Penetration of telithromycin (HMR 3647), a new ketolide antimicrobial, into inflammatory blister fluid following oral administration

F. Namour*, E. Sultan, M. H. Pascual and B. Lenfant

Aventis Pharma, Hoechst Marion Roussel/Romainville, 102 Route de Noisy, 93235 Romainville, France

Received 12 December 2001; returned 26 February 2002; revised 4 March 2002; accepted 13 March 2002.


    Abstract
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
The penetration of telithromycin (HMR 3647), a novel ketolide antimicrobial, has been assessed in an open, single-dose study in eight healthy male subjects. Following a single, oral, 600 mg dose the mean ratio of the concentration of telithromycin in blister fluid over plasma was 1.38. Significant blister fluid concentrations were maintained up to 24 h post-dose. These results indicate that telithromycin penetrates well into inflammatory extracellular fluid, achieving high and sustained concentrations in this medium.

Keywords: ketolide, telithromycin, HMR 3647, tissue penetration, inflammatory fluid, antimicrobial


    Introduction
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Telithromycin (HMR 3647) is the first member of a new family of antimicrobials—the ketolides—under development for the treatment of respiratory tract infections (RTIs). Telithromycin is active against a range of common and atypical/intracellular respiratory pathogens in vitro, regardless of macrolide or ß-lactam resistance,1,2 and has a low potential to select for, or induce, resistance in common respiratory tract pathogens.3,4

The tissue distribution of antimicrobials at sites of infection has been found to be predictive of clinical outcome.5 Tissue penetration studies have, therefore, become important aspects of the assessment of new antimicrobials. As the majority of pathogens implicated in the aetiology of RTIs are located extracellularly, the localization of antimicrobial agents in extracellular inflammatory fluids is likely to be closely related to their clinical efficacy.

The present study was conducted to determine the penetration of telithromycin into inflammatory extracellular fluid using the cantharidin ‘skin-blister’ model in healthy male subjects.


    Materials and methods
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
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Study design and procedures

This open, single-dose study included eight healthy male subjects aged 18–60 years and was conducted in accordance with good clinical practice guidelines. This study was approved by the Walton Manor Ethics Committe, Milton Keynes, UK, and written informed consent was obtained. Subjects were judged to be healthy on the basis of medical history, physical examination, routine laboratory tests, vital signs and 12-lead electrocardiograms (ECGs). Subjects were excluded if they had received treatment during the preceding 3 months with any drugs known to have potential organ toxicity, if they had symptoms of clinically significant illness during the preceding 3 months (including sick sinus syndrome or liver, gastrointestinal or kidney disease) or if they had a history of atopy or hypersensitivity to drugs with a similar structure to telithromycin. Subjects reported to the clinical research facility on the day before drug administration.

Blisters were induced with cantharidin-loaded corn plasters (0.2% mixture in paraffin wax), providing a skin contact area of 1 cm2 and were held in place on the abdomen with tape. Three plasters were applied the day before dosing (16:00 h), and a further plaster was applied on the morning of dosing (08:00 h) for collection of fluid at the 24 h timepoint. Subjects then received a single, oral, 600 mg dose of telithromycin (time 0) under fasting conditions. Subjects received orange juice or water 2 h post-dose and standardized meals as follows: lunch 4 h post-dose; snack 7 h post-dose; light snack 12 h post-dose.

Heparinized blood samples (centrifuged immediately at 4°C) and blister fluid (0.05–0.1 mL) were collected just before and at timed intervals up to 24 h after dosing. Blister fluid was withdrawn using a syringe and fine gauge needle. After sampling, the blister was sprayed with a fast-drying plastic spray to maintain blister integrity. A maximum of two samples of at least 0.05 mL could be withdrawn from each blister. Samples were stored at –20°C pending analysis. Clinical examination was carried out at screening and study end (24 h post-dose). Laboratory investigations, vital signs and ECGs were carried out at screening, pre-dosing and at study end. Adverse events were recorded throughout the study by investigator and subject observation.

