Antibacterial activity of telithromycin (HMR 3647) in relation to in vitro simulated human plasma kinetics

Alain Bonnefoy,* and Pascal Le Priol

Aventis–Hoechst-Marion-Roussel, Infectious Diseases Group, 102 Route de Noisy, 93235 Romainville Cedex, France


    Abstract
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 Abstract
 Introduction
 Materials and methods
 Results and discussion
 References
 
Telithromycin (HMR 3647) is a ketolide suitable for the treatment of respiratory infections. The aim of this study was to demonstrate its antibacterial efficacy against an erythromycinsusceptible Staphylococcus aureus, an erythromycin-resistant Streptococcus pneumoniae and Haemophilus influenzae. The free serum concentrations of telithromycin, produced by repeated oral administration of 800 mg to adults for 10 days, was simulated in an in vitro system. The ketolide displayed bacteriostatic activity against all three strains tested. This study supported the observation that an 800 mg po dose of telithromycin demonstrated antibacterial efficacy against respiratory tract pathogens.


    Introduction
 Top
 Abstract
 Introduction
 Materials and methods
 Results and discussion
 References
 
Telithromycin (HMR 3647) is the first antibiotic belonging to a new class of 14-membered ring macrolides named ketolides. Telithromycin exhibits marked in vitro activity against a large bacterial spectrum, including multidrug-resistant pneumococci, staphylococci, streptococci, Haemophilus influenzae, Moraxella catarrhalis and intracellular respiratory pathogens such as Chlamydia pneumoniae.1 Telithromycin is expected to be administered od, based on its increased pharmacodynamic efficiency and a favourable kinetic profile.2

Kinetic models for evaluation of antibiotic activity permit the production of in vitro drug levels of similar pharmacokinetics to those found in vivo during therapy.3 The aim of this study was to explore the antibacterial efficacy of telithromycin modelled in an in vitro system simulating the free serum concentrations produced by repeated administration of a po dose of 800 mg od to adults for 10 days.


    Materials and methods
 Top
 Abstract
 Introduction
 Materials and methods
 Results and discussion
 References
 
Antimicrobial agent and bacterial strains

Telithromycin was prepared at Hoechst-Marion-Roussel (Romainville, France).

The clinical isolates tested were an erythromycinsusceptible Staphylococcus aureus (011UC4), an erythromycin-resistant Streptococcus pneumoniae (030MV2) and a ß-lactamase-producing H. influenzae (350RD7). The MICs of telithromycin for these organisms, as measured by a two-fold agar dilution method,4 were 0.04, 0.15 and 0.6 mg/L, respectively.

In vitro kinetic model

The in vitro model, designed to prevent dilution of the bacterial inoculum, has been described previously.5 The system consists of a reservoir containing brain–heart infusion (BHI, Diagnostic Pasteur, Marnes la Coquette, France), a second reservoir containing the antibiotic in BHI and a 2 L laboratory bioreactor (Applikon, Les Mureaux, France) that represents the peripheral compartment containing the bacteria in the test medium. BHI was supplemented with 4% red cell extract (Diagnostic Pasteur), allowing the growth of S. pneumoniae and H. influenzae. Preliminary studies showed that the best growth in the bioreactor was obtained by preparing initial inocula as follows. The inoculum was an overnight culture [optical density at 600 nm (OD600) of c. 1], an exponential phase growth culture (OD600 0.3) or a bacterial suspension (OD600 1) in the case of S. aureus, S. pneumoniae and H. influenzae, respectively. The antibiotic was added after 1 h incubation. Samples (1 mL) were removed from the fermenter over a 6 h period at regular intervals for determination of both viable counts and antibiotic concentrations. Viability was determined by spiral plating on to Mueller–Hinton agar plates (Diagnostic Pasteur), supplemented according to the strain tested,4 with incubation overnight at 37°C, in a 5% CO2 enriched atmosphere in the case of S. pneumoniae and H. influenzae. Carry-over of antibiotic was avoided by using adequate dilutions of samples. The lower limit of detection was 400 cfu/mL. Antibiotic concentrations were measured by microbiological assay with Bacillus subtilis ATCC 6633 spore suspensions as indicator strain in agar test Medium A (Merck, Nogent sur Marne, France).6 Each experiment was performed in duplicate.

The human pharmacokinetic profile has been simulated in accordance with data obtained in 12 volunteers having received telithromycin 800 mg po od for 10 days.2 Protein binding was estimated to be close to 70%.7 Only free concentrations were taken into account.


    Results and discussion
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 Abstract
 Introduction
 Materials and methods
 Results and discussion
 References
 
Pharmacokinetic analysis

The validity of our in vitro infection model was established by measuring telithromycin concentrations at various times. After 10 days administration of 800 mg telithromycin po in healthy volunteers, previously reported maximal plasma concentration and the area under the concentration–time curve (AUC), expressed as total concentrations, were 1.84 ± 1.14 mg/L and 8.49 ± 2.59 mg•h/L, respectively.2 Protein binding being 70%,7 the free targeted peak and AUC were calculated as 0.55 ± 0.34 mg/L and 2.55 ± 0.78 mg•h/L, respectively. The TableGo shows that the experimental data were similar to the pharmacokinetic parameters observed, with a peak of 0.7 mg/L and AUC of 3 mg•h/L.


