile-associated disease.