Oct 5, 1982 - Antimicrob. Agents Chemother. 17:993-1000. 2. n,. S. H., M. L. Corrado, P. M. Shah, M.Armen- pgd, M. Bans, and C. E. Cheubln. 1981. Past and.
ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Apr. 1983, p. 634-636 00664804/83/040634-03$02.00/O Copyright 0 1983, American Society for Microbiology
Vol. 23, No. 4
Intrathecal Penetration of N-Formimidoyl Thienamycin in Normal Rabbits: Potentiation by Coadministration of Renal Dipeptidase Enzyme Inhibitor ANTHONY W. CHOW,lt* KELVIN R. FINLAY,2 H. GRANT STIVER,1 AND CATHERINE L. CARLSON1 Division of Infectious Disease, Department of Medicine,' and Department of Ophthalmology,2 University of British Columbia and Vancouver General Hospital, Vancouver, British Columbia, Canada VSZ IM9 Received 5 October 1982/Accepted 18 January 1983
The intrathecal penetration of N-formimidoyl thienamycin (MK0787) with or without coadministration of the renal dipeptidase enzyme inhibitor (MK791) in normal rabbits was studied immediately before and after the third dose of 40 mg/kg infused intravenously at daily 6-h intervals. Mean ± standard error peak concentrations in cerebrospinal fluid were 0.23 ± 0.02 and 0.53 ± 0.12 ,ug/ml without and with coadministration of MK791, respectively (P < 0.05, Student's t test). Penetration into cerebrospinal fluid (based on the ratio of cerebrospinal fluid to plasma area under the concentration-time curves) were 4.4 and 6.0%, respectively. N-Formimidoyl thienamycin penetrated uninflamed meninges, and peak concentrations were significantly augmented by coadministration of MK791.
N-Formimidoyl thienamycin (MK0787) has potent activity against both gram-positive and gram-negative bacteria and might be useful for treatment of bacterial meningitis (5). N-Formi-
midoyl thienamycin is unique among 1-lactam antibiotics in that it is metabolized and inactivated in the brush border of the renal tubules by the dipeptidase enzyme, dehydropeptidase I, which hydrolyzes the P-lactam ring (4). The degradation of N-formimidoyl thienamycin in vivo can be halted and its concentration in urine and plasma augmented by the coadministration of a renal dipeptidase inhibitor (MK-791) in chimpanzees and humans (4). Accordingly, we studied the intrathecal penetration of N-formimidoyl thienamycin in rabbits with or without coadministration of MK791. Groups of New Zealand White female rabbits weighing 2 to 3 kg each were studied. Each rabbit was adapted in individual cages for 48 h before experimentation. Anesthesia was attained by intramuscular ketamine hydrochloride (100 mg/ml) admixed with acepromazine maleate (2.5 mg/ml). N-Formimidoyl thienamycin at a dose of 40 mg/kg alone or in combination with MK791 at a dose of 40 mg/kg was administered at 6-h intervals by intravenous bolus infusion through anterior marginal ear veins. N-Formimidoyl thienamycin (Merck Sharp & Dohme Ret Address reprint requests to Anthony W. Chow, Division of Infectious Disease, G. F. Strong Research Laboratories, Vancouver General Hospital, 700 West 10th Avenue, British Columbia, Canada VSZ 1M9.
search Laboratories, Rahway, N.J.) was prepared in sterile normal saline. Antibiotic solutions containing MK791 (Merck Sharp & Dohme Research Laboratories) were prepared by admixing stock solutions of N-formimidoyl thienamycin and MK791 in a water bath maintained at 80°C. Approximately 2.5 ml of plasma and 0.5 to 1 ml of cerebrospinal fluid (CSF) were obtained at each sampling from the anterior ear veins and cistemal space, respectively, immediately before and at 0.5, 1, 2, 4, and 6 h after the third dose of antibiotic. No bloody samples were accepted for analysis. All samples were immediately stabilized in MES (50%o [vol/vol] ethylene glycol-1 M morpholineethanesulfonate) buffer (pH 6.0) in equal proportions (vol/vol), quickfrozen in dry ice and acetone, and stored at -80°C until ready for assay. An agar diffusion bioassay technique was used with Bacillus subtilis ATCC 12432 as the test organism (1). Preliminary studies in our laboratory indicated that this bioassay technique is reproducible, with a standard error of 5% for plasma samples and 5 to 10%o for CSF, and detects a measurable concentration of 0.02 ,ug/ml (K. R. Finley, C. L. Carlson, and A. W. Chow, Invest. Ophthalmol. Visual Sci., in press). Studies with standards of plasma, CSF, or MES buffer, spiked with known concentrations of N-formimidoyl thienamycin either alone or with MK791, yielded identical results, indicating that CSF, plasma, and MK791 did not interfere with the bioassay of N-formimidoyl thienamycin. Therefore, standards for both plasma and CSF were prepared in MES buffer. 634
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TABLE 1. Concentrations of N-formimidoyl thienamycin in rabbits after daily 6-h dosages at 40 mg/kg with or without coadministration of MK791 Treatment and concn
With MK791 CSF Plasma
No. of samples
Pretreatment
4 5
0 0
Mean ± SE concn (,ug/ml) at following time (h): 0.5
1
2
4
6
0.43 ± 0.15 20.40 ± 1.90*
0.53 ± 0.12*a 3.66 ± 0.43*
0.17 ± 0.01* 0.76 ± 0.24
0 0.06 ± 0.05
0 0
Without MK791 CSF 3_5b 0 0.23 ± 0.02 0.19 ± 0.05 0.11 ± 0.01 0 0 5 Plasma 0 15.12 ± 1.31 1.98 ± 0.14 0.28 ± 0.04 0 0 a *, Significantly higher than corresponding levels achieved without MK791 (P < 0.05, Student's t test). b Three samples each for pretreatment and 4- and 6-h specimens, four samples for 2-h specimens, and five samples each for 0.5- and 1-h specimens.