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Table. Pharmacokinetic analysis of telithromycin (free concentrations, represented as mean ± S.D.)
 
Antibacterial activity

The FigureGo summarizes the resultant killing curves. Against susceptible S. aureus, telithromycin led to a decrease in log10 cfu/mL from 7.4 to 6.3 after 6 h, while the untreated inoculum reached 8.7. In the case of erythromycin-resistant S. pneumoniae, only a 0.5 log10 decrease was observed. Against H. influenzae, telithromycin was clearly bacteriostatic, maintaining the inoculum at a level of 8.7 log10 cfu/mL. In the same time, the untreated control increased from 8.3 to 9 log10 cfu/mL.



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Figure. In vitro antibacterial activity of telithromycin against S. aureus 011UC4 (a), S. pneumoniae 030MV2 (b) and H. influenzae 350RD7 (c). ({diamondsuit}) control, ({blacksquare}) telithromycin. Telithromycin was applied at concentrations simulating an 800 mg po od dose for 10 days in humans after 1 h incubation of bacteria.

 
These results are in accordance with those usually obtained by classical time–kill assays at a constant MIC multiple concentration.8,9 Our data support the choice of 800 mg telithromycin po as an od dose, since this regimen retains plasma concentrations consistently higher than, or at least equal to, MICs, whatever the bacterium tested. These results are in agreement with those obtained in a murine thigh-infection model, in which it was reported that the AUC/MIC was the major determinant of in vivo activity for telithromycin, and that od dosing would be appropriate for this ketolide.10 However, in vivo conditions at the site of infection often being more unreliable than those in a controlled in vitro model, this dosing deserves confirmation in a clinical setting.


    Notes
 
* Corresponding author. Tel: +33-1-4991-4778; Fax: +33-1-4991-5061; E-mail: Alain.Bonnefoy{at}Aventis.com Back


    References
 Top
 Abstract
 Introduction
 Materials and methods
 Results and discussion
 References
 
1 . Boswell, F. J., Andrews, J. M., Ashby, J. P., Fogarty, C., Brenwald, N. P. & Wise, R. (1998). The in-vitro activity of HMR 3647, a new ketolide antimicrobial agent. Journal of Antimicrobial Chemotherapy 42, 703–9.[Abstract]

2 . Lenfant, B., Sultan, E., Wable, C., Pascual, M. H. & Meyer, B. H. (1998). Pharmacokinetics of 800 mg once daily oral dosing of the ketolide HMR 3647 in healthy young volunteers. In Program and Abstracts of the Thirty-eighth Interscience Conference on Antimicrobial Agents and Chemotherapy, San Diego, CA, 1998. Abstract A-49, p.16. American Society for Microbiology, Washington, DC.

3 . Grasso, S. (1985). Historical review of in-vitro models. Journal of Antimicrobial Chemotherapy 15, Suppl. A, 91–102.[Abstract]

4 . Agouridas, C., Bonnefoy, A. & Chantot, J. F. (1997). Antibacterial activity of RU 64004 (HMR 3004), a novel ketolide derivative active against respiratory pathogens. Antimicrobial Agents and Chemotherapy 41, 2149–58.[Abstract]

5 . Isert, D., Klesel, N., Markus, A., Seibert, G. & Schrinner, E. (1989). Synergistic antibacterial activity of cefotaxime and the penem HRE 664 in an improved in vitro model simulating serum and tissue pharmacokinetics. Journal of Chemotherapy 4, Suppl., 479–81.

6 . Courvalin, P., Goldstein, F., Philippon, A. & Sirot, J. (1985). Fiches techniques d'étude pratique des antibiotiques. In L'antibiogramme, 1st edn, (Courvalin, P., Goldstein, F., Philippon, A. & Sirot, J., Eds), pp. 237–44. Mpc-Videom, Paris.

7 . Bree, F., Combes, O. & Tillement, J. P. (1997). Study of the binding of HMR 3647 in vitro to human serum proteins and erythrocytes. Internal Report Hoechst-Marion-Roussel 96/8683/CN.

8 . Pankuch, G. A., Hoellman, D. B., Lin, G., Bajaksouzian, S., Jacobs, M. R. & Appelbaum, P. C. (1998). Activity of HMR 3647 compared to those of five agents against Haemophilus influenzae and Moraxella catarrhalis by MIC determination and time–kill assay. Antimicrobial Agents and Chemotherapy 42, 3032–4.[Abstract/Free Full Text]

9 . Boswell, F. J., Andrews, J. M. & Wise, R. (1998). Pharmacodynamic properties of HMR 3647, a novel ketolide, on respiratory pathogens, enterococci and Bacteroides fragilis demonstrated by studies of time–kill kinetics and postantibiotic effect. Journal of Antimicrobial Chemotherapy 41, 149–53.[Abstract]

10 . Vesga, O., Bonnat, C. & Craig, W. A. (1997). Pharmacodynamic activity of HMR 3647, a new ketolide. In Program and Abstracts of the Thirty-seventh Interscience Conference on Antimicrobial Agents and Chemotherapy, Toronto, Ontario, Canada, 1997. Abstract F-8, p. 255. American Society for Microbiology, Washington, DC.

Received 19 September 2000; returned 1 November 2000; revised 10 November 2000; accepted 27 November 2000