Sample analysis

Plasma and blister fluid samples were analysed for telithromycin using a validated high-performance liquid chromatography (HPLC) method. Samples (with internal standard added) were deproteinated with acetonitrile. The supernatant was evaporated and reconstituted in mobile phase before injection in reverse phase chromatography (Purosphor RP18e column). The mobile phase was 0.05 M ammonium acetate/methanol/acetonitrile (52:26:22), and the column eluate was monitored by fluorimetry (excitation at 263 nm and emission at 460 nm). The lower limit of quantification was 0.005 mg/L in plasma (0.3 mL aliquot) and 0.030 mg/L (0.1 mL aliquot) or 0.150 mg/L (0.05 mL aliquot) in blister fluid. During assay the mean accuracy (relative error) of the quality control samples was between –4.7 and 6.0%, and the precision (coefficient of variation) was <7.7% over the range 0.015–0.75 mg/L.

Pharmacokinetic and statistical analysis

A non-compartmental analysis was used to calculate the following pharmacokinetic parameters for both plasma and blister fluid: maximal concentration (Cmax), time to maximal concentration (tmax), concentration 24 h after dosing (C24) and the area under the concentration–time curve [AUC0–24]. AUC0–24 was calculated using the linear trapezoidal rule between 0 and 24 h. The blister fluid to plasma AUC ratio (R) was calculated as follows: R = AUC0–24 blister fluid/AUC0–24 plasma.

Descriptive statistics (means ± S.D. for all the parameters and, in addition, the median and range for tmax, and the geometric mean for the AUC ratio) are reported.


    Results
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 Results
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Eight male subjects took part in the study: mean age 44.5 ± 7.2 years (range 36–58); mean weight 75.6 ± 5.4 kg (range 67.0–81.8). All completed the study and were included in the pharmacokinetic and safety analyses. The pharmacokinetic data are summarized in Table 1, whereas Figure 1 shows the plasma and blister fluid concentration–time profile.


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Table 1.  Pharmacokinetic parameters of telithromycin (HMR 3647) in plasma and blister fluid (means ± S.D.) following a single oral dose of 600 mg in eight healthy male subjects
 


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Figure 1. Mean telithromycin (HMR 3647) concentrations (± S.E.m.) in plasma and blister fluid following a single, oral administration of 600 mg to eight healthy male subjects. Cross, plasma; circle, blister fluid.

 
The concentration in the blister fluid was quantifiable at the first timepoint, 2 h after dosing, in seven of the eight subjects. The mean concentrations plateaued from 6 to 16 h with values ranging from 0.293 to 0.373 mg/L. Telithromycin was still quantifiable in the blister fluid of the subjects 24 h after dosing, at which time the mean concentration in blister fluid (0.080 mg/L) remained seven times higher than that in plasma (0.0120 mg/L). The mean ratio of blister fluid over plasma concentrations increased from 1.4 (6 h after dosing) to 9.9 (16 h after dosing).

The mean Cmax in blister fluid (0.44 mg/L) was reached later than in plasma (9 versus 3 h) and the geometric mean (R) of the AUC0–24 of blister fluid over that of plasma was 1.38 (Table 1).

Three adverse events were reported during the study by two subjects (headache, sore throat and dizziness). None was considered to be related to the study drug by the investigator, and all were mild or moderate in intensity. No serious adverse events were reported, and there were no clinically significant changes in any laboratory parameters, vital signs or ECG recordings.


    Discussion
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
The pharmacokinetics in plasma and blister fluid of telithromycin were determined following a single, oral dose of 600 mg using a cantharidin-induced skin blister method.

The mean ratio (R) of AUC0–24 in blister fluid to the AUC0–24 of plasma indicates that telithromycin distributed well into blister fluid, with concentrations on average 38% higher than in plasma.

Telithromycin has previously been shown to concentrate inside white blood cells (WBCs).6 Whereas such sequestration may be important against intracellular pathogens such as Chlamydia spp., interstitial fluid levels appear to be more relevant when considering the efficacy of an antimicrobial in RTIs involving Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis.5

In a previous single-dose study, concentrations of telithromycin in peripheral WBCs were shown to be much higher than in plasma,6 raising the possibility of a bias due to the presence of WBCs in the blister fluid. The volumes of blister fluid obtained in the present study did not permit the assay of telithromycin in WBCs. However, taking into account the maximum concentration of telithromycin, the mean WBC count 6 h post-dose in the previous study and the number of WBCs present in the inflammatory blister fluid, the quantity of telithromycin from WBCs present in the blister fluid of the present study would represent c. 10% of the lowest, and <2% of the highest, blister fluid concentration observed 24 h post-dose. Thus, the potential bias due to the presence of WBCs in the blister fluid appears to be minimal.

