Department of Pediatrics, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75235-9063, USA
![]() |
Abstract |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The activity of quinolones best correlates with area under the concentration curve (AUC)/MIC in experimental sepsis when survival is used as an endpoint. 5 In experimental meningitis, activity, defined by bacterial killing rate in CSF, correlated with peak concentration (C max)/MBC. 6 However, the pharmacodynamic properties of trovafloxacin in CSF have not been studied in detail. The purpose of this study was to determine the pharmacodynamic profile of trovafloxacin in CSF in experimental penicillin- and cephalosporin-resistant pneumococcal meningitis and to determine the dosing regimen necessary for optimal bacterial killing that could be implemented for treatment of children with bacterial meningitis.
![]() |
Materials and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
A type 6B strain of S. pneumoniae originally isolated from an infant with meningitis was used for all experiments. 7 After intrathecal passage in rabbits, the strain was grown overnight on blood agar plates. The plates were washed with phosphate-buffered saline (PBS), and aliquots of the resultant suspension were frozen at -70°C. For preparation of the inoculum, aliquots were diluted in PBS to a concentration of approximately 5 x 10 5 cfu/mL of which 250 µL was injected intracisternally into each rabbit. The inoculum size was confirmed by quantitative cultures in each experiment.
Susceptibility tests
The MICs and MBCs of different antibiotics were measured in Mueller-Hinton broth supplemented with 3-5% lysed horse blood by a standard microdilution method. 8
Meningitis model
The rabbit meningitis model, modified from the original description by Dacey & Sande, 9 was used. New Zealand white male rabbits weighing 2- 2.5 kg were anaesthetized with intramuscular ketamine (50 mg/kg) and acepromazine (4 mg/kg) before every procedure. Flunixin meglumine (1.1 mg/kg) was administered intramuscularly every 12 h for analgesia. Animals were immobilized in stereotactic frames, and a spinal needle was introduced into the cisterna magna to withdraw 250 µL of CSF and to inject an equal volume of the bacterial inoculum (approximately 1 x 10 5). Treatment was initiated 16-18 h after inoculation (0 h) once CSF was withdrawn for quantification of the initial bacterial concentration. Animals were killed with pentobarbital (120 mg/kg) at the end of each experiment or earlier if they appeared severely lethargic or were unable to maintain recumbency.
Treatment
Alatrofloxacin, the prodrug of trovafloxacin (Pfizer Central Research, Groton, CT, USA), was administered as an intravenous bolus to rabbits and protected from light during preparation and infusion. In the first experiment, single doses of 10 mg/kg (n = 6), 15 mg/kg (n = 7), 20 mg/kg (n = 8) or 30 mg/kg (n = 8) were infused at 0 h. In the second experiment, rabbits were given an initial loading dose of 20 mg/kg followed by either 15 mg/kg at 4 h (n = 18) or 10 mg/kg at 2, 4 and 6 h (n = 13). These dosing intervals were chosen on the basis of previous animal studies showing the serum half-life of trovafloxacin to be 2 h. 10
Sample collection and processing
For purposes of sampling, animals in the first experiment were immobilized in stereotactic frames with intracisternal needles in place for the first 6 h. The experiments were designed to limit the number of interventions per animal and to minimize any effect that removal of CSF, either in terms of frequency or volume, may have on the dynamics of CSF flow and on antibiotic concentrations. CSF (100 µL) samples were collected at 1, 2, 3, 4, 6,12 and 24 h after the beginning of treatment. Blood samples (0.5-1.0 mL) were collected at 0.5, 1, 2, 3, 4 and 6 h. Sample times were chosen based on previous animal studies showing the peak of trovafloxacin in CSF to be 1 h and in serum to be 0.5 h. 10 Animals in the second experiment were divided into two treatment groups. The first treatment group (treated four times) had CSF samples collected at 1, 2, 3, 4, 5, 6, 7, 24 and 48 h and blood at 0.5, 1, 2, 2.5, 3, 4, 4.5, 5, 6 and 6.5 h. The second treatment group (treated twice) had CSF samples collected at 1, 4, 5, 24 and 48 h and blood at 0.5, 1, 4 and 4.5 h. CSF and blood samples were centrifuged at 5000g for 5 and 10 min, respectively, and the supernatants were stored at -70°C until determination of antibiotic concentrations. CSF specimens visibly contaminated with blood were excluded from analysis.
An additional 100-150 µL aliquot of CSF was collected for quantification of bacterial concentrations at 0, 3, 6, 12 and 24 h (experiment 1) and 0, 4, 24 and 48 h (experiment 2). Bacterial concentrations were quantified by plating undiluted and serial dilutions of CSF (100 µL) on sheep blood agar and incubating in 5% CO 2 at 35°C for 24 h. The lowest bacterial concentration detectable by this method was 10 cfu/mL. For purposes of analysis, specimens with <10 cfu/mL were assigned a value of 10 (1 log 10) cfu/mL.