The antibiotic concentrations measured in CSF and plasma were fitted to a regression line by the method of least mean squares. The elimination half-life of N-formimidoyl thienamycin in plasma and CSF was calculated by dividing ln 2 by the elimination constant K, where K = 2.3 x the slope of the line. The area under the concentration-time curve (AUC) for plasma and CSF was obtained by successive trapezoidal approximation for time = 0 to time = 00 (7). Concentrations of N-formimidoyl thienamycin in plasma and CSF attained with and without coadministration of MK791 are shown in Table 1. Mean peak plasma concentrations of 15.12 and 20.40 ,ug/ml without and with coadministration of MK791, respectively, were observed at 30 min after infusion of the third dose. Without MK791, the plasma half-life was 0.27 h, and the AUC value was 9.45 ,ug - h/ml. With coadministration of MK791, the plasma half-life was 0.45 h, and the AUC value was 14.2 pig - h/ml. The mean concentrations in plasma of N-formimidoyl thienamycin administered with MK791 were significantly higher than corresponding concentrations without MK791 at 0.5 and 1 h after infusion (P < 0.05, Student's t test) (Table 1). Mean peak concentrations of N-formimidoyl thienamycin in CSF were 0.23 and 0.53 ,ug/ml without and with coadministration of MK791, respectively (P < 0.05). Mean concentrations of N-formimidoyl thienamycin in CSF with coadministration MK791 were significantly higher than corresponding concentrations without MK791 at 1 and 2 h after infusion (P < 0.05) and were undetectable at 4 h. The CSF half-life was 1.4 and 1.0 h without and with coadministration of MK791, respectively. On the basis of the ratio of CSF AUC to serum AUC (x100), the penetration of N-formimidoyl thienamycin in CSF was 4.4% when administered alone and 6.0%o when coadministered with MK791. The penetration of N-formimidoyl thienamy-
cin in CSF of normal rabbits was relatively poor, P-lactam antibiotics (2, 5, 6). Nevertheless, the mean peak concentrations attained (0.2 to 0.5 ,ug/ml) exceeded or approached the 90%o minimal inhibitory concentrations for most susceptible bacteria potentially important in meningitis, including Neisseria meningitidis (0.02 ,ug/ml), Streptococcus pneumoniae (0.01 ,ug/ml), Haemophilus influenzae (0.1 ,ug/ml), Streptococcus agalactiae (0.1 ,ug/ml), Staphylococcus aureus (0.1 ,ug/ml), Staphylococcus epidermidis (0.2 ,ug/ml), Listeria monocytogenes (0.025 ,ug/ml), Escherichia coli (0.1 ug/ml), and Klebsiella pneumoniae (0.4 ,g/ml) (2, 3, 5, 6). In the presence of meningeal inflammation, attainable concentrations in CSF may be considerably higher (5). Importantly, coadministration of the renal enzyme inhibitor MK791, which is known to have no antibiotic effect by itself, significantly increased N-formimidoyl thienamycin concentrations in both CSF and plasma. The observations that N-formimidoyl thienamycin penetrates uninflamed meningitis at levels above the 90o minimal inhibitory concentrations for most susceptible bacteria and that its intrathecal concentrations may be further augmented by the coadministration of MK791 strongly suggest its clinical potential for empirical treatment of purulent meningitis, especially when gram-negative bacillary meningitis is suspected. Its efficacy in experimental E. coli meningitis in rabbits treated without MK791 has recently been demonstrated by Patamasucon and McCracken (5). Further investigations of its clinical efficacy in experimental meningitis should be initiated with other, more resistant gram-negative bacilli and with the coadministration of the renal enzyme inhibitor MK791. The effect of probenecid on the pharmacokinetics of both N-formimidoyl thienamycin and MK791 also deserves further study. as it is with other
We thank Karen H. Bartlett for technical assistance and Kathy Holding for preparation of this manuscript.
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ANTIMICROB. AGENTS CHEMOTHER. LITERATURE CITED
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urinary recovery of N-formimidoyl thienamycin (MK 0787) on administering an inhibitor of the renal dipeptidase responsible for antibiotic metabolism, p. 743-745. In P. Periti and G. G. Grassi (ed.), Current chemotherapy and immunotherapy, proceedings of the 12th International Congress of Chemotherapy, vol. 1. American Society for Microbiology, Washington, D.C. a 5. , P., and G. H. McCracken, Jr. 1982. Pharmacokinctics and bacteriological efficacy of N-formimidoyl thienamycin in experimental Escherichia coli meningitis. Antimicrob. Agents Chemother. 21:390-392. 6. Rahal, J. J., and M. S. Simberkof. 1982. Host defense and antimicrobial therapy in adult gram-negative bacillary meningitis. Ann. Intern. Med. 96:468-474. 7. Rowlad, M., and T. N. Tow. 1980. Clinical pharmacokinetics: concepts and applications, p. 288-291. Lea & Febiger, Philadelphia, Pa.