Lenfant et al.7 reported a Cmax of c. 2 mg/L following single and repeated (10 days) dosing with 800 mg telithromycin, with plasma levels well in excess of the MICs reported for the major respiratory tract pathogens such as S. pneumoniae (MIC90 0.03 mg/L),1,8 including those exhibiting ß-lactam and/or macrolide resistance.1,8 In the present study, subjects receiving a single 600 mg dose of telithromycin had Cmax (0.83 mg/L) levels somewhat lower than expected from those reported following an 800 mg dose. Despite this, the concentrations achieved in blister fluid still exceed the MICs reported for major respiratory tract pathogens. This finding supports the expectation that an 800 mg daily dose, currently under clinical development, will provide inflammatory extracellular fluid levels well in excess of those required to maintain good activity against the major respiratory tract pathogens.8

The pharmacokinetic profile of telithromycin in blister fluid is similar to that of azithromycin.9 However, the mean peak blister fluid concentration reported here is three- to four-fold higher than for azithromycin (0.44 versus 0.13 mg/L). Furthermore, the blister fluid/plasma AUC ratio (1.38 versus 0.8) is also higher for telithromycin.

The results of the present study indicate that telithromycin penetrates well into inflammatory extracellular fluid, achieving high, sustained concentrations in this medium. This, combined with its potent activity against the major community-acquired respiratory pathogens—even multidrug-resistant strains—and penetration into WBCs, suggests that telithromycin offers potential in the treatment of community-acquired RTIs.


    Footnotes
 
* Corresponding author. Tel: +33-1-4991-5807; Fax: +33-1-4991-4842; E-mail: florence.namour{at}aventis.com Back


    References
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
1 . Pankuch, G. A., Visalli, M. A., Jacobs, M. R. & Appelbaum, P. C. (1998). Susceptibilities of penicillin- and erythromycin-susceptible and -resistant pneumococci to HMR 3647 (RU 66647), a new ketolide, compared with susceptibilities to 17 other agents. Antimicrobial Agents and Chemotherapy 42, 624–30.[Abstract/Free Full Text]

2 . Felmingham, D., Robbins, M. J., Leakey, A., Cooke, R., Dencer, C., Salman, H. et al. (1997). The comparative in vitro activity of HMR 3647, a ketolide antimicrobial, against clinical bacterial isolates. In Programs and Abstracts of the Thirty-seventh Interscience Conference on Antimicrobial Agents and Chemotherapy, Toronto, Canada, 1997. Abstract F116, p. 166. American Society for Microbiology, Washington, DC.

3 . Bonnefoy, A., Agouridas, C. & Chantot, J. F. (1998). HMR 3647: antibacterial activity of resistance. In Program and Abstracts of the Fourth International Conference on the Macrolides, Azalides, Streptogramins and Ketolides, Barcelona, Spain, 1998. Abstract 1.24, p. 25.

4 . Davies, T. A., Dewasse, B. E., Jacobs, M. R. & Appelbaum, P. C. (2000). In vitro development of resistance to telithromycin (HMR 3647), four macrolides, clindamycin and pristinamycin in Streptococcus pneumoniae. Antimicrobial Agents and Chemotherapy 44, 414–7.[Abstract/Free Full Text]

5 . Bergogne-Bérézin, E. (1995). Predicting the efficacy of antimicrobial agents in respiratory infections—is tissue concentration a valid measure? Journal of Antimicrobial Chemotherapy 35, 363–71.[Abstract]

6 . Pham Gia, H., Roeder, V., Namour, F., Sultan, E. & Lenfant, B. (1999). HMR 3647 achieves high and sustained concentrations in white blood cells in man. Journal of Antimicrobial Chemotherapy 44, Suppl. A, Abstract P79, p. 57.

7 . Lenfant, B., Sultan, E., Wable, C., Pascual, M. H., Meyer, B. H. & Scholtz, H. E. (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 A49, p. 16. American Society for Microbiology, Washington, DC.

8 . Agouridas, C., Bonnefoy, A. & Chantot, J. F. (1998). In vitro activity of HMR 3647, a novel ketolide highly active against respiratory pathogens. In Programs and Abstracts of the Fourth International Conference on Macrolides, Azalides, Streptogramins and Ketolides, Barcelona, Spain, 1998. Abstract 1.12, p. 22.

9 . Cooper, M. A., Nye, K., Andrews, J. M. & Wise, R. (1990). The pharmacokinetics and inflammatory fluid penetration of orally administered azithromycin. Journal of Antimicrobial Chemotherapy 26, 533–8.[Abstract]