Antibiotic assays
Trovafloxacin concentrations were determined by disc diffusion microbioassay using Bacillus subtilis ATCC 6633. 11 The lower limit of detection was 0.2 mg/L. Inter- and intra-assay coefficients of variation were <10% for both serum and CSF.
Pharmacodynamic calculations
Pharmacodynamic indices were calculated based on serum and CSF trovafloxacin concentrations
measured from 1 to 12 h (experiment 1) after infusion of trovafloxacin. Calculations were
performed using Top Fit 2.0 (Karl Thomae, Boehringer Ingelheim, Germany). A
two-compartment model (with lag-time) was used for calculations of blood pharmacokinetic
indices and a non-compartmental model for CSF pharmacokinetics. Data from each animal were
calculated individually for the CSF analyses. Because of infrequent sampling in the -phase
the half-lives (t
½) and area under the concentration-time curves for serum were
calculated based on mean values of each dosage group. The AUCs were estimated to the last
quantifiable concentration using the logarithmic trapezoidal rule and extrapolated to infinity
using terminal-phase rate constant. Time of concentration above MBC (T> MBC)
was calculated using a logarithmic regression line. AUC/MBC was calculated as a ratio, as was C
max/MBC.
Statistical analysis
To assess correlations between pharmacokinetic indices (AUC/MBC, C max/MBC, T> MBC) and bacterial killing rates, data were fitted to an asymmetrical sigmoid curve using the Hill equation (Sigma Plot, SPSS, Inc., Chicago, IL, USA).
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
For the pneumococcal strain used, the MICs and MBCs, respectively, of both penicillin and ceftriaxone were 4.0 mg/L and 4.0 mg/L and of trovafloxacin, 0.06 mg/L and 0.125 mg/L.
Antibiotic concentrations
Mean serum and CSF trovafloxacin concentrations measured 30 min to 6 h after one dose are presented in Table I. Concentrations at 12 h and 24 h were below the level of detection. The highest CSF and serum concentrations were measured 1 h and 30 min, respectively, after drug administration and were considered the peak concentrations.
|
The serum and CSF half-lives of trovafloxacin were similar in all treatment groups although there was a trend of increasing CSF half-life values with increased dosages (Table II). The mean values for penetration of trovafloxacin into the CSF (AUC CSF/AUC serum) were from 21 to 27%.
|
Mean CSF concentrations of S. pneumoniae measured in animals treated with single doses of trovafloxacin are shown in Figure 1. Initial mean bacterial concentrations were similar for all groups. Mean maximal reductions in bacterial titres (log 10 cfu/mL) were -1.82 ± 1.68, -2.74 ± 0.22, -3.27 ± 1.10 and -4.89 ± 0.92 at 12 h for animals receiving 10, 15, 20 and 30 mg/kg, respectively.
|
|
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Drusano et al., using lomefloxacin in the neutropenic sepsis rat model, showed that AUC/MIC was most closely linked to clinical outcome; however, when C max/MIC ratios were >10:1, C max/MIC was the most accurate indicator. 14 We were unable to achieve consistently C max/MIC ratios above 10:1 in CSF (C max/MBC > 5 for our strain of S. pneumoniae) precluding validation of that observation. Forrest et al., using ciprofloxacin in seriously ill patients, determined that among pharmacodynamic variables the AUC/ MIC ratio was the most important predictor of outcome. 15 This study was conducted in patients with lower respiratory tract, soft tissue, and urinary tract infections. None of the patients studied had meningitis.
In our model of single dosing, we showed that once the concentration of trovafloxacin fell below the MBC, bacterial regrowth occurred, suggesting that trovafloxacin has a minimal post sub-MBC effect in CSF. Because similar results have been reported in this meningitis model, 6 we believe it is prudent to space the dosing of trovafloxacin in meningitis to ensure that CSF concentrations do not fall below the MBC.
Using multiple trovafloxacin doses we compared regimens in which the doses were given every serum half-life or every two serum half-lives. Dosing intervals larger than two half-lives would allow drug concentrations to fall below the MBC. Both dosing regimens in our experiments resulted in equivalent bacterial killing at 24 and 48 h, suggesting that a dosing interval of every second half-life is sufficient. A recent study in children demonstrated trovafloxacin half-life values of 14.4 h in serum and 10.7 h in CSF. 16 If data from the rabbit meningitis model are extrapolated to humans, a once-daily dosing regimen (every second half-life) should be effective for treatment of pneumococcal meningitis. Because of possible mild dosage-related adverse reactions with this schedule (A. Arguedas-Mohs, personal communication), 16 we have chosen a 12 hourly schedule for treatment of meningitis. A multi-centre international collaborative study is currently evaluating trovafloxacin treatment for bacterial meningitis in children using a regimen similar to that used in our model with a loading dose of 5 mg/kg (equivalent to 20 mg/kg in these experiments) followed by 2.5 mg/kg every 12 h (every serum half-life).
![]() |
Acknowledgments |
---|
![]() |
Notes |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
2 . Paris, M. M., Hickey, S. M., Uscher, M. I., Shelton, S., Olsen, K. D. & McCracken, G. H., Jr. (1994). Effect of dexamethasone on therapy of experimental penicillin- and cephalosporin-resistant pneumococcal meningitis. Antimicrobial Agents and Chemotherapy 38, 13204.[Abstract]
3 . Ooie, T., Suzuki, H., Terasaki, T. & Sugiyama, Y. (1996). Comparative distribution of quinolone antibiotics in cerebrospinal fluid and brain in rats and dogs. Journal of Pharmacology and Experimental Therapeutics 278, 5906.[Abstract]
4 . Scheld, W. M. (1989). Quinolone therapy for infections of the central nervous system. Reviews of Infectious Diseases 11 , Suppl. 5, S1194202.[ISI][Medline]
5 . Craig, W. A. (1998). Pharmacokinetic/pharmacodynamic parameters: rationale for antibacterial dosing of mice and men. Clinical Infectious Diseases 26, 112.[ISI][Medline]
6 . Kim, Y. S., Liu, Q., Chow, L. L. & Täuber, M. G. (1997). Trovafloxacin in treatment of rabbits with experimental meningitis caused by high-level penicillin-resistant Streptococcus pneumoniae. Antimicrobial Agents and Chemotherapy 41,1186 9.[Abstract]
7 . Friedland, I. R., Shelton S., Paris, M., Rinderknecht, S., Ehrett, S., Krischer, K. et al. (1993). Dilemmas in diagnosis and management of cephalosporin-resistant Streptococcus pneumoniae meningitis. Pediatric Infectious Disease Journal 12, 196200.[ISI][Medline]
8 . National Committee for Clinical Laboratory Standards. (1993). Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically: Approved Standard M7-A3. NCCLS, Villanova, PA.
9 . Dacey, R. G. & Sande, M. A. (1974). Effect of probenecid on cerebrospinal fluid concentration of penicillin and cephalosporin derivatives. Antimicrobial Agents and Chemotherapy 6, 43741.[ISI][Medline]
10 . Paris, M. M., Hickey, S. M., Trujillo, M., Shelton, S. & McCracken, G. H., Jr. (1995). Evaluation of CP-99,219, a new fluoroquinolone, for treatment of experimental penicillin- and cephalosporin-resistant pneumococcal meningitis. Antimicrobial Agents and Chemotherapy 39, 12436.[Abstract]
11 . Simon, H. J. & Yin, E. J. (1970). Microbioassay of antimicrobial agents. Applied Microbiology 19, 5739.[ISI][Medline]
12 . Ebert, S. C. & Craig, W. A. (1990). Pharmacodynamic properties of antibiotics: application to drug monitoring and dosage regimen design. Infection Control and Hospital Epidemiology 11, 31926.[ISI][Medline]
13 . Vogelman, B. & Craig, W. A. (1986). Kinetics of antimicrobial activity. Journal of Pediatrics 108, 83540.[ISI][Medline]
14 . Drusano, G. L., Johnson, D. E., Rosen, M. & Standiford, H. C. (1993). Pharmacodynamics of a fluoroquinolone antimicrobial agent in a neutropenic rat model of Pseudomonas sepsis. Antimicrobial Agents and Chemotherapy 37, 48390.[Abstract]
15 . Forrest, A., Nix, D. E., Ballow, C. H., Goss, T. F., Birmingham, M. C. & Schentag, J. J. (1993). Pharmacodynamics of intravenous ciprofloxacin in seriously ill patients. Antimicrobial Agents and Chemotherapy 37,1073 81.[Abstract]
16 . Arguedas-Mohs, A., Vargas, S. L., Bradley, J. S., Loaiza, C., Rivera, R., Vincent, J. et al. (1997). Trovafloxacin CSF penetration and pharmacokinetics in children. In Abstracts of the Thirty-Seventh Interscience Conference on Antimicrobial Agents and Chemotherapy, Toronto, Canada, 1997. Abstract A-105, p. 21. American Society for Microbiology, Washington, DC.
Received 28 July 1998; returned 9 November 1998; revised 10 December 1998; accepted 6 January 